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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
Inhibiting gene
p53
26
Stem cells - potency
``` totipotent - can divide in to both embryonic and extra embryonic stem cells pluripotent multipotent oligopotent unipotent ```
27
Mitosis
Nuclear division - prophase - condensation of chromatins - metaphase - mitotic spindles form, align at plate - anaphase - chromatids separate - telophase - chromosomes decondense, new nuclear membranes Cytokinesis
28
Meiosis
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
29
2 principles of Mendels Law
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
30
models of gene inheritance
autosomal dominant /recessive x-linked dominant/recessive mitochondrial
31
Types of chromosomal abnormalities
- aneuploidy (change in number of chromosomes) | - structural (translocation, inversion, deletion, duplication, insertion)
32
Down's syndrome Genetics Prevalence
Trisomy 21 1:700 live births Increased nuchal translucency
33
Features of T21
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
T21 have increased risk of:
Alzheimer's AML/ALL Hypothyroidism
35
Maternal age risk of T21
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
Edward's syndrome Genetics prevalence
T18 | 1:3000, Male to female 1:2
37
T18 Features
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
T18 mortality rates
by 1 month: 30% by 2 months: 50% by 1 year: 90%
39
Patau's syndrome Genetics prevalence
T13 | 1:5000 live births
40
T13 features
``` Midline defects - Hypotelorism (close eyes) - Holoprosencephaly - Cleft lip/palate - Scalp defects Polydactyly Congenital heart defects Renal abnormalities Omphalocele IUGR ```
41
T13 mortality
100% by 1 month
42
Sex chromosome aneuploidies
Kleinfelter's 47XXY | Turner's 45X0
43
Lyon's hypothesis
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
Turner's Syndrome Genetics Prevalence
45X0 | 1:2500
45
Turner's Syndrome | Features
``` 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
Kleinfelter's syndrome Genetics Prevalence
47XXY | 1:1000
47
Kleinfelter's syndrome | Features
Tall Hypogonadotrophtrophic hypogonadism Infertility
48
Translocation
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
Deletion - examples
DiGeorge's Angelman syndrome Prader-Willi
50
DiGeorge's
DiGeorge's - Immune deficiency - Parathyroid dysfunction - hypoCa - Autism - Congenital heart disease - Cleft lip/palate
51
Angelman
``` Happy disposition Macroglossia Ataxia Seizures Learning difficulties ```
52
Prader-Willi
Obese Hypogonadism Hypotonia
53
Types of genetic disorders
Autosomal - dominant - recessive X-linked Mitochondrial
54
Autosomal dominant
male : female = equal | Inheritance = 1:2
55
Autosomal recessive
Inheritance 1:4 if both parents are carriers
56
X-linked recessive
``` male = affected females = carriers Inheritance = 1:2 sons of carrier females Inheritance = all daughters of affected males are carriers ```
57
X-linked dominant
Inheritance = 1:2 offspring of affected females | Severe manifestation in males - miscarriage/IUD of male fetuses
58
Mitochondrial
Inherited through the maternal line | Affects both sexes but only passed on maternally
59
Tuberous Sclerosis | Genetics
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
Tuberous Sclerosis | Clinical features
learning difficulties epilepsy cardiac rhabdomyomas renal angiomyolipomas skin manifestations - angiofibromas, hypomelanotic macule, shagreen patches, ungual fibromas brain abnormalities - subepydermal nodules, cortical tubers
61
Cystic fibrosis | Genetics
``` Exocrine secretion Inc chloride in sweat 1:2000 Carrier rate 1:23 Mutation in CFTR gene (chromosome 7) Most common is F508 ```
62
Cystic fibrosis | Clinical features
``` 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
Sickle cell disease | Genetics
``` 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
Sickle cell disease | Complications
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
Sickle cell disease | types of crisis
``` Vado-Occlusive crisis Acute chest syndrome (fever, pain, SOB) Aplastic crisis (parvo B19) Splenic sequestration crisis Haemolytic crisis ```
66
Sickle cell disease | Treatment
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
Thalassaemia | Genetics
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
Alpha-thalasseamia | Clinical features
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
Beta-thalassaemia | Prevalence
UK 1:10,000 South Asia 3:100 Cyprus 1:7
70
Beta-thalassaemia | Classifications
Major - homologous Minor/trait - genetically heterozygous Intermedia - genetically heterozygous
71
Beta-thalassaemia | Clinical features
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
Beta-thalassaemia major | Treatment
``` 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
Cystic fibrosis on which chromosome
7
74
trisomies and microdeletions
``` P 13 A 15 Pr 15 E 18 D 21 Di 22 ```
75
Signs of T21 on quad test
reduced AFP - smaller size | bHCG elevated
76
Signs of neural tube defect on quad test
high AFP - flows out of neural tube | Normal PAPPA
77
invasive diagnostic testing
CVS from 11 weeks | amnio from 15 weeks

MRCOG part 1 (12 decks)

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