RESUMEN
X-linked hyperimmunoglobulin M (HIGM) syndrome may increase the susceptibility of patients to disseminated cryptococcal infections primarily due to CD40L deficiency that causes defective cross talk between T- and B-cells, thus preventing class switching. In HIGM syndrome, serum IgM levels are elevated with severe reduction in serum immunoglobulin G (IgG) and IgA levels. In addition, the expression of CD40L (CD154) on in vitro-activated T-cells is severely reduced