Genetics

Question 1

What are some of the characteristics of trisomy 21? What is the primary cause?

Answer 1

DOWN SYNDROME

• mental retardation
• epicanthic folds
• simian
• congenital heart defects
• umbilical hernia
• leukaemia
• dementia
• maternal non-disjunction 21%
• other causes: paternal non-disjunction, translocation, mosaicism

Question 2

What is the other name for trisomy 18 and what are some of the key characteristics?

Answer 2

Edwards Syndrome

Question 3

What is the other name for trisomy 13 and what are some of the key characteristics?

Answer 3

Patau Syndrome

Question 4

What is the characteristic haplotype of Turner’s syndrome and some of the phenotypic features?

Answer 4

(45,X)

Growth retardation
Neck webbing
Cubitus valgus (increased carrying angle of the arms)
Shield-like chest with widely spaced nipples
High-arched palate
Lymphoedema of the hands and feet
Congenital malformations eg. horseshoe kidney, bicuspid aortic valve, coarctation of the aorta
Primary hypogonadism

Normal mental status

Question 5

What sort of genetic mutations underly the pathophysiology of Angelman and Prader-Willi syndromes?

Answer 5

Genomic imprinting

• Maternal imprinting = silencing of the maternal allele - Angelman
• Paternal imprinting = inactivating paternal allele - Prader-Willi

Question 6

What is the characteristic haplotype of Klinefelter’s syndrome and some of the phenotypic features?

Answer 6

(47,XXY)
- extra X chromosomes, usually from non-disjunction

o elongated body
o Eunuchoid body habitus
o Reduced facial, body and pubic hair
o Gynaecomastia
o Hypogonadism – small testes, lower testersterone levels
o Mental retardation (mild)
o Increased risk of breast Ca compared to males; ↑risk of germ cell tumours and autoimmune diseases

Question 7

What is the inheritance pattern of familial adenomatous polyposis? What gene is responsible?

Answer 7

autosomal dominant; APC gene on chromosome 5q21

Question 8

What is the patten of inheritance of familial hypercholesterolaemia? What is the gene affected and the pathophysiology?

Answer 8

Autosomal dominant

mutation in low density lipoprotein (LDL) receptor gene on chromosome 19. loss of feedback inhibition of HMG Co-A reductase and increased levels of circulating cholesterol