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CSIM > Genetics > Flashcards

Genetics Flashcards

1
Q

DNA structure

A

Deoxyxribrosenucleic acid. Double strand helix. Phosphate back bone chains lie in antiparallel. With complementary nucleic acids held together by weak hydrogen bonds.

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2
Q

DNA replication

A

Strands are separated by DNA helices, replication fork is formed with DNA polymerase. Leading strand formed continuously, with lagging strand made up of short okazaki fragments joined by DNA ligase

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3
Q

satellite DNA

A

repetitive DNA sequences very large series of simple repeats transcriptively inactive and clustered around centres of centromeres

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4
Q

Mitochondrial inheritance

A

derived from oocyte - maternal

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5
Q

Introns vs exons

A

Introns are non coding and spliced out

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6
Q

Transcription

A

DNA to RNA. Uracil instead of thymine. DNA unzipped by RNA polymerase allowing complementary RNA nucleotides to bond to the DNA forming antisense RNA strand

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7
Q

Complementary base pairs

A

A to T, C to G

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8
Q

Post-transcription modification

A

Poly A tail
non coding introns spliced out
5’ adenyl cap

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9
Q

Translation

A

Production of proteins from mRNA strand. mRNA travels to the ribosome. Promoter regions tell 30s and 50s subunits of the ribosomes to bind. tRNA molecules have an amino acid preloaded and bind to their complementary triplet codon. Peptyltransferase forms the polypeptide chain until stop codon reached

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10
Q

DNA code

A

Non overlapping, degenerate

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11
Q

Polymorphisms

A

variation in genetic code with no effect on phenotype

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12
Q

Somatic vs germline mutations

A

Somatic - sporadic adult onset no passage to offspring

Germline - passes to offspring. Predisposed to cancer 2 hit hypothesis

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13
Q

Substitution mutation

A

replacement of a single nucleotide.

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14
Q

Deletion and insertion

A

If not in multiples of 3 will lead to frame shift. Frame shift leads to complete change of amino acid sequence, can lead to early or late stop codons

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15
Q

Autosomal dominant

A

Manifests in heterozygotes. Only one mutant allele needs for expression. 50% passage to offspring. Seen in pedigree by male to male passage and about 50% of relatives affected

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16
Q

Pleuritropy

A

single gene leads to two or more unrelated effects in different body systems

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17
Q

Variable expression

A

different manifestations of disease in individuals with the same genetic condition

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18
Q

Penetrance

A

proportion of individuals with a genetic mutation who exhibit signs and symptoms of the disorder

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19
Q

Autosomal recessive

A

only manifest in homozygous individuals i.e. 2 copies of the defective allelle

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20
Q

EBV and cancer

A

Burkitts, craniopharyngioma, Hodgkin lymphoma

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21
Q

Proto-oncogenes

A

Promote cellular proliferation active during embryonic life and during tissue repair. Usually inactive

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22
Q

Oncogene

A

Mutated proto-oncogene capable of production uncontrolled cell division

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23
Q

RET (inactive)

A

Helps neural crest cells form the myenteric plexus in the gut. If inactive oncogene leads to absence of the parasympathetic ganglion cells in the gut = Hirschprungs

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24
Q

Hirschprungs PC

A

Often failure to pass meconium at birth, abdominal distention. Narrowing of sigmoid colon. May present later in life with FTT, chronic constipation and abdo distention.

Biopsy of myenteric plexus showing absence of ganglion cells. Mx = surgery

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25
Q

RET (active oncogene)

A

MEN 2 is due to a mutation in RET proto-oncogene, a tyrosine kinase receptor on cr 10. Leads to constant activation

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26
Q

MEN 2A

A

Medullary thyroid cancer, phaechromocytoma, parathyroid hyperplasia

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27
Q

MEN 2B

A

Marfanoid body habits, mucosal neuromas, medullary thyroid and phaechromocytoma

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28
Q

Tumor supressor genes

A

Designed to arrest cell growth, the brakes on the cell cycle

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29
Q

Rb

A

Tumour supressor gene which when mutated leads to retinoblastoma. Rare highly malignant childhood cancer developing from the retinal cells of the eye

  • sporadic = unilateral
  • heridatry = bilateral

PC = abnormal appearance of retina when viewed though pupil. Red reflex tested at birth, white reflex

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30
Q

Li Fraumeni

A

Mutation in p53. Guardian of the genome AD can give rise to leukaemia, osteosarcoma, early onset breast, brain and adrenal cancer

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31
Q

Colorectal Ca

A

Intestinal crypt cells are key to the initial event. 10% due to hereditary cause.

