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MRCOG part 1 > Clinical genetics > Flashcards

Clinical genetics Flashcards

1
Q

What are nucleotides made up of

A

Sugar molecule, nitrogenous base, phosphate group.

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2
Q

What does the nucleotide sugar molecule look like?

A

5 carbon atoms, pentose ring.
DNA = deoxyribose
RNA = ribose

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3
Q

Where is the base attached on the sugar of a nucleotide?

A

on carbon 1

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4
Q

Where is the phosphate attached on the sugar of a nucleotide?

A

carbon 5

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5
Q

How many types of nitrogenous base are there and what are they called

A

purines and pyrimidines

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6
Q

Purines are…

A

Purines - Guanine, Adenine

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7
Q

Pyrimidines are..

A

Pyrimidines - Cytosine and Thymine (DNA) or Uracil (RNA)

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8
Q

Nucleic acids

A

Long nucleotide chains - DNA (ds) RNA (ss)

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9
Q

DNA

A

ds helix held together by a hydrogen bond

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10
Q

DNA bond

A

phosphodiesterase - 5’ to 3’

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11
Q

Steps of replication of DNA

A

DNA helicase - unwinds ds DNA
DNA polymerase - copies DNA
DNA ligase - winds by the DNA

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12
Q

Types of RNA

A

mRNA - transcription
rRNA - ribosomal
tRNA - transfer - involved in translation

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13
Q

Codons

A
  • made of RNA in triplets
  • each code for only one amino acid
    maximum 64 codons available
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14
Q

Genes are made up of

A

Stretches of nucleotides that code for a polypeptide

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15
Q

Genes have two regions:

A
  1. Exons (coding area)

2. Introns (non-coding area) - mRNA splices out this area during processing

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16
Q

Chromosomes comprised of

A

2 chromatids attached at a centromere

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17
Q

How can you see chromosomes

A

Giemsa Staining at metaphase

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18
Q

Nomenclature of arms

A 
p = short arm
q = long arm
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19
Q

Protein synthesis

A
  1. Transcription :

DNA is transcribed to mRNA by RNA polymerase.
DNA read 3’ to 5’; mRNA is transcribed 5’ to 3’

  1. Translation:

mRNA is translated to amino acids by ribosomes

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20
Q

Polymerase Chain Reaction (PCR)

What is it?
What does it require?

A 
PCR amplifies selected areas in a DNA strand
Needs:
1. 2 primers
2. 4 deoxyxnucleotides
3. Taq polymerase

Is a logarithmic amplification

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21
Q

Types of blotting

A

Southern blotting - DNA
Northern blotting - RNA
Western blotting - protein

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22
Q

Phases of cell cycle

A

Interphase - G1, synthesis and G2

Mitosis - itself made up of four phases

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23
Q

Where does chromosome replication occur?

A

S phase

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24
Q

Proliferation genes

A

c-Myc :

c-Jun :

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25
Q

Inhibiting gene

A

p53

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26
Q

Stem cells - potency

A 
totipotent - can divide in to both embryonic and extra embryonic stem cells
pluripotent
multipotent
oligopotent
unipotent
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27
Q

Mitosis

A

Nuclear division

  • prophase - condensation of chromatins
  • metaphase - mitotic spindles form, align at plate
  • anaphase - chromatids separate
  • telophase - chromosomes decondense, new nuclear membranes

Cytokinesis

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28
Q

Meiosis

A

Production of germ cells - 4 for every 1 parent cell

Meiosis 1 - creates two haploid cells

  • prophase 1
  • metaphase 1
  • anaphase 1
  • telophase 1

Meiosis 2 - similar to mitosis but homologous chromosomes align at the metaphase plate

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29
Q

2 principles of Mendels Law

A

Law of segregation - each gamete only receives 1 allele for each gene
Law of independent assortment - alleles of different genes assort independently of one another during gametogenesis

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30
Q

models of gene inheritance

A

autosomal dominant /recessive
x-linked dominant/recessive
mitochondrial

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31
Q

Types of chromosomal abnormalities

A
  • aneuploidy (change in number of chromosomes)

- structural (translocation, inversion, deletion, duplication, insertion)

32
Q

Down’s syndrome
Genetics
Prevalence

A

Trisomy 21
1:700 live births
Increased nuchal translucency

33
Q

Features of T21

A

Dysmorphic features (small ears, up slanting palpebral fissures, flat facial profile, brachycephaly)

