Genetics Flashcards by Hayley White

Lifetime risk of breast/ ovarian cancer with BRCA1 vs BRCA 2 gene

Breast: BRCA 1 50-65%, BRCA 2 40-55%

Ovarian: BRCA 1 40-65%, BRCA 2 15-25%

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Human placental lactogen (HPL) structure

Polypeptide, 191 AAs. Similar to human growth hormone

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Klinefelter’s syndrome

47 XXY
1:1000 live births
Features: tall, small testes with hypogonadotrophic hypogonadism, infertility

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Types of blotting and what they detect

Northern- RNA
Southern- DNA sequence
Western- Protein

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Mode of inheritance of BRCA genes

Autosomal dominant

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Prevalence of Turner’s syndrome (45XO)

1 in 2500 live female births

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Cell cycle stages and what happens in each

G1 (1st gap) –> S (Synthesis) –> G2 (2nd gap) –> M (mitosis) –> G1 (1st gap)

G1: Cell increases in size
S: Duplication of DNA
G2: Prepares for cell division
M: Mitosis

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Introns vs exons

Exons = coding areas: code for protein that the gene encodes. Sequence is highly conserved between individuals

Introns = non-coding areas (longer than exons, not well conserved between individuals, spliced out during processing to mRNA)

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DNA replication is…

Semi-conservative (every double helix in the new generation of an organism consists of one complete ‘old’ strand and one complete ‘new strand’

Bi-directional (one strand is 5’ to 3’ and the other is 3’ to 5’)

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Base pairs DNA/ RNA

Pyrimidine-Purine

DNA:
Cytosine-Guanine
Adenosine-Thymine

RNA:
Cytosine-Guanine
Adenosine-Uracil

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Karyotype of Turner syndrome

45XO

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Lifetime risk of breast/ ovarian ca in general female population

Breast: 12%

Ovarian: 1.3%

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Typical blood results for Down’s syndrome

Low PAPP-A
Low AFP
Low uE3
Elevated inhibin and beta hCG

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Typical blood results for Edwards

Low PAPP-A
Low AFP
Low uE3
Low inhibin A
Low beta hCG

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Combined test: what does it include and what is the wind to do it in?

PAPP-A, hCG and USS

11+2 to 14+1
NICE: 11+0 and 13+6

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Triple test: what does it include?

AFP, hCG and uE3

Quadruple test: what does it include and what is the wind to do it in?

AFP, hCG, inhibit A and uE3

14+2 to 20+0

When should the mid-trimester anomaly scan take place?

18+0 to 20+6

What percentage of inherited breast cancers are caused by BRCA gene mutations?

25%

What percentage of people diagnosed with breast cancer will have a BRCA gene mutation?

Men with BRCA mutation are at increased risk of breast ca- what is their lifetime risk?

1-7%

HNPCC: lifetime risk of colorectal and endometrial cancer

Colorectal: 78%
Endometrial 43%

What percentage of Turner syndrome conceptions will miscarry?

95-99%

Features of Turner syndrome

Clinically short stature, obesity, webbed neck, murmurs, ovarian failure (primary amenorrhoea), failure to develop secondary sexual characteristics

Raised FSH and LH (after age 10)

Thyroid dysfunction is common

What are low vs high levels of AFP associated with in pregnancy

High: neural tube defects, anencephaly, multiple pregnancy, oesophageal and abdominal defects Low: Down's and Edward's

Inheritance pattern of beta thalassemia

Autosomal recessive Homozygous b-thalassaemia (Major) produces severe transfusion dependent anaemia Heterozygote b-thalassaemia produces mild microcytic anaemia

Incidence of thalassaemia

1 in 100000 global incidence/ 70,000 babies born each year

Gene mutation for beta thalassaemia

HBB gene chromosome 11

Management of beta thalassaemia in pregnancy

- Screen for diabetes - TFT screen - ECG and T2 cardiac MRI & cardiology review at 28 weeks - Biliary USS and ferriscan or liver T2 - Offer bone density scan - Folic acid 5mg 3 months prior to conception - Major: should receive blood transfusions on a regular basis aiming for Hb >100 - Offer early scan at 7-9 weeks - Serial growth scans 4 weekly from 24 weeks

Thromboprophylaxis in pregnancy & beta thalassaemia

Women with thalassaemia who have undergone splenectomy and have a platelet count >600 should be offered LMWH & Aspirin (75 mg/day) Women with thalassaemia who have undergone splenectomy or have a platelet count >600 should be commenced on Aspirin (75 mg/day) Women with thalassaemia who are not already using prophylactic low-molecular-weight heparin should be advised to use it during antenatal hospital admissions

What genetic mutation is Cri-du-Chat caused by?

Micro deletion of chromosome 5

What are 90% of congenital adrenal hyperplasia cases caused by?

Abnormal CYP21A genes leading to 21 hydroxylase deficiency, resulting in androgen excess and mineralocorticoid deficiency 5% are due to 11 hydroxylase deficiency

What is the leading cause of Down's syndrome?

Nondisjunction maternal gamete

What is the detection rate of Down syndrome using NT alone?

70%

What percentage of miscarriages are thought to be attributed to Turner syndrome?

10-15%

What percentage of first trimester miscarriages are due to trisomies?

68%

HNPCC inheritance pattern

Autosomal dominant

Kallman syndrome Genetic inheritance/ gene mutation

A form of hypogonadotropic hypogonadism resulting from a lack of production of FSH and LH Also experience lack of sense of smell X linked recessive inheritance (no reported cases in females) ANOS1 gene mutation

Hb present in beta thalassaemia minor/ major

Minor: HbA (92-5%), Hb A2 (3-7%), HbF (1-5%) Major: Higher percentages of HbF and HbA2 with absent or very low HbA