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32
Q

Mutator pathway

A

Mutator gene which allows other genes to gather mutations, this prevents recognition and repair. Increasing number of mutations confers malignancy

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33
Q

Lynch (HNPCC)

A

AD condition in DNA mismatch repair leading to huge numbers of polyps in proximal colon. 80% penetrance @ 40-60y/o

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34
Q

Cancer risk in lynch syndrome

A

colorectal, endometrial, ovarian, gastric and duodenal adenomas

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35
Q

Amsterdam criteria

A

3 colorectal tumors in family
2 succesive generations
1 < 50yo

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36
Q

Microsatellite instability

A

Defective DNA mismatch repair leads to susceptibility to mutation. Mismatch repair acts to correct errors made within DNA replication. Failure to work correctly leads to accumulation of errors. Slippage of daughter strand when replicating leads to DNA polymerase cleaving small fragments - microsatellites

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37
Q

High micro satellite instability

A

Indicative of Lynch.

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38
Q

BRAF V600E

A

Driver mutation in 15% of sporadic CRC, rarely seen in Lynch syndrome

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39
Q

Mx Lynch

A

75mg aspirin OD
2 yearly colonoscopy for survillance. uterine USS
+ve FHx = 1-2 yr upper GI endoscopy
family cascade testing

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40
Q

Mair Torre

A

Lynch syndrome + sebaceous skin tumors

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41
Q

Turcot

A

Lynch + glioblastoma

FAP + medulloblastoma

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42
Q

FAP

A

1000’s of colonic adenomas. 100% penetrance by 40yo

Usually clinically silent occasionally may present with wt loss, anaemia or PR bleeding

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43
Q

FAP and APC

A

Loss of tumour suppressor gene responsible for producing adenomatous polyposis coli. AD. Attenuated APC has better prognosis with few polyps

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44
Q

Extracolonic manifestations

A

Desmoid tumours, gastric polyposis, papillary thyroid caner, congenital hypertrophy of retinal pigment epithelium

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45
Q

Mx FAP

A

genetic screening of family members
close colonic surveillance
prophylactic colectomy if 30+ advanced polyps detected

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46
Q

Cowdens syndrome

A

AD condition in PTEN1 tumour stressor gene gives rise to multiple bengin hamartomas found on the skin, mucous membranes, in the thyroid gland and breast tissue

Increased risk of breast, follicular thyroid and endometrial cancer

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47
Q

Peutz-Jeghers

A

AD conditon with presence of benign harmatous polyps in the GI tract and hyper pigmentation of the oral mucosa

Increased risk of GI, pancreatic, breast, uterine, testicular

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48
Q

CRC aetiology

A

80% sporadic, 20% familial with unknown causes of this 5% is thought to be attributable to lynch/FAP

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49
Q

Population CRC screening

A

one off flexisigmoidoscopy @ 55y/o

feacal occult blood 2 yearly from 60-74

50
Q

BRAF V600E +ve/ MSI

A

1 relative < 50 or 2 relatives 60 = 2yrly colonoscopy from 25 y/o

If -ve 5 yearly from 50y/o

51
Q

Diagnosing AD disorders

A

Clinical diagnosis, specific gene test i.e. FBN1 - Marfans,
suspected cause ? = gene panel, whole exome sequencing. Diagnosis from pedigree where gene testing may have been normal - new mutation

52
Q

De novo mutations

A

new mutations found in generations

53
Q

Anticipation

A

Using triplet repeats disorder is passed onto the next generation where it manifests at a younger age and is often more severe

54
Q

Genetic heterogenicity

A

Single phenotype may be caused by any one of a number of alleles

55
Q

Triplet repeat disorders

A

All demonstrate anticipation. Mutation causes and increased number of randomly repeated trinucleotides

56
Q

Huntingtons PC

A

AD disease which due to defects in the HTT gene leads to progressive brain cell death

PC chorea, restlessness, poor coordination, unsteady gait, difficulty speaking, insomnia, dementia, personality changes, reduced cognition

57
Q

Anticipation in Huntingtons

A

CAG repeats dictates the severity of the disease
< 26 = normal
27-35 = premutation, alleles confer worse prognosis for next generation
36-39 = reduced penetrance but symptomatic
40+ = fully penetrant