Hypotonia

Cardiac abnormalities

GI tract - duodenal atresia, imperforate anus,
Hirschprungs

Conductive hearing loss

34
Q

T21 have increased risk of:

A

Alzheimer’s
AML/ALL
Hypothyroidism

35
Q

Maternal age risk of T21

A

25: 1:1500
30: 1:900
35: 1:350
40: 1:100
45: 1:30
50: 1:11

Cut off for invasive screening 1:250

36
Q

Edward’s syndrome
Genetics
prevalence

A

T18

1:3000, Male to female 1:2

37
Q

T18 Features

A

Increased nuchal translucency

Musculoskeletal defects:

  • limbs
  • rocker bottom feet
  • overlapping fingers

Facial defects

  • micrognathia
  • cleft lip/palate

Cardiac

  • VSD
  • ASD
  • PDA

Abdominal

  • exomphalos
  • inguinal hernia
  • diaphragmatic hernia
  • renal malformations

IUGR

38
Q

T18 mortality rates

A

by 1 month: 30%
by 2 months: 50%
by 1 year: 90%

39
Q

Patau’s syndrome
Genetics
prevalence

A

T13

1:5000 live births

40
Q

T13 features

A 
Midline defects
- Hypotelorism (close eyes)
- Holoprosencephaly 
- Cleft lip/palate
- Scalp defects
Polydactyly
Congenital heart defects
Renal abnormalities
Omphalocele
IUGR
41
Q

T13 mortality

A

100% by 1 month

42
Q

Sex chromosome aneuploidies

A

Kleinfelter’s 47XXY

Turner’s 45X0

43
Q

Lyon’s hypothesis

A

Explains how females have have XX and the same effect as males X
Barr body - is inactivated condensed X chromosome, present if >2 X chromosomes in the cell
Inactivation of one of the X chromosomes happens at 15-16 days gestation.

44
Q

Turner’s Syndrome
Genetics
Prevalence

A

45X0

1:2500

45
Q

Turner’s Syndrome

Features

A 
Raised nuchal translucency 
Cystic hygroma
Lymphoedema
Neck webbing
Short stature
Wide carrying angle of arms
Shield shaped chest
Coarctation of the aorta
Gonadaldysgenesis
Renal anomalies - eg: horseshoe kidney

Intellectually normal
Risk of gonadoblastoma

46
Q

Kleinfelter’s syndrome
Genetics
Prevalence

A

47XXY

1:1000

47
Q

Kleinfelter’s syndrome

Features

A

Tall
Hypogonadotrophtrophic hypogonadism
Infertility

48
Q

Translocation

A

Exchange of two segments of chromosome between non-homologous chromosomes

  • balanced (even exchange so no chromosomes are gained or lost)
  • unbalanced (missing or extra genes)
49
Q

Deletion - examples

A

DiGeorge’s

Angelman syndrome

Prader-Willi

50
Q

DiGeorge’s

A

DiGeorge’s

  • Immune deficiency
  • Parathyroid dysfunction - hypoCa
  • Autism
  • Congenital heart disease
  • Cleft lip/palate
51
Q

Angelman

A 
Happy disposition
Macroglossia
Ataxia
Seizures
Learning difficulties
52
Q

Prader-Willi

A

Obese
Hypogonadism
Hypotonia

53
Q

Types of genetic disorders

A

Autosomal

  • dominant
  • recessive

X-linked

Mitochondrial

54
Q

Autosomal dominant

A

male : female = equal

Inheritance = 1:2

55
Q

Autosomal recessive

A

Inheritance 1:4 if both parents are carriers

56
Q

X-linked recessive

A 
male = affected
females = carriers
Inheritance =  1:2 sons of carrier females
Inheritance =  all daughters of affected males are carriers
57
Q

X-linked dominant

A

Inheritance = 1:2 offspring of affected females

Severe manifestation in males - miscarriage/IUD of male fetuses

58
Q

Mitochondrial

A

Inherited through the maternal line

Affects both sexes but only passed on maternally

59
Q

Tuberous Sclerosis

Genetics

A

Multisystem - causing tumours to grow in the brain and other vital organs
either TSC1 (chromosome 9, encodes harmatin) or TSC2 (chromosome 16, encodes tuberin)
Harmatin and tuberin are suppressors of tumour growth

