Hyper-IgM syndrome: report of one case.

The hyper-IgM syndrome (HIM) is a rare primary immunodeficiency disorder caused by defects in the CD40 ligand (CD40L)/CD40-signaling pathway. It is characterized by recurrent infections with markedly decreased IgG, IgA and IgE levels but normal or elevated serum IgM levels. A 5-month-old boy presented with rapidly progressive pneumonia which responded poorly to antibiotics. High levels of IgM and very low levels of IgG, IgE and IgA were noted in his plasma specimen (IgM, 128 mg/dl; IgG, 18 mg/dl; IgE, 1 IU/ml; IgA, 4 mg/dl). The relative proportions of immune cells were CD3 24.6%, CD4 10.3%, CD8 2.2%, CD19 30.2%, CD57 1.0% and active T cells 1.1%. After IVIG treatment, the pneumonia improved. Repeat assessment at the age of 15 months showed IgM decreased to the normal range (32 mg/dl). Whole blood flow cytometry assay for CD40L expression confirmed the diagnosis of hyper-lgM syndrome when he was 21 months old. Only a small percentage (0.48%) of the patient's in vitro activated CD4+ T cells expressed CD40L, compared with 33.54% from a healthy control. The patient's father, mother and sister all had a normal CD40L expression activation patterns (43.52%, 40.78%, 34.11%, respectively). On a regimen of monthly IVIG infusion and oral trimethoprim-sulfamethoxazole for Pneumocystis carinii pneumonia (PCP) prophylaxis, the patient has had no recurrent infections.