Carrier detection and prenatal diagnosis of X-linked agammaglobulinemia.

We investigated the pregnant mother of a boy with X-linked agammaglobulinemia (XLA) but with no family history of immune disease. The X-inactivation pattern was found, using a methylation-sensitive probe, to be skewed in the maternal B cells but random in the polymorphonuclear cells, indicating carrier status and a 50% risk of inheritance for her male fetus. Using probes assigned to regions on either side of the XLA locus and defining RFL polymorphism, we excluded for the first time a diagnosis of XLA on a chorionic villus sample, with a risk of error less than 0.003. Immunological studies performed at the 19th week of gestation and 3 days after birth confirmed normality. Carrier detection based on the X-chromosome inactivation pattern, together with prenatal studies using probes close to the disease locus, thus permits prenatal diagnosis in families with isolated cases of XLA.