X-linked recessive (↑ in B
oys). Defect in BTK, a tyrosine kinase
gene → blocks pro-B
cells from forming pre-B cells
- Presentation: Recurrent bacterial infection after 6 months
- (↓ maternal IgG) due to opsonization defect.
- -Absence of thymic shadow
: normal pro-B, ↓ maturation, ↓ number of B cells, ↓ immunoglobulins of all classes