58
Q

Mx huntingtons

A

MDT, SALT, dietician, physio, tetrabenazine to reduce chorea

59
Q

Myotonic dystrophy

A

AD DMPK gene progressive muscle wasting and weakness, cataracts, arrhythmias, infertility, frontal balding, myotonia

> 2000 repeats onset in early childhood or incompatible with life

60
Q

Long QT syndrome

A

Predisposition to delay of depolarisation due to channelopathies leading to increased risk of tornadoes de points and VF. ECG shows QTc >440m/s

Displays genetic heterogeneity where many different gene mutations cause the same phenotype

61
Q

Marfan’s syndrome

A

Connective tissue disorder with reduced extracellular microfibril formation and disrupted elastic fibres. Demonstrates variable expression with different family members presenting with different presentations despite the same genetic condition

62
Q

Ghent criteria - major

A

Ectopic lentis
Dilation of aortic root/dissection of aorta
Lumbosacral ectasia - dural thickening may - back pain
Pectus cavinatum/excavatum
FBN1 mutation
Hypermobile joints - wrist and fingers

63
Q

Other signs of marfans

A

Archnodactyl, high arched palate, tall and skinny, mitral valve prolapse, spontaneous pneumothorax, myopia, cataracts, pes planus

64
Q

Genetics Marfans

A

AD approx 80% linked to FBN1 mutation - missense mutation resulting in extracellular matrix containing 35% less fibrin 1. 20% de novo mutation

65
Q

Mx Marfans

A

B-blocker to reduce dilation of aortic root
Prophylactic surgery of mitral valve/aortic root
Yearly echo

66
Q

NF1

A

1/3000 people skin pigmentation and growth of tumours on nerves skin and brain. AD 100% penetrance defect in NF1 gene which makes neurofibroma a tumour suppressor

67
Q

Diagnosis of NF1

A 
2 of the following criteria
>6 cafe au last spots
freckling @ inguinal region or axilla
optic glioma
Lisch nodules - brown translucent mounds on iris
>2 neurofibromatoms
68
Q

Complications of NF1

A

30% = nerve compression giving pain, weakness and parathesia
epilepsy
5% risk of optic glioma, astrocytoma and other malignant conditons

69
Q

Tuberous sclerosis

A

Rare condition with 75% of mutations occurring de novo

PC - facial rash of angiofibroma
hypomelanotic patches
fungal fibromas - raised nodules @ finger nails
retinal nodular hamartomas

Can lead to seizures, ADHD, poor IQ, renal failure and cysts, cardiac rhabdomyomas

70
Q

Non invasive prenatal diagnosis

A

Maternal blood sample sent to test for fetal DNA @ 8 weeks

71
Q

Preimplantation genetic diagnosis - PGD

A

Genetic profiling of embryos prior to implantation

72
Q

Spinal muscle atrophy

A

AR condition involving degeneration of anterior horn cells in spinal cord. Type I and II onset before 12 and are usually fatal before 6months. III and IV begin in adults and confer a better prognosis

73
Q

PC SMA

A

Progressive UMN and LMN weakness, focal asymmetry, dysphagia and dysarthria, fasciculation

74
Q

CF

A

Carrier incidence of 1/20 life expectancy of 42y/o. AR defect causing defective CFTR gene. This is responsible for a transmembrane chloride channel. Different mutations of the gene have effects from misfolding to complete dysfunction. A defective CFTR channels leads to increased Na+ movement from apical membrane to balance the intracellular charger. H20 follows the Na+ leading to sticky viscous mucus. Commonest is F508

75
Q

PC CF

A

Lungs - cilia are unable to waft the viscous mucus leading to recurrent infections - bronchiectasis, fibrosis and cor pulmonale. Risk of rare infections - pseudomonas, aspergillum

GI tract - thick mucus blocks pancreatic secretions leading to malabsorption syndromes and steatorrhea. Enzymatic destruction of the pancreas = DM
- Can present in children as meconium ileus/FTT

Males approx 95% infertile due to congenital absence of vas deferens.

