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1

How do we tell if a familial disease is due to genetic?

1. For Mendelian pattern
a) Large Mendelian pedigree
2. For non Mendelian pattern:
a) Familial clustering
b) Twin studies
c) Adoption studies

2

What is familial clustering?

1. Shows that a disease runs in the family
2. Aims to show that the closer the genetic relationship, the higher the risk of disease
*it should be kept in mind that families also share their environment as well as genes

3

How much DNA do you share with your cousins and siblings?

1. Siblings: 50%
2. Cousins: 25%

4

How are twin studies beneficial in identifying genetic condition?

1. Based on deferences in the disease incidence between monozygotic and dizygotic twins
2. MZ twins share 100% of their genes and DZ 50%
3. Genetically determined diseases show a higher concordance in MZ twins than DZ

5

What are the two designs for adoption studies?

1. Identify individual with a disease > ascertain whether the disease runs in the biological or adopted family
2. Identify disease in individuals whose children have been adopted > ascertain whether adoption saves children from being affected

6

What is genetic disease?

Any disease which results in change of genetic material

7

How can genetic material be affected?

1. Single gene: single gene disease
2. Multiple genes: polygenic disease
3. Chromosome: chromosomal disease
4. Multiple genes and environment: multifactorial disease

8

What are the two types of cell affected in genetic disease?

1. Germline cells: sperm and ova (inherited conditions)
2. Somatic cells: non germ cells (non inherited conditions)

9

What is an example of a single gene genetic disease?

Phenyketonuria
1. Autosomal recessive
2. Incidence 1:10 000
3. Lack of phenylalanine hydroxylase (enzyme which converts phenylalanine to L tyrosine)
5. When there is access phenylalanine, your body uses alternative pathway to get rid of them which produces phenyl ketones
6. These products then gets deposited in the brain which causes mental retardation
4. Among the other effects are:
a) Microcephaly
b) Growth failure

10

What are features of a single gene condition?

1. Pathological mutation: people who have this variant has a high risk of getting this disease
2. The disease is only present in people who have this variant (affected carriers)
3. Significantly alter the gene and protein
4. Eg: Huntington's disease

11

What are features of a complex disease?

1. Normal variants
2. Present in everyone: although we have this disease or not we have this variant
3. Subtly alters gene and proteins (the occurrence of disease depend on the environment)

12

What are common features of Mendelian genes and chromosome?

1. Come in pairs
2. One of each pair is picked at random and is passed on to each child

13

What occurs during the first meiotic division?

Independent segregation of the paternal and maternal homologous chromosome

14

What occurs during the second meiotic division?

Separation of sister chromatids

15

What are the two types of chromosomal abnormalities?

1. Numerical abnormality
2. Structural abnormality

16

Describe the normal chromosomal constitution

1. Normal germ cell: haploid chromosomal constitution (23 or often referred to as N)
2. Normal somatic cell: diploid chromosomal constitution (2N)

17

Describe abnormal chromosomal constitution

1. Polyploidy: cells have chromosome in multiples of N greater than 2N
a) Triploidy
b) Tetraploidy
2. Aneuploidy: there is variation in number of chromosomes that is not in multiple of N

18

What are features of triploidy?

1. Commonest form of polyploidy
2. Usually results in miscarriage of foetus
3. Arises by:
a) Fertilisation of egg by two spermatozoa (dispermy)
b) Fertilisation of diploid gamete (due to failure of maturation of egg or sperm)

19

What are features of tetraploidy?

1. Arises from failure of completion of the first zygotic mitotic division
2. Incompatible with life

20

What is monosomy of a chromosome and what are its effects?

1. Monosomy: loss of copy of a chromosome
2. All complete monosomy of autosomal chromosomes are lethal
3. However partial monosomies may be observed in unbalanced translocation
4. The only complete monosomy that is not lethal is monosomy of X chromosome (Turner's syndrome)

21

What is trisomy 18 known as?

Edwards Syndrome

22

What are the two causes of aneuploidy?

1. Non disjunction: failure of chromosomes or sister chromatids to separate at anaphase in cell cycle
2. Anaphase lag: delayed movement of chromosomes after separation at anaphase

23

What is Klinefleter's syndrome?

47XXY

24

What is the way to obtain a XYY make up?

Non disjunction in meiosis 2 of spermatogenesis

25

How does mosaic Down syndrome occur?

When there is mitotic non disjunction occurs shortly after conception whereby some cells are normal but some cells are trisomic

26

How does structural abnormality of chromosome occur?

1. As a result of chromosome breakage and usually involves one or two chromosome
2. Can be spontaneous
3. Rate is increased by exposure to mutagenic agents such as ionising radiation and certain chemicals
4. Rate is also increased in certain inherited conditions with defects of DNA replication and repair (Eg: Blooms syndrome)

27

What are types of single chromosomal abnormality?

1. Deletion: loss of part of chromosome
2. Inversion: inversion of segment of chromosome
a) Pericentric; involves centromere
b) Paracentric; does not involve centromere
3. Duplication: duplication of chromosomal segment in tandem or in inverse configuration with original sequence
4. Isochrome: duplication of one arm of the chromosome coupled with loss of other arm (chromosome consists of two identical arm)

28

What are types of chromosomal abnormality involving two chromosomes?

1. Insertion: breakage of material from one chromosome and insertion into another chromosome
2. Translocation: exchange of materiel between two chromosomes
a) Reciprocal translocation: reciprocal exchange of material between two chromosomes
b) Robertsonian translocation: only involves acrocentric chromosomes

29

What are acrocentric chromosomes?

Chromosomes with very short arms (13, 14, 15, 21 and 22)

30

What are the outcomes in reciprocal translocation?

1. Normal
2. Carrier of balanced translocation
3. Partial trisomy of one of the involved chromosomes accompanied by partial monosomy of the other chromosome and vice versa

31

What are outcomes in Robertsonian translocation?

1. Normal
2. Carrier of balanced translocation
3. Complete trisomy of one of the involved chromosome
4. Complete monosomy of one of the involved chromosome

32

What is the phenotypic consequence of chromosomal abnormality?

Depends on whether it involves:
1. Single gene
a) If translocation to a region of active chromatin domain causes inappropriate expression (myc in Burkitt's lymphoma)
b) Creates chimaeric gene that expressed altered protein (ABL in chronic myeloid leukaemia)
2. Small group of genes
a) Resulting phenotype of attributed to a lack of product of several genes
b) Known as contiguous gene syndrome
3. Large region of chromosomes with many genes or whole chromosomes
a) Results in severe birth defects including mental/ growth retardation and specific abnormalities
b) Largely due to dosage imbalance of only a few genes on those chromosomes
c) For most genes, having an extra copy/lack of one copy results in 50% increase/decrease in its product which is unlikely to be significant

33

How do we tell if a disease is genetically inherited?

Congenital (conditions present at birth)
1. Can be genetic or environmental
2. Some genetic conditions may not necessarily be present at birth
3. Genetic conditions affecting somatic cells arise later on in life
Familial
1. There are inherited (genetic) disease that may not appear to be familial (recessive conditions)
2. Can be genetic or environmental (same family subjected to the same environment)
3. Genetic conditions affecting somatic cells are not familial

34

Why do blastomeres become small at each cell division?

