X-Linked Dominant Disorders

Question 1

Denoted:

Answer 1

XAXa = affected
XAXA/XAY = affected
XaXa/XaY = normal

Question 2

Vitamin D-Resistant Rickets (familial hypophosphatemia)

Answer 2

Defect in renal tubular reabsorption of PO4, leads to hypophosphatemia

Cause: PHEX gene = PHEX protein, which usually helps absorb PO4 in renal tubules

Question 3

Rett Syndrome

Answer 3

Lethal in Males
Exclusively in females as living examples

Males who do survive usually have 2 X chromosomes = XXY (Klinefelter Syndrome)

Mutation in MECP2 gene