X linked dominant and recessive

Question 1

give examples of conditions which have X-LINKED DOMINANT inheritance

Answer 1

Alport’s syndrome
Rett syndrome
Vitamin D resistant rickets

Question 2

In X linked recessive disorders, which gender is typically affected?

Answer 2

only males are affected

exception: Turner’s syndrome (having one X chromosome)

Question 3

How are X-linked conditions transmitted?

Answer 3

transmitted by heterozygote females (carriers)

Affected males can only have unaffected sons and carrier daughters.

Question 4

If a mother is a carrier of an X-linked recessive condition, what are the chances her son will be affected? What are the chances her daughter will be a carrier?

Answer 4

50% chance her son will be affected
50% chance daughter will be a carrier

Question 5

If a female is homozygous for an X-Linked recessive condition (RARE), will she show clinical signs?

Answer 5

They do have some clinical manifestations of the disorder

E.g. in certain Afro-Caribbean communities G6PD deficiency is relatively common and homozygous females with clinical manifestations of the enzyme defect are seen.

Question 6

Give examples of X-Linked recessive conditions

Answer 6

Androgen insensitivity syndrome
Becker muscular dystrophy
Colour blindness
Duchenne muscular dystrophy
Fabry’s disease
G6PD deficiency
Haemophilia A,B
Hunter’s disease
Lesch-Nyhan syndrome
Nephrogenic diabetes insipidus
Ocular albinism
Retinitis pigmentosa
Wiskott-Aldrich syndrome