They are inside the zone pellucida which is a thick layer that cannot expand thus inhibits their growth. Every new cell is only half as large as the cell it derives from

35

What are features of blastomeres?

1. Totipotent
2. The embryo has no polarity at this stage
3. The blastomeres (which were initially loose) now maximises their contact and cells are held together by tight junction
4. Cells on the inside communicate using gap junction and segregate form the cell on the outside
5. Arises through cleavage of zygote

36

When is a morula formed?

96 hours after fertilisation

37

What are features of a morula?

1. A collection of about 30 blastomeres
2. Cells on the outside become the outer cell mass (placenta) and cells on the inside the inner cell mass (embryo)
3. The point at which the first differentiation occurs

38

What causes differentiation of cells in an embryo?

1. All cells of the embryo contains the same DNA
2. Cells become different because they use different portion of this DNA and express different genes

39

When does the first molecular difference established and how?

1. They are first established after compaction when outer cell mass and inner cell mass are exposed to different environments
2. Outer cells
a) Express Cdx2
b) Cdx2 converts cells to trophoectoderm
3. Inner cells
a) Express Oct4
b) Mains cell pluripotent

40

How is a blastocyst formed?

1. Through compaction of cells and accumulation of intercellular fluid leading to the formation of blastocyst cavity
2. Consists of:
a) Embryoblast: 12 ES cells
b) Trophoblast: single cellular layer of 100 cells

41

When does hatching and implantation occur?

Occurs on the 5th day when blastocyts emerges from the pellucid zone

42

What occurs during implantation and why is it important?

1. Blastocyst adheres on the endometrium
2. It is essential to establish feto-maternal blood circulation

43

How is the endoderm created?

Though the action of cells that have invaginated the epiblast and displaced the hypoblast

44

What is the difference between epithelial cell and mesenchymal cells?

Epithelial cells
1. Closely connected to each other by tight junction, gap junctions and adherents junction
2. Have an apico-basal polarity
Mesenchymal cells
1. Lack polarisation
2. Have loose contact

45

What occurs to epiblast cells during epithelio-mesenchymal transition

1. Epiblast cells which are closely bound together loose their contact and become motile
2. Key change in EMY is that epithelial cells stop expressing high levels of E caderin (forms tight junction)

46

When is epithelio-mesenchymal transition necessary?

1. Essential for embryonic development
a) Gastrulation
b) Formation of neural crest
c) Formation of palate
2. It also occurs in cancer

47

When does formation of the face occur?

4th week of gestation

48

When does face formation almost completed?

7th week of gestation

49

What occurs to facial development from 8th week of gestation to birth?

Final development of the face occurs slowly due to changes in proportions of the facial components

50

What does the ectoderm form?

1. Skin
2. Oral epithelium
3. Tooth enamel
4. Cranial nerves

51

What does the mesoderm form?

1. Muscle
2. Part of skeleton

52

Who does the endoderm form?

Endocrine glands

53

What does the cranial neural crest form?

1. Craniofacial skeleton (bones and cartilage)
2. Tendons
3. Connective tissue of tooth
4. Sympathetic ganglia
5. Glial cells
6. Melanocytes

54

Where are cranial neural cells derived from?

Midbrain and hindbrain

55

What is the derivative of the first branchial arch?

1. Mandible
2. Maxilla
3. Meckel's cartilage
a) Incus and malleus of inner ear
b) Sphenomandibular ligament
c) Sphenomalleolar ligament

56

What is the derivative of the second branchial arch?

1. Reichert's cartilage
a) Styloid process
b) Stylohyoid ligament
c) Lesser horns of hyoid bone
d) Upper part of body of hyoid

57

What is the derivative of the third branchial arch?

1. Lower parts of body of hyoid
2. Greater horns of the hyoid bone

58

What is the derivative of the fourth branchial arch?

Cartilages of the larynx

59

What are the products of the remodelling of the pharyngeal arch arteries?

1. Carotid artery
2. Arch of aorta
3. Ductus arteriosus

60

Which cranial nerves innervate muscles from the 1st, 2nd and 3rd pharyngeal arches?

1. 5th cranial nerve (trigeminal)
2. 7th cranial nerve (facial)
3. 9th cranial nerve (glossopharyngeal)

61

List the 5 facial prominences

1. Frontonasal process x1
2. Maxillary process x2
3. Mandibular process x2

62

Describe the process of facial development

1. Localised thickenings (olfactory placode) develop within the ectoderm of the frontal prominence
2. Rapid plofireatiom of mesenchyme around the placode produces a horseshoe shaped ridge which forms the nasal pit
3. Lateral arm of the ridge is known as lateral nasal process and the medial arm the medial nasal process
4. The maxillary process grows medially but remains separated from
a) Medial nasal process: bucconasal groove
b) Lateral nasal process: nasolacrimal groove
5. The region of the frontal process where the nose will develop is known as the frontonasal region
6. The medial nasal process continues to grow > gets displaced mesially > fuses with anatomic counterpart > forms
a) Philtrum
b) Bridge of nose
c) Part of maxilla carrying incisor teeth and primary palate
7. Maxilla also grows mesially and fuses with the medial nasal process with forms the upper lip
8. The lower lip is formed when two streams of ectomesenchyme from the mandibular process fuse together
9. Fusion between the maxillary process and lateral nasal processes occur after the nasolacrimal groove separates to form the nasolacrimal duct

63

What are the requirements of successful facial development?

1. The facial processes need to fuse to generate intact face
2. Facial progression need to reach the right size (influenced by generation, migration and proliferation of NCC)
3. The epithelial between the processes must disappear
a) Epithelial cell death
b) Epithelio-mesenchymal transition

64

What does a palate do to the primary stomodeal?

Divides the stomodeal into oral and nasal cavity

65

When does the secondary plate formation commence and end?

1. Commence: 7-8 weeks of gestation
2. Ends: 3rd month of gestation

66

Describes the process in secondary palate formation?

1. The nasal septum grows downwards from frontonasal region
2. Two palatine shelves (one from each side) extend from maxillary process towards the midline
3. The shelves are initially directed downwards towards each side of the tongue
4. After 7 weeks, the tongue is withdrawn form the shelves thus the shelves elevate and fuse with each other above the tongue
5. In the process they also fuse with the primary palate
6. The septum and the two shelves converge and fuse along the midline thus separating the primitive oral cavity into nasal and oral cavities

67

What is necessary for the fusion of palatine shelves to occur?

Disintegration of epithelial cells covering the shelves must occur (via epithelio-mesenchymal transition)

68

What is the cause of cleft palate?

1. Delayed elevation of palatial shelves
2. Defective shelf fusion

69

What are the two types of bone in the head?

1. Endochondral bone (formed via cartilage)
2. Intramembranous bone (formed via direct ossification)

70

What is the origin of head skeleton?

1. Mostly by neural crest cells (forms all facial skeleton)
2. Also paraxial mesoderm

71

What are two parts of the skull?