76
Q

Chorionic villus sampling

A

Sampling of placental tissue and analysis with FISH/PCR. Earliest technique at 10-12 weeks
Risk of choriamnioitis, 1% of miscarriage, oligohydramnios

77
Q

Aminocentesis

A

Sample of amniotic fluid from 14-16wks. Lower risk of miscarriage. SE - chorioamniotis, preterm labour

78
Q

Fetal alcohol syndrome

A

PC microcephaly, smooth philtre, palpebral fissure, developmental delay, thin upper lip

79
Q

Tetragenic drugs

A

ACEi, warfarin, valproate, lithium, phenytoin, methotrexate

80
Q

Teratogenic infections

A

CMV - chorioretinitis, deafness
DM - 2-3x risk of congenital abnormalities, heart defects and neural tube
Rubella - 1st trimester PDA, pulmonary artery stenosis
Toxoplasmosis - hydrocephalus, microcephaly, cataracts

81
Q

Other teratogenic agents

A

radiation, alcohol, maternal illness - SLE

82
Q

Other teratogenic agents

A

radiation, alcohol, maternal illness - SLE

83
Q

Downs syndrome

A

Trisomy 21. Increased risk with maternal age. If increased nuchal translucency on USS.

Triple test of - PAPP-A, bHCG and USS

84
Q

PC Downs

A

hypotonia, sleepy, excessive nuchal skin @ newborn

facial - epicanthic folds, brushfield spots in eyes, protruding tongue, small ears, upward sloping palpebral fissures

limbs - singular palmar crease, wide 1st-2nd toe gap, small middle phalanx of 5th

Cardiac - congenital heart defects in 45%, VSD, PDA and tetralogy of ballot

Hirshcprungs and duodenal atresia

85
Q

Complications of downs

A

low IQ, increased risk of alzheimers and ALL, epileptic seizures, poor fertility, thyroid problems

86
Q

Genetics of Downs

A

94% full trisomy due to non disjuncture at meiosis

4% robertsonian translocation where hybrid chromosomes are formed of 2x long and 2x short arms
- this can be balance or unbalance (loss of genetic material)

2% mosacism. Non disjuncture @ mitosis. Often better prognosis higher IQ

87
Q

CHARGE syndrome

A 
Coloboma of eye
Heart defects
Atresia of choane - nasal passage narrowing
Retardation of development
GU abnormalities
Ear abnormalities and hearing loss
88
Q

Aneuploidy

A

Abnormal number of chromosomes

89
Q

Structural rearrangement

A

Balanced - no loss or gain of genetic material required karyotyping to detect as clinically silent. Increased risk of passage to offspring

Unbalanced - loss of genetic material leading to phenotype detectable on microarray

90
Q

Edwards PC

A

Trisomy 18. Only 5% survive to term - 3% live to 10y/o

PC - low birth wt, growth retardation, clenched fists overlapping fingers, small jaw and mouth, structural heart defects, oesophageal atresia, webbing of toes, cleft palate

91
Q

Translocations

A

transfer of genetic material from one chromosome to another.

Reciprocal = breakage of cr and exchange, identified via FISH

Robertsonian = breakage of atrocentric chromosomes - 13,14,15,21,22 close to centromeres

92
Q

Mosacism

A

2+ cell lines that differ in their genetic constitution but have the same genetic origin. Non disjuncture at mitosis

93
Q

Patau’s

A

Trisomy 13 80% live only 1 year.

PC - scalp defects, dextrocardia, low set ears, rocker bottom feet, micropthalmia, exomphalos, post axial polydactyl

94
Q

Turners Syndrome

A

45X - The only viable monosomy seen in 1/5000 female births

95
Q

PC Turners

A

PC short stature, webbed neck, widely spaced nipples, puffy feet and extremities at birth, small ears
All will have ovarian agnesis leading to ovarian failure at puberty - amenorrhea and infertility.
30 % horseshoe kidney, congenital heart defects - CoA,AS, thyroid problems

Mx = ostetrogen replacement

96
Q

Kleinfelters

A

47xxy 1/1000 males presence of an extra x chromosomes leads to low testosterone and female bodily characteristics

97
Q

PC 47xxy

A

Often becomes evident around puberty - gynecomastia, tall, thin, long legs, reduced muscle bulk, small testes and penis, hypogonadism

Mx = replace testosterone, CBT, counselling

98
Q

Complications of Kleinfelters

A

Learning difficulties, osteoporosis, VTE, subfertility

99
Q

Fragile X

A

Mutation @ FMR1 gene leads to increasing repeat sequences > 200 = fragile X, <200 = tremor, ataxia - premutation

100
Q

PC fragile X

A

Learning difficulties, facial features - high forehead, large, ears, long face, prominent jaw. ADHD, recurrent sinus infections and connective tissue problems

101
Q

FISH

A

Fluorescent in situ hybridisation uses probes to look for submicroscopic deletions. Therefore must know what disorders/ ares of DNA need to be targeted

102
Q

Whole gene sequencing

A

Whole genome is examined for single nucleotide polymorphism compared to reference. Huge amounts of data can = problems but can find everything

103
Q

Karyotyping

A

Looking at number of chromosomes down microscope to look for aneuploidy - translocations, big deletions and ring cr. Cant be used for genetic mutations smaller than chromosomal abnormalities.

