Identification of deletions in the btk gene allows unambiguous assessment of carrier status in families with X-linked agammaglobulinaemia.

Mutations within the btk gene have recently been shown to cause X-linked agammaglobulinaemia (XLA). Altered patterns of DNA restriction fragments are seen by Southern blot analysis of DNA from affected patients with deletions in the btk gene. We have identified seven affected families in which altered restriction fragments can be used to diagnose and confirm the carrier status of female relatives of affected boys and in prenatal diagnosis.