1. Neurocranium: calvaria and cranial base
2. Viscerocranium: facial skeleton

72

What are the two forms genes can be recognised as?

1. DNA sequence for a protein product (deduced from the product they produce)
2. Mendelian characteristics (where their existence is deduced solely from pattern of inheritance)

73

What causes Mendelian characteristics?

Segregation of a single pair of alleles located on an autosome or the X chromosome which governs a dominant, co dominant or recessive phenotype

74

Define an allele

Alternative forms of a gene or marker which segregates at meiosis

75

Define locus

The location/site of a gene or marker on a chromosome

76

Distinguish genotype and phenotype

1. Genotype: the genetic consitution
2. Phenotype: the observable character

77

Distinguish homozygous, heterozygous and hemizygous

1. Homozygous: both alleles are the same (recessive characters are expressed in homozygotes)
2. Heterozygous: the alleles are different (dominant characters are expressed in heterozygotes)
3. Hemizygous: when there is only one allele (Eg: males are hemizygous for loci on the X chromosome)

78

Describe features of autosomal dominant inheritance

1. Most makings are between heterozygote affected individual with a homozygote unaffected individual
2. Most clinically significant dominant traits are characterised by low frequencies
3. For AD inheritance to be demonstrated, several requirements must be met:
a) Every affected individual must have at least one affected parent
b) Both males and females should be affected and equally capable of transmitting the trait (provided it doesn't cause sterility)
c) There is no skipping of generation
d) Father to son and mother to daughter transmission should be as common as father to daughter and mother to son
e) An affected person should transmit the trait to half their offspring if the mating is Aa x aa (recurrence risk is 50%)

79

What are problems of pedigree interpretation?

1. Penetrance: genotypically affected but phenotypically unaffected
2. Delayed onset: may present later on in life phenotypically
3. New mutation: not present in genotype or phenotype but is passed on to future generation
4. Variable expression: two siblings inherit the same condition but express it at different severity
5. Non paternity

80

What are features of autosomal recessive inheritance?

1. Only homozygotes are affected but heterozygotes may be detected biochemically
2. The type of pedigree pattern seen is dependant on the population frequency of the gene and ability of affected individuals to reproduce
3. Most affected individuals are a product of mating between heterozygote carriers
4. A typical pedigree consist of single sibship (group of offspring having the same parent) containing affected person
5. Most cases appear sporadic with no previous family history makes pedigree interpretation difficult
6. For very rare traits, consanguinity may be increased

81

What are features of x linked disease?

1. May be recessive (common) or dominant (rare)
2. Male to male transmission CANNOT occur
a) Affected male transmits the mutant gene to ALL daughters but NONE of the sons
b) The daughter will be affected if trait is dominant
c) The daughter will be carrier if trait is recessive
3. Manifesting heterozygote do occur
4. Unaffected males NEVER transmit the gene
5. If the carrier is females
a) Risk to her son is 50% (affected)
b) Risk to her daughter is 50% affected (if dominant) or carriers (if recessive)
6. Affected homozygous females are very rare

82

What are clinical and molecular genetics of Treacher Collins syndrome?

1. Autosomal dominant inheritance
2. Affects 1/50000 live births
3. High rate of new mutation
4. Results from mutation of TCOF1 which encodes for nuclear protein, Treacle
5. Clinical features include:
a) Down slanting eyes
b) Unusual external ears
c) Flattening of zygomatic region
d) Posterior rotated ears

83

When does fusion of the primary palate occur?

5th week of gestation

84

What structures are formed from the fusion of the primary palate?

Upper lip and hard palate that is as far back as the incisive foramen

85

What causes the tongue to grow forward thus enabling the palatial shelves to elevate?

Lifting of the upper facial process from thorax

86

What are features of submucous cleft palate?

1. Bifid uvula
2. No palatine raphe
3. Notch in posterior hard palate

87

List the prevalence of cleft lip and palate in boys and girls

Cleft lip and palate is more common in boys
Cleft palate is more common in girls

88

Which side of the body does clefts occur more commonly on?

Left side is twice more common than right

89

What are environmental risk factors for cleft lip/palate?

1. Drugs
2. Vitamins
3. Nutrition
4. Alcohol
5. Smoking

90

What are 7 main components of cleft lip/palate problem?

1. Embryological disturbances
2. Foetal distortion
3. Post surgical distortion
4. Dental anomalies
5. Impaired speech
6. Impaired hearing
7. Psychological development

91

What are the 3 types of post surgical distortion in cleft lip/palate?

1. Vertical (increased lower face height)
a) Predisposition to have lower facial height
b) Airway adaptation (anatomical and inflammatory)
c) Tongue position
2. Transverse
a) Segmental
b) Dentoalveolar
3. Antero-posterior
a) Incisor displacement
b) Premaxillary distortion
c) Maxillary ankylosis

92

Why is nasal breathing difficult for patients with cleft lip/palate?

1. Small bony nasopharynx
2. Deviated nasal septum
3. Vomerine spurs
4. Atresia of nostril
5. Turbinate hypertrophy
6. Maxillary growth deficits

93

What are the dental anomalies associated with cleft lip/palate?

1. Missing teeth (usually lateral incisor)
2. Supernumerary teeth
3. Ectopic teeth
4. Malformed teeth
5. Hypoplasia

94

How are patient with cleft lip/palate more prone to ENT problems

1. Dysfunction of Eustachian tube (can't pop their ears)
2. Causes build up of fluid
3. Leads to otitis media
4. Hearing loss (affects 90% of children with cleft lip/palate)

95

What are features of enamel?

1. 96% inorganic material
2. Produced by epithelial cells
3. Small amount of organic material
4. Mature enamel is acellular and cannot be regenerated

96

What are features of dentin?

1. Very high mineral content (70% inorganic material)
2. Organic component
3. Supports enamel
4. Avascular

97

What are features of cementum?

1. Connected to dentine
2. Highly mineralised connective tissue
3. Avascular tissue

98

What are the steps in mineralisation?

1. First crystal
a) Sufficient mineral ions in the micro environment
b) Stable crystal nuclei
c) Nucleation (start of mineral growth)
2. Oriented crystal growth
a) Matrix protein
b) Collagen
3. Crystal proliferation
a) More proteases added to crystal leading to more ions added
4. Crystal matures
a) Remodelling
b) Shape and size of collagen and matrix protein are altered

99

What are the two theories of dental hard tissue formation?

1. Mineralisation initiated by vesicles secreted by cell
2. Mineralisation is regulated by extra cellular matrix protein as minerals are deposited within and around collagen fibrils

100

What are the components in the mineralised matrix of enamel?

1. Apatite
2. Amelogenin (structural role)
3. Ameloblastin (structural role)
4. Enamelin
5. Protease

101

What are the components in the mineralised matrix of dentine?

1. Apatite
2. Collagen
3. SIBLING protein (DSPP protein is the main type)
4. Gla-proteins (inhibit mineralisation)
5. Proteoglycans

102

What are the two types of digesting protein found in enamel?

1. Enamelysin
2. Kallikrein IV

103

What are proteoglycans?