104
Q

Di George syndrome

A

22q11.2 microdeletion seen in 1/40000 live births heart malformations, improper pharyngeal pouch formation

105
Q

PC Di George

A

underdevelopment of thyroid and parathyroid, defienciy in maturing T cells due to absence of a thymus, hypocalcemia, congenital heart defects - TOF

cleft palate, long face, small teeth, broad nose

Increased incidence of MH - schizophrenia, ADHD, autism

106
Q

Prader Willi

A

15q11q13 gene example of genomic imprinting. Normally paternally derived gene is expressed and maternal gene is silenced. Prader willi = deletion or mutation in paternal gene/ maternal uniparental disomy

107
Q

PC Prader Willi

A

@ birth - FTT, poor muscle tone and suck reflex

infancy - small hands, feet and eyes, hypothalamic dysfunction leads to over eating - obesity, DM, OSA, hypogonadism

108
Q

Genomic imprinting

A

Epigenetic process that involves the methylation of DNA/histone without altering the DNA sequence

109
Q

Angelman syndrome

A

15q11q13. Normally maternally derived with paternal chromosome being silenced. Therefore occurs due to a maternal deletion/mutation or nondisjuncture leading to inheritance of both paternal chromosomes

110
Q

PC Angelmans

A

PC = developmental delay, ataxia, speech impairment,extremely happy demeanour short attention span, seizures,

111
Q

Lyonisation

A

X chromosome inactivation. Dose compensation is crucial. Random X chromosome in females is inactive, can be skewed if a growth advantage is conferred.

112
Q

DMD PC

A

2-4y/o slowly progressive, muscle weakness, waddling gait, calf hypertrophy and thigh wasting, Gower’s sign = difficulty standing up uses objects to help push up.

Progression - wheelchair bound by 20y/o, scoliosis, dilated cardiomyopathy, resp failure due to weak diaphragm

113
Q

Dystrophin

A

Huge gene links intracellular actin and the extracellular matrix stabilising the sarcomere. In its absence the sarcomere is unstable and CK leaves, Ca2+ entry leads to muscle cell death and atrophy via water entering the mitochondria and causing them to burst. Gradually muscle is replaced with fat and fibrous tissue

114
Q

DMD vs BMD

A

DMD - mutation severe leads to nonsense/ frame shift mutation giving no dystrophin production

BMD - misshapen dystrophin due to inframe mutation

115
Q

X-linked disorders

A

Males cant pass the affected allele to males, daughter will always inherit the affected allele if her father is affected.

116
Q

Biopsy of DMD

A

degeneration of muscle fibres, hypertrophy of remaining muscle fibres, scattered chronic inflammatory cells. Absent sub-sarcolemma staining

117
Q

Robertsonian translocation

A

Two acrocenteric chromosomes join and the short arm is lost leaving only 45 Cr remaining. Despite loss of genetic material the translocation is balanced and the individual is healthy. Offspring are at risk of inheriting the unbalanced arrangement

118
Q

BMD PC

A

Calf hypertrophy, cardiomyopathy, raised CK, life expectancy 60 y/o

119
Q

Achondroplasia

A

AD conditon mutation in the FGFR3 gene, 80% cases are sporadic de novo mutations

PC = short stature, forehead bossing, flat nasal bridge, square hands, varus or valgus deformity, flaring at the end of long bones on X-ray

120
Q

Ataxia telengectasia

A

AR mutation in the ATM tumour suppressor gene. Increased incidence of lymphoma, leukaemia , facial telengestasia, frequent URTI and LRTI, progressive ataxia

121
Q

Von hippel lindau

A

AD mutation in the VHL tumour suppressor gene gives increased risk of clear cell renal cancer and phaechromocytoma

122
Q

Kallmans syndrome

A

Congenital GnRH deficiency. PC = total anosmia, cleft palate, unilateral renal agensis, small testicles, failure to start puberty, infertility

CSIM (12 decks)

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