60
Q

Tuberous Sclerosis

Clinical features

A

learning difficulties

epilepsy

cardiac rhabdomyomas

renal angiomyolipomas

skin manifestations - angiofibromas, hypomelanotic macule, shagreen patches, ungual fibromas

brain abnormalities - subepydermal nodules, cortical tubers

61
Q

Cystic fibrosis

Genetics

A 
Exocrine secretion
Inc chloride in sweat
1:2000
Carrier rate 1:23
Mutation in CFTR gene (chromosome 7)
Most common is F508
62
Q

Cystic fibrosis

Clinical features

A 
Viscous mucus production 
Recurrent chest infections, poor alveolar gas exchange
Infertility - congenital absence of vas deferent, thickened cervical mucus
Pancreatitis
Cirrhosis
Intestinal obstruction
Malabsorption (ADEK vitamins)
Osteoporosis
Diabetes
63
Q

Sickle cell disease

Genetics

A 
Point mutation in beta chain of Hb - meaning single base change adenine to thymine - causing glutamic acid to valine (aa) (hydrophilic to hydrophobic)
1:500 in London
Homozygous (HbSS)
Heterozygous (HbAS)
Short life span of RBC (10-20/7)
64
Q

Sickle cell disease

Complications

A

Infarction - Hyposplenism, autosplenectomy
Emboli - Stroke, Pul HTN
Ischaemia - Avascular necrosis of the head of the femur, chronic renal failure
Haemolysis - jaundice, cholelithiasis
Infection - osteomyelitis, overwhelming post splenectomy infection
In Preg - IUGR, pre-eclampsia, miscarriage

65
Q

Sickle cell disease

types of crisis

A 
Vado-Occlusive crisis
Acute chest syndrome (fever, pain, SOB)
Aplastic crisis (parvo B19)
Splenic sequestration crisis
Haemolytic crisis
66
Q

Sickle cell disease

Treatment

A

Cyanate - irreversible inhibition of sickling
Hydroxyurea - reactivates fetal Hb
Analgesia
Penicillin
Vaccination for encapsulated organisms (haemophilia influenza, Strep pneumoniae, N meningitides)
Blood transfusion/exchange transfusion
Bone marrow transplant

67
Q

Thalassaemia

Genetics

A

Reduced rate of synthesis of one of the globulin chains - alpha, beta, delta, E thal, S thal, C thal.

Hypochromia - low amount of Hb
Anaemia - excess unpaired chain leads to reduced RBC survival

68
Q

Alpha-thalasseamia

Clinical features

A

1 chain - silent carrier
2 chains - trait - mild hypochromic anaemia
3 chains - Hb H disease, moderate anaemia and splenomegaly
4 chains - Bart’s hydrops - IUD

Tissue hypoxia, Hydrops fettles
Initially fetus OK as using Hb Portland. Distress after 12/40 when using Hb Barts

69
Q

Beta-thalassaemia

Prevalence

A

UK 1:10,000
South Asia 3:100
Cyprus 1:7

70
Q

Beta-thalassaemia

Classifications

A

Major - homologous
Minor/trait - genetically heterozygous
Intermedia - genetically heterozygous

71
Q

Beta-thalassaemia

Clinical features

A

Fatigue
Anaemia
SOB
Jaundice
Skeletal deformities due to increased erythropoiesis
Hepatosplenomegaly due to extramedullary haematopoiesis
Haemochromatosis due to excess iron absorption from the gut
Delayed physical and sexual development secondary to haemochromatosis

72
Q

Beta-thalassaemia major

Treatment

A 
Regular blood transfusion
Folic acid supplementation
Vit D/Ca supplements
Chelation therapy - remove excess iron following transfusions
Splenectomy
Bone marrow transplant
Cord blood transfusion
73
Q

Cystic fibrosis on which chromosome

A

7

74
Q

trisomies and microdeletions

A 
P 13 
A 15
Pr 15
E 18
D  21
Di 22
75
Q

Signs of T21 on quad test

A

reduced AFP - smaller size

bHCG elevated

76
Q

Signs of neural tube defect on quad test

A

high AFP - flows out of neural tube

Normal PAPPA

77
Q

invasive diagnostic testing

A

CVS from 11 weeks

amnio from 15 weeks

MRCOG part 1 (12 decks)

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