1. Extra cellular protein consisting of protein core and GAG chains (hydrophilic and attracts water)
2. Involved in adhesion as it binds to cell and also binds to ECM which gives indirect connection to cell
3. Involves in signalling via ECM

104

What occurs when there is a defect at the dentino-enamel junction?

Enamel shears away from the DEJ

105

What occurs when there is a defect at the secretory stage?

Enamel is thin or hypoplastic (hypoplasia occurs when there is disruption in crystal elongation)

106

What occurs if there is defect in the protein involved in maturation stage? (Kallikrien IV and Enemelysin)

Soft of hypo mature enamel that wears off easily

107

What are features of amelogenin?

1. 90% of ameloblast protein (the most abundant protein in enamel)
2. Hydrophobic
3. Made up of proline, glutamine and leucine
4. It is found on both X and Y chromosome thus quite heterogenous and exhibits various severity
5. Mutation of amelogenin causes amelogenenis imperfecta
6. Orientates the shape and length of enamel crystal (causes formation of rod like structures)
7. Determines enamel thickness (crystal elongation)
8. Quite small protein (175 amino acids)
9. Aggregate in little blobs known as nanosphere which comes together to build up a structure during amelogenesis

108

What are features of Enamelin?

1. Hydrophobic with both acidic and basic domains
2. Mutation of this protein also causes amelogenesis imperfecta
3. Also involved in crystal elongation but have other functions
4. Quite a big protein (186 kDa glycoprotein)
5. Found in much smaller percentage in enamel
6. Loss of Enamelin leads to rough and pitted enamel (reduces the enamel hardness to bone which causes it to crumble away easily)

109

Which form of Enamelin has a known function?

1. MMP 20 cleaves the Enamelin into smaller protein
2. The rest gets discarded except 32kDa (the only form with known function)
3. Has phosphate groups and sugar residues which have been added to the protein making it hard for MMP to bind to

110

What are the 3 distinct protein products of DSPP?

1. DSP: dentin sialoprotein (heavily glycosylated)
2. DGP: dentin glycoprotein
3. DPP: dentine phosphoprotein (highly phosphorylated repetitive protein)

111

What are features of DSPP protein?

1. Stands of dentine sialophosphoprotein
2. Makes up 10% of dentine
3. The order of its products are DSP > DGP > DPP
4. DPP binds to collagen and moves to mineralisation site
5. It is a SIBLING protein (Small Integrin Binding Ligand N-linked Glycoprotein)
6. Major protein involved in dentinogenesis
7. Prevents calcospherites (tiny circles containing calcium) from sticking together

112

Distinguish hyperplasia and hypertrophy

Hyperplasia
1. Proliferation of cells of organs/tissues
2. Cells are same size but increase in number of cells
3. Occurs in first trimester (weight and height gain)
Hypertrophy
1. Increase in size of cell but number of cells remain the same
2. Occurs in last trimester (weight gain)

113

Distinguish embryo and foetus

Embryo: 1-8 weeks
Foetus: 8 weeks onwards

114

What are the two growth hormones constantly secreted from prenatal to adulthood?

1. Insulin
2. Insulin like growth factors

115

How does the release of growth hormones vary?

1. There are 5 pulses of GH during day
2. Largest peak of GH is at night
3. Peak GH occurs during puberty and declines in old age (somatopause)
4. Stimulated by Ghrelin (which stimulates hunger) and Ghrelin causes the release of GH

116

How many hormones does the hypothalamus secrete?

9 hormones

117

What are the major hormones in the body and where are they secreted?

Pituitary gland
1. Growth hormone
2. Thyroid stimulating hormone
Pineal gland
1. Melatonin (wake-sleep cycle)
Thyroid gland
1. Thyroxine T4
2. Triiodothyronine T3
3. Calcitonin
Adrenal gland
1. Epinephrine
2. Norepinephrine
Testis
1. Androgen
Pancreas
1. Insulin
2. Glucagon
Ovary
1. Oestrogen
2. Progestin

118

What are features of growth hormone?

1. Acts via G protein coupled receptor
2. Stimulates cAMP synthesis
3. Also known as somatotrophin
4. Stimulates cell growth by
a) Increasing rate of protein synthesis (by increasing the rate of amino acid intake uptake and protein incorporation in cells)
b) Release of Insulin Like a Growth Factors (IGF) from liver cells (also known as somatomedins)
5. Produced by anterior pituitary gland
6. Peptide hormone 191 aa
7. Many actions are anabolic and mediated through IGF

119

Describe the activation of tyrosine kinase

1. May be receptors with a dimer
2. Upon binding of ligand or hormone to the receptor, it phosphorylates itself with ATP from the intracellular space (auto phosphorylation) which causes the receptor to dimerise and bind together
3. Eg of hormones:
a) IGF
b) Insulin

120

Describe the mechanism in which growth hormone is regulated

1. Hypothalamus produces
a) Growth hormone releasing hormone OR
b) Growth hormone inhibiting hormone (somatostatin)
2. In the presence of GHRH, the anterior pituitary gland releases growth hormone
3. Growth hormone then acts on the liver
4. The liver the produces IGF (which control metabolism and growth of bones)
5. When levels of GH are low, the hypothalamus produces more GHRH

121

What are the effects of growth hormones on respective cells in the body?

On adipose tissues
1. Lipolysis: break down of triglycerides into fatty acids (increased)
On liver
1. Glucogenesis: stimulates breakdown of glycogen thus releasing glucose into bloodstream (increased)
2. Stimulates the production of IGF and IGF binding protein (which makes the IGF more stable once bound)
a) Encourages somatic cell growth
b) Encourages growth of chondrocytes
c) Increases amino acid uptake thus increases protein synthesis in muscle cells
3. Muscle
a) Increases amino acid uptake thus increases protein synthesis in muscle cells

122

How does low blood glucose affect levels of growth hormone?

1. Low levels of blood glucose (hypoglycaemia) stimulates hypothalamus to secrete GHRH
2. GHRH stimulates the somatotrophs of the pituitary gland to produce GH
3. GH stimulates the secretion of IGF
4. IGF speeds up breakdown of glycogen into glucose
5. This causes blood glucose to increase
6. Increase in glucose above normal level stops the release of GHRH

123

How does high blood glucose affect levels of growth hormone?

1. High levels of blood glucose (hyperglycaemia) stimulates hypothalamus to secrete GHIH and inhibits GHRH
2. GHIH inhibits the somatotrophs of the pituitary gland from producing GH
3. Low levels of GH and IGF slows breakdown of glycogen in liver
4. Glucose is release into blood more slowly
6. Decrease in glucose below normal level stops the release of GHIH

124

What are the long term effects of growth hormone?

1. Stimulates proliferation of cartilage in epiphyseal plate of long bones before they fuse (great effect on linear growth)
2. Increases bone mass and increased mineral content of bone
3. Increases lean body mass (reduce adiposity by lipolytic effect)
4. Increases organ size and function

125

What are features of IGF?

