NEED TO UPDATE THE WHO DIAGNOSTIC CRITERIA FOR XLA BRUTON DISEASE.

N. Pozzi. L. Gaetaniello, E. Anastasio, P. Orlandi^°, V. Moschese^°, M.R. D'Armiento*, L. Maiuri and C. Pignata.

Department of Pediatrics, Unit of Immunology, *Pathology, "Federico II" University, Naples, and °Bambino Gesù, "Tor Vergata" University, Rome. Italy.

OBJECTIVE: The WHO (World Health Organization) diagnostic criteria for X-linked agammaglobulinemia (XLA), former known as Bruton disease, include the absence of immunoglobulin production and lack of circulating mature B cells. This inherited disease is caused by mutations of the Bruton tyrosine kinase (Btk), which plays an essential role in the B-cell development. We report on 2 unrelated pts (11 y and 12 y, male) affected by an atypical agammaglobulinemia characterized by lack of mature B cells, but with normal serum IgG levels.

METHODS: The immunological assessment was performed by evaluation of the proliferative response to common mitogens and 3-H thymidine incorporation; surface markers were detected by flow cytometry, B cells detection on bioptic tissue was performed by using standard immunoflurescence and immunohistochemical procedures. Btk gene analysis was performed by using the screening mutations assay NIRCA (Non Isotopic RNAse Cleavage Assay).

RESULTS: Immunophenotype analysis revealed absent CD19+ (0.9 and 0.6%), normally differentiated T and NK cells, normal expression of HLA-DR in both pts. The proliferative response following stimulation with PHA, PMA+ionomycin, Con-A, and cross-linking of CDS was normal in both pts. Laboratory evaluation, obtained at the time of diagnosis prior to IV-Ig therapy, revealed normal IgG levels (591 and 579 mg/dl), while IgA and IgM were markedly reduced in both pts. Moreover, B cells were unable to produce isohemagglutinins and specific antitetanus toxoid Ab. In pt1, a biopsy of a stimulated lymph node (not performed in pt2) revealed the absence of B-dependent areas, and no B cells were detected. On the contrary, the intestinal biopsy showed the presence of a normal follicle in pt1, indicating the presence of B lymphocytes, and the presence of scarce, but present, mature type B cells (CD19+, IgG+ and IgA+ plasma cells) in both pts with very low expression of secretory IgA in the crypt enterocytes. Btk gene analysis failed to identify mutations in pt1 whereas in pt2 a single nucleotide change A²⁴⁹ C resulting in an aminoacid substitution of Tyr Ser (Y39) in the PH domain was identified.

CONCLUSIONS: Our data suggest that XLA is an example of a complex monogenic disease, whose clinical phenotype may be modified by interfering factors. In our pts, the presence of serum IgG in spite of the absence of mature type circulating B cells, indicate that WHO diagnostic criteria for XLA need to be updated.