X-linked (Bruton's) agammaglobulinemia (XLA) is a primary immunodeficiency caused by a block in B-cell development caused by mutations in the Bruton's tyrosine kinase (BTK) gene.

A retrospective clinical and immunological survey in 6 male children  clinically diagnosed as XLA on the basis of hypo- or agammaglobulinemia . Molecular diagnosis is done in referent center in 4  patients. The results of mutation analysis of the BTK gene performed at the DNA level are following: 1) two brothers : Tryptophan mutations 634 Stop – Guanine 2033 Adenine with polymorphism in exon 18 Cysteine 633 Cysteine – Thymine 2031 Cytosine 2) one case: insertion of a cytosine in a stretch of cytosines, 3) one case: Aspartic acid 579 Asparagines mutation. Patients' ages is from 5 to 23 years.  Mean age at diagnosis and mean duration of follow-up were 3.5 and 7,5 years respectively. 2 are sporadic and 2 familial cases. Respiratory infections were the most frequent manifestation both prior to diagnosis and over follow-up ( otitis, chronic sinusitis, bronchopneumonia ).  Patients were evaluated by respiratory function tests and computed tomography and  2 had chronic lung disease. Other infections developed, including enteral infections with Giardia- Lamblia (3) and aseptic arthritis (2). In 4 patients puberty was normal. Since 1996 all were on intravenous immunoglobulin (IVIg) substitution therapy  (0.40 g/kg every 3 weeks), mean individual residual IgG levels ranged  500 - 1140 mg/dL (median, 700 mg/dL. During IVIg replacement, the incidence of bacterial infections requiring hospitalization fell.