1. Has two forms:
a) IGF 2: foetal
b) IGF 1: post natal
2. It's biological effects are modulated by IGF binding protein
3. IGF 1 feedback regulates GH
4. Has metabolic functions and increases cellular proliferation

126

Describe how IGF act on cells

1. IGF contains two receptors
2. IGF binds to receptor and causes receptor dimerisation
3. This binding then triggers the JAK (Janus Kinase) tyrosine kinases and intracellular portion of receptor
3. This causes auto phosphorylation (phosphate added to JAK and to receptor)
4. Phosphorylated JAK then phosphorylates STAT-P (signal transducer and activator of transcription)
5. STAT-P then translocates to the nucleus where they act on the nucleus and initiate transcription by activating transcription factor such as Pit-1

127

What are the features of thyroid gland?

1. Average weight of 34g
2. Hyperthyroid can lead to thyroid cancer
3. Hyperthyroidism can also lead to goitre
a) Just increase in thyroid tissue
b) Increase in thyroid tissue and increase in thyroid hormones
4. Has two loves located on each side of the trachea (4cm in length and 2cm thick)
5. Connected to each other by as isthmus (connective tissue)

128

How are thyroid hormone produced?

1. Required iodisation of tyrosine molecules (easily occurs on tyrosine molecules)
2. Iodine is however rare thus the thyroid gland traps these molecules and keeps reserves
a) Daily intake: 150microgram
b) Used by thyroid gland: 125 microgram
3. Iodine is obtained from seawater, seafood, fruit and vegetables
4. Spherical sacs called thyroid follicles make up most of the thyroid gland
5. Inside the thyroid follicles, iodide ions are incorporated into thyroglobulin
6. Thyroglobulin the gets cleaved into T3 and T4
7. Ratio of T4 to T3 is 20:1 but T3 is is more potent

129

Why is thyroid hormone important?

1. Acts on most cells of the body
2. Normal growth requires normal amounts of thyroid hormone
3. If T4 decreases before puberty then skeletal growth stops
4. Deficiency
a) Short stature
b) Delayed skeletal maturation
5. Excess
a) Increase of osteoblastic bone resorption
b) Increased bone loss

130

How are levels of thyroid hormone regulated?

Positive and negative feedback loops

131

Describe the process of regulating thyroid hormone

1. When levels of T3 and T4 are low in the blood, hypothalamus activates thyrotropin releasing hormone (TRH)
2. TRH then acts on the anterior pituitary gland which then secretes thyroid stimulating hormone (TSH) which targets the thyroid gland
3. Thyroid gland in turn releases T3 and T4
4.

132

What is the amount of thyroid hormone secreted daily?

100 microgram

133

How are thyroid hormones transported to the cells?

1. About 70-75% of T3 and T4 become attached to thyroid binding globulins upon entering the blood stream
2. Only relatively small quantities of thyroid hormones remain unbound
*however it is the unbound thyroid hormones that are active and are able to enter cells

134

How does thyroid hormone enter the cell and cause an effect?

1. T3 and T4 are lipid soluble and thus are able to cross the plasma membrane into the interstitial fluid
2. Once in the cytoplasm, all T4 are converted to T3 (by removal of one iodine)
3. T3 then diffuses into the nucleus where it binds to its receptor
4. The receptor is the a new to bond to region of the promoter and initiate transcription

135

What are the functions of thyroid hormone?

1. Stimulates metabolic rate
2. Increases number and size of mitochondria
3. Stimulate the use of cellular oxygen to produce ATP
4. Stimulate synthesis of respiratory chain enzyme
5. Increase membrane sodium/potassium ATPase concentration
6. Increase membrane sodium and potassium permeability (which increases metabolic rate as cells energy is spent maintains electrochemical gradient)

136

What are the signs of hyperthyroidism?

1. Intolerance to heat
2. Weight loss
3. Fatigue

137

What are the signs of hypothyroidism?

1. Intolerant to cold
2. Lethargic
3. Weight gain
4. Cool dry skin

138

How does thyroid hormone affect bone?

1. Thyroid hormones is needed for normal bone growth and development
2. Hyperthyroidism:
a) Enhanced bone formation coupled with increase bone resorption
b) TH stimulates both osteoblast an osteoclasts thus bone is formed and resorbed
3. Hypothyroidism:
a) Causes short stature in children

139

How does insulin work?

1. Insulin is released by the cell from storage granules
2. Insulin binds on insulin receptor on plasma membrane of cells
3. Binding of insulin activates kinases that creates multiple effects in the target cells:
a) Accelerate glucose uptake by increasing glucose transport protein in cell membrane (Glucose Transporter 2)
b) Accelerate utilisation of glucose and ATP production
c) Stimulates formation of glycogen (when glucose is in excess)
d) Stimulate absorption of amino acid and protein synthesis thus aiding growth
e) Stimulate formation of triglycerides in adipose tissues

140

Where are insulin receptors present and absent?

Present:
1. Liver
2. Muscles
3. Adipose tissues
Absent
1. Brain cells (take up glucose on their own)

141

What are features of insulin?

1. Produced by pancreatic beta cells
2. Lowers blood glucose levels
3. Synthesised as pro insulin and gets cleaved into insulin and c peptide > it is then packaged in vesicles
4. Consists of two peptide chains joined by disulphide bonds
5. It is anabolic: part of metabolism where simple structures are made into complex structures by promoting growth of tissues

142

How do cells adapt in response to a disease?

They undergo change in their cellular growth pattern
1. Change in size of cells (atrophy vs hypertrophy)
2. Change in number of cells (hypoplasia vs hyperplasia)
3. Change in differentiation

143

What is cell atrophy?

1. When there is decrease in cell size
2. May be achieved by apoptosis
3. Amongst its causes are:
a) Reduced functional activity
b) Loss of innervation
c) Reduced blood supply
d) Diminished nutrition
e) Loss of hormonal or growth factor stimulation

144

Distinguish physiological atrophy with pathological atrophy

Physiological
1. Thymus gland involutes during adolescence
2. Testis atrophies with age due to reduction in gonadotropins
Pathological
1. Atrophy of skeletal muscle after immobilisation (due to fracture)
2. Atrophy of thyroid gland due to prolonged inflammatory process (Hashimoto's disease)

145

What are features of cell hypertrophy?

1. Increase in size of existing cells accompanied by increase in functional capacity
2. Seen particularly in permanent cells as they are unable to make copies of themselves
3. Eg: left ventricular muscle fibres increase in size (hypertrophy) when aortic valve is narrowed of when systemic blood pressure is high

146

How are number of cells changed?

1. Hypoplasia: decreased number of cells
2. Hyperplasia: increased number of cells
a) Caused by increased cell division
b) Seen only in labile/stable cells (not permanent)
c) Often in response to hormonal influences

147

What is metaplasia?

1. An adaptive response to environmental stimuli
2. Specialised cell types changes their pattern of differentiation to a new mature stable cell type
a) Bronchus: columnar ➡️ squamous ⚠️ cigarette smoke
b) Cervix: columnar ➡️ squamous ⚠️ HPV and vaginal acid
c) Oesophagus: squamous ➡️ columnar ⚠️ acid juices
d) Stomach: gastric ➡️ intestinal ⚠️ inflammation
e) Bladder: transitional ➡️ squamous ⚠️ stones and parasites

148

What is neoplasia?

1. Abnormal uncoordinated tissue growth after the initiating stimulus has been removed
2. A neoplasm is a lesion resulting from such growth (often referred to as a tumour)

149

What is oncogenesis?

1. Process giving rise to development of neoplasia
2. Factors causing it are often referred to as carcinogens
3. Most carcinogens act on the DNA of individual cells

150

What are the different genes involved in controlling cell growth?

1. Oncogenes promote cell proliferation
2. Tumours suppressor genes inhibit cell proliferation
3. Mismatch repair genes maintain the integrity of cellular DNA

151

What are the 3 main categories of carcinogens?

1. Chemical
a) Rubber and dyes: bladder cancer
b) Cigarette smoke: lung cancer
2. Radiation
a) UV radiation: skin cancer
b) Ionising radiation: thyroid cancer
3. Viruses
a) Epstein Barr virus: lymphoma
b) HPV: cervical cancer
c) Hep B: liver cancer

152

Describe the multiple step of carcinogenesis

1. Neoplastic transformation arises as a result of accumulation of genetic damage
a) DNA genetic damage may be inherited as germline mutation
b) DNA damage may occur as a result of exposure to environmental agents
2. As tumour progresses, genetic damage accumulates
3. Abnormal cells are able to survive (would previously have been eliminated)
4. Abnormal cells proliferate
5. Eventually invade surrounding tissue
6. Later spread to other parts of the body

153

List the two ways of classifying tumour

1. Usually on basis of presumed cell/tissue of origin
a) Epithelial
b) Connective tissue (mesenchymal)
c) Lymphoid/haematological
d) Mixture of all (teratomas)
2. Predicted behaviour

154

List the tumours of epithelial origin

1. Squamous cell
B: papilloma
M: carcinoma
2. Glandular
B: adenoma
M: adenocarcinoma
3. Transitional
B: transitional cell papilloma
M: transitional cell carcinoma
4. Basal
B: basal cell papilloma
C: basal cell carcinoma

155

List the tumours of mesenchymal origin

1. Smooth muscle
B: leiomyoma
M: leiomyosarcoma
2. Striated muscles
B: rhabdomyoma
M: rhabdomyosarcoma
3. Blood vessels
B: haemangioma
M: angiosarcoma
4. Nerves
B: neurofibroma
M: neurofibrosarcoma
5. Adipose tissue
B: lipoma
M: liposarcoma
6. Cartilage
B: chondroma
M: chondrosarcoma
7. Bone
B: osteoma
M: osteosarcoma
8. Melanocytes
B: naevus
M: melanoma

156

What are the mesenchymal tumours that do not have a benign form?

1. Lymphoid cells: lymphoma (malignant)
2. Haematopoietic cells: leukaemia (malignant)

157

What are features of benign tumour?

1. Generally slow growing
2. Remain localised
3. Do not invade surrounding tissue
4. Do not spread to distant sites
5. Resembles tissue of origin (well differentiated)
6. Mitotic activity is low
7. Mitotic figures appear normal
8. Nuclei appears normal
9. No necrosis

158

What are features of malignant tumour?

1. Generally rapid growing
2. Irregular edges, poorly defined margins
3. May not resemble tissue of origin (poorly differentiated)
4. High mitotic activity
5. Abnormal mitoses
6. Nuclei are hyper chromatic and pleumorphic
7. Invade into surrounding tissues
8. Spread via lymphatic channels to lymph nodes
9. Spread via blood steam to other organs (metastasis)
10. Spread across body cavities

159

What are the effects of benign tumours?

1. Damage tissue by pressure effect
2. Block duct such as pancreas or bronchus
3. Block flow of fluid in brain
4. May secrete hormones
5. May become malignant

160

What are the effects of malignant tumour?

1. Destruction of adjacent tissue causing pain and loss of function
2. Pressure on structures leading to infection
3. Haemorrhage from surface ulceration
4. Obstruction of flow through vital structures
5. Secondary deposits causing damage at distant site
6. Cachexia (wasting) due to tumour necrosis factor alpha
7. Production of hormones either appropriate or inappropriate
8. Paraneoplastic syndrome (when multiple syndrome are present due to factors produced by tumour but the tumour hasn't spread)

161

What is metastasis?

1. Process by which neoplastic cells from the primary tumour spread to distant sites
2. Involves primary tumour invasion into surrounding tissues especially vessels (lymphatic or blood)
3. They then detach within the vessels and gets transported as emboli
4. They then undergo extravasation where by they move from vessel to to side and grow at distant site
5. Lymphatic spread leads to lymph nodes involvement

162

What are the four common sites of metastasis via blood?

Haematogenous metastasis
1. Lungs
2. Liver
3. Bone
4. Brain
*in order to metastasise they must possess cell surface receptor

163

What does stage and grade of tumours refer to?

Stage: how far a tumour has spread at time of presentation
Grade: how closely tumours resembles their tissue of origin

164

What is the system used to predict prognosis of colorectal tumours?

1. Dukes A: 90% 5 years (confined to bowel wall)
2. Dukes B: 66% 5 years (outside bowel wall but negative lymph nodes)
3. Dukes C: 33% 5 years (positive lymph nodes)

165

What does each letter in TNM system stand for?

T: primary tumour size
N: lymph node involvement
M: distant metastases

166

What are the 3 changes that occurs as cancer develops?

1. Increased cell division
2. Cell survival/immortalisation
3. Cell growth

167

How does the level of cyclin B fluctuate during cell cycle?

1. Low in the vast majority of interphase
2. Increases around G2
3. Peaks at transition between G2 and mitosis
4. Collapses at anaphase

168

What is the function of cyclin B?

1. Cyclin B binds to Cyclin Dependant Kinase 1 (CDK 1)
2. As Cyclin B peaks at transition between G2 and mitosis, CDK1 is only active during G2 > mitosis

169

What is the function of CDK1?

1. CDK1 is a kinase thus it adds phosphate to other proteins
2. CDK1 phosprylates
a) Histone 1: phosphorylation causes chromosome condensation
b) Microtubule Associated Protein (MAP): phosphorylation causes spindle formation
c) Lamin: phosphorylation causes breakdown of nuclear envelope

170

What are the different Cyclin/CDK combination in each stage of the cell cycle?

1. To start G1: Cyclin D and CDK4
2. To start S2: Cyclin E and CDK2 (allows production of protein necessary for DNA synthesis)
3. During S2: Cyclin A and CDK2 (sustains the process of protein synthesis)
4. To start mitosis:
a) Cyclin A and CDK1
b) Cyclin B and CDK1

171

Distinguish necrosis and apoptosis

Necrosis: accidental cell death due to injury which releases cellular content leading to an inflammatory response
Apoptosis: the organised destruction of cell which is initiated by either a signal from a neighbouring cell or the cell itself due to sensed internal damage. This process does not cause and inflammatory response and is commonly referred to as programmed cell death

172

How does extracellular signals induce apoptosis?

1. TNFalpha and FAS binds to receptor on the cell
2. This leads to formation of Death Induced Signalling Complex (DISC)
3. Once DISC is assembled it will activate a series of proteases (caspases)
4. Caspases will destroy the cell by dismantling the cell into loads of different components

173

How does intracellular signals induce apoptosis?

1. The cell recognises it has DNA damage or oxidative damage etc
2. Intracellular signals cause Bax to undergo a conformational change causing it to accumulate around the outer membrane of mitochondria
3. Once Bax has surrounded the outer membrane of mitochondria it will form a pore that allows protein sitting in between the outer and inner membrane of the mitochondria to escape
4. Those proteins are
a) Cytochrome C
b) Smac
c) Diablo AIF
5. Release of cytochrome C leads to caspases which causes apoptosis of the cell

174

What is the effect of Myc on cell growth?

1. Reducing Myc function decreases cell size
2. Increasing Myc function leads to enlarged cell

175

What are the genetic changes that leads to colon cancer?

1. Normal
⚠️ Loss of APC
2. Tubular adenoma
⚠️ Activation of k-Ras or BRAF
3. Villus adenoma
⚠️ Loss of TGFbeta RII or SMAD4
⚠️ Loss of p53
4. Invasive carcinoma
⚠️ Activation of PRL-3

176

What are proto-oncogenes?

1. Promote cell division, survival and growth
2. Protein function is increased by mutation
a) Missense mutation that increases enzyme function
b) Gene amplification leading to over expression of protein
3. Activated form is known as oncogene
4. Dominant mutation
⚠️ k-Ras
⚠️ PRL-3

177

What are tumour suppressor genes?

1. Inhibit progression through cell cycle
2. Promote cell apoptosis
3. Inhibit cell growth
4. Protein function reduced by mutation
a) Deletions that remove the gene
b) Nonsense protein that truncate the protein
5. Recessive mutation
⚠️ APC
⚠️ P53

178

Describe what happens in absence of Wnt ligand

1. Wnt pathway is important to maintain stem cells in the colon and also for their differentiation into other cells
2. In abscence of Wnt ligand, you get a complex of
a) APC
b) Axin
c) Glycogen synthase kinase (GSK)
3. The complex adds phosphate to a Beta Catenin which causes Beta Catenin to be degraded
4. Without Wnt signalling the levels of Beta Catenin in a cell is low due to constant degradation by the complex

179

Describe what happens in presence of Wnt ligand

1. In the presence of Wnt ligand it binds to the receptor (one of the receptor is known as Frizzled)
2. That causes the complex to bind to Dvl (dishevelled) and becomes deactivated
3. As a result phosphate can no longer be added to Beta Catenin and its degradation is prevented
4. Thus the levels of Beta Catenin goes us massively
5. When the level is high Beta Catenin can also get into the nucleus where it binds to T Cell Factor (TCF) and drives transcription
6. This occurs in a controlled manner to promote cell division

180

How does lack of APC affect the Wnt signalling pathway?

1. Without APC we lack the destruction complex
2. Thus you can't phosphorylate Beta Catenin
3. This leads to accumulation of uncontrolled Beta Catenin (constant high levels)
4. This then causes constant transcription of genes
5. In the colon those genes are
a) Cyclin D: drive cells into cell cycle
b) Myc: increase cell size
6. In other words the cell are constantly dividing and gaining bulk

181

What are the features that a successful cancer cell must possess?

Become
1. Independent of external growth signals
2. Insensitive to external anti-growth signal
3. Able to avoid apoptosis
4. Capable of indefinite replication
5. Capable of sustained angiogenesis
6. Capable of tissue invasion and metastasis

182

How many successive events is required to convert a normal cell to a malignant cell?

4-7 events

183

How do we get cancer?

1. Theory 1
Mutation that increases the rate of cell proliferation so as to provide an expanded target for subsequent mutation
2. Theory 2
Mutation that destabilise the genome so as to increase the subsequent mutation rate

184

What are the two genomic instability shown by common cancer?

1. Chromosomal instability
a) Bizarre karyotype
b) Many numerical and structural abnormality
2. Microsatellite instability
a) High frequency of sequence errors after DNA replication

185

What are the two types of cancer?

1. Familial cancer
2. Sporadic cancer

186

What are features of familial cancer?

1. Single gene or Mendelian disorders
2. Most are inherited as autosomal dominant trait
3. Most due to inherited mutation of tumour suppressor genes
4. Further genetic events are necessary in somatic cells
5. 1% of all cancers
6. Increased cancer susceptibility
7. May be associated with multiple tumour types
8. May be associated with other abnormalities

187

What are features of sporadic cancer?

1. 99% of all cancers
2. Due to exposure of carcinogenic agents and unrepaired DNA replication errors
3. Results in somatic activation/inactivation of cancer genes

188

Distinguish oncogenes and tumour suppressor genes

1. Oncogenes
a) Gain of function
b) Dominant
c) Only one copy of the gene needs to be activated
2. Tumour suppressor gene
a) Loss of function
b) Recessive
c) Both copies of the gene needs to be activated

189

What are some of the oncogenes commonly associated with cancer

1. Secreted growth factor
⚠️ EGF
⚠️ PDGF
2. Cell surface receptor
⚠️ EGFR
3. Signal transduction system component
⚠️ ABL
4. Nuclear proteins and transcription factors
⚠️ MYC
⚠️ FOS
⚠️ JUN
5. Cyclins/Cyclin dependant kinase
⚠️ Cyclin D1
⚠️ CDK4

190

What oncogenes are over expressed in oral cancer?

⚠️ EGFR
⚠️ Cyclin D1
⚠️ Myc

191

How does Burkitt's lymphoma occur?

1. Myc from Chromosome 8 is translocated to Chromosome 14 (next to immunoglobulin gene)
2. Whenever the immunoglobulin genes are expressed you also express Myc inappropriately

192

How does chronic myeloid leukaemia occur?

1. Chromosomal 9 and 22 are translocated thus producing a chimaeric gene
2. This gene then encodes an overactive growth signalling molecule
3. Does not respond to the normal mechanism that would stop the production of protein

193

What are the 3 main function of tumour suppressor gene?

1. Anti proliferative
⚠️ CDKN2A
⚠️ Retinoblastoma (Rb)
2. Pro apoptotic
⚠️ TP53
3. DNA repair and genome stability
⚠️ MSH2
⚠️ MSH6
⚠️ TP53
⚠️ BRCA1

194

How does retinoblastoma regulate cell cycle?

1. G1 is the check point where cells decide if it wants to divide or not
2. E2F1 is a transcription factor that causes signalling of genes necessary to enter the S phase
3. If retinoblastoma is bound to E2F1, it is unable to tell the cell to divide
4. Retinoblastoma can only bind to E2F1 if it is under phosphorylated
5. If it is phosphorylated it won't bind to E2F1 and cell cycle will carry on
6. Phosphorylation of retinoblastoma is controlled by Cyclin D and CDK4

195

What causes inactivation of tumour suppressor gene?

1. Mutations
2. Chromosomal abnormality
3. Methylation of promoter
4. Interaction with viral protein (HPV inhibits Rb)

196

Distinguish the effect of mutated tumour suppressor gene in both familial cancer and sporadic cancer

Familial cancer
1. Early onset
2. More than 1 tumour of the same type
3. Other types of tumour may be present
4. In tumour cells: both copies of TSG are inactivated
5. In all other cells: one copy of TSG is inactivated
Sporadic cancer
1. Later onset
2. Single tumour usually
3. No other tumours usually
4. In tumour cells: both copies of TSG are inactivated
5. In all other cells: normal

197

What are features of Familial Adenomatous Polyposis

1. Mode of inheritance: autosomal dominant
2. Gene mutated: ⚠️ APC
3. Incidence: 1: 8000 - 10000
4. Colonic features
a) Multiple polyps (adenoma) develop usually after puberty
b) One or more polyps transform into adenocarcinoma usually in 3rd/4th decade
5. Extra colonic features
a) Dento osseous change
b) Congenital hypertrophy of retinal pigmentary epithelium
c) Desmoids
d) Sebaceous cyst
d) Extracolonic polyposis and carcinoma

198

What are the genetic changes in Familial Adenomatous Polyposis?

1. Inherited germline mutation of one copy of APC
2. Somatic mutation of second APC allele
3. Occurs early in the multistage process
4. Leads to multiple polyps (adenomas)

199

What are the genetic changes in sporadic colorectal cancer?

1. Somatic mutation of one copy of APC allele
2. Somatic mutation of second APC allele in the clone of cells carrying the first hit
3. Leads to single polyp (adenoma)

200

What are the origins of genetic errors?

1. Errors in replication
2. Exposure to genotoxic environment

201

What are the two nature of genetic changes?

1. Gross (at chromosomal level)
a) Numerical abnormality: aneuploidy, polyploidy
b) Structural abnormality: single/two chromosomes
2. Subtle (at molecular level)
a) Mutation: structural change in the sequence
- Single base (point mutation)
- Larger segments of DNA
b) Promoter methylation: addition/removal of methyl groups to specific nucleotides in the promoter region of genes to regulate expression of genes

202

What are the types of point mutation?

1. Truncating mutation (wrong size or no protein made)
a) Nonsense: premature stop codon
b) Frameshift insertion/deletion: deletion or insertion of one base that changes the triplet reading frame
c) Splice site mutation: where a splice site is abolished or a new one is created
2. Non truncating mutation
a) Missense mutation: one amino acid is replaced with another
b) Silent mutation: does not result in replacement of one amino acid with another

203

What are the STOP codons on mRNA and the DNA base sequence they produce?

UAG ➡️ TAG
UAA ➡️ TAA
UGA ➡️ TGA

204

What are intron and exons?

1. Genes are divided into
a) Intron: junk DNA
b) Exon: codes for protein
2. Initially when mRNA is transcribed from DNA, the introns are also transcribed
3. Soon a splicing machinery processes the mRNA and splices out the introns
4. The exons are then joined together
5. The splicing machinery has the ability to recognise bases at intron/exon interphase
a) GT at the beginning of an intron
b) AG at the end of an intron

205

What are the results of abnormal splicing in following sequence (Exon1 ➡️ Intron1 (with splice site mutation) ➡️ Exon2 ➡️ Exon3)

1. Intron1 is included in the sequence
a) Exon1 ➡️ Intron1 ➡️ Exon2 ➡️ Exon3
b) During protein synthesis Intron1 will be read until an unnecessary stop codon is read which then stops protein production
2. Skipping of Exon2
a) Exon1 ➡️ Exon3
3. Use of alternative (cryptic) splice sites in Intron1
a) Exon1 ➡️ Intron1 {partial} ➡️ Exon2 ➡️ Exon3
4. Use of alternative (cryptic) splice sites in Exon2
a) Exon1 ➡️ Exon 2 {partial} ➡️ Exon3

206

What factors determine the effect of missense mutation?

1. How different the substituted amino acid is to the intended amino acid
2. How important the amino acid is for the function of the gene product

207

What is trinucleotide repeats?

1. Trinucleotide repeat sequence (CAG)n occur relatively common in the human genome
2. However repeat sequence beyond a certain length can be unstable
3. Expansion of repeat sequence within or in the vicinity of genes can cause disease

208

What are the two classes of expansion of trinucleotide repeats?

1. Genes with modest expansion of (CAG)n repeats within coding region
a) Stable alleles: 10-30 repeats
b) Unstable alleles: 40-200 repeats
c) Result in long polyglutamine tracts within the protein causing it to aggregate within cells and kill them
2. Genes with very large expansion of repeat sequence in non coding region
a) A variety of triplet sequence (CGH, CCG etc)
b) In promoter or intronic region
c) Stable alleles: 5-50 repeats
d) Unstable alleles: >100 repeats
e) Results in inhibition of gene expression of aberrant splicing

209

In Huntington's disease what is the number for CAG copies needed to cause the disease?

Normal function: 10-35
Incomplete penetrance: 36-39
Full penetrance: >40

210

How are genes switched on and off?

Gene transcription can be switched off by methylation of nucleotide bases particularly cytosine in their promoter region

211

What is epigenetic change?

1. Hyper methylation: inappropriate switching off of affected gene
2. Hypo methylation: inappropriate switching on of affected gene
*however methylation is a normal mechanism for regulating the expression of genes (X chromosome in women)

212

What are the effects of genetic alteration in nuclear DNA and mitochondrial DNA?

Nuclear DNA
1. Mendelian inheritance
2. Wide range of phenotypes
3. Wide range of tissue affected
Mitochondrial DNA
1. Maternal inheritance
2. Restricted phenotype
3. Specific tissues affected
4. Highly variable severity

213

What are the effects of genetic alteration in the germ cells and somatic cells?

Germ cells
1. Transmitted through germline
2. Sometimes not passed on to offspring as it is lethal
Somatic cells
1. Restricted to individual
2. Thus it exist as a restricted somatic disease
3. May present itself
a) Early: during embryogenesis thus the individual ends up with significant clone of mutant cells)
b) Late: gives the cell a growth advantage thus leads to formation of tumours)

214

What is the effect of GNAS1 mutation?

1. Somatic
a) Early: McCune Albright Syndrome
b) Late: fibrous dysplasia, isolated endocrine lesion
2. Germline: lethal

215

What is the effect of genetic alteration is critical and non critical region of DNA?

1. Non critical:
a) Little effect
b) No effect
2. Critical
a) Lack/reduced synthesis
b) Non/reduced function
c) Altered function

216

What are the effect of mutation on protein?

1. Loss of function
a) Failure of synthesis
b) Non functional protein
2. Gain of function
a) Inappropriate/over synthesis
b) Functionally abnormal protein
c) Protein with novel function

217

What are features of loss of function mutation?

1. Traits
a) Generally recessive
b) Sometimes dominant
c) Somtimes are dominant negative
d) Sometimes dosage related
2. Mutations tend to be varied
3. Results in loss of function of protein due to any of the following
a) Failure of synthesis of protein
b) Synthesis of non functional protein

218

What are features of gain of function mutation?

1. Generally dominant
2. Mutation tend to be specific
3. Results in gain of function of protein due to any of the following:
a) Inappropriate synthesis of protein
b) Over synthesis of protein
c) Synthesis of protein with abnormal function
d) Synthesis of protein with novel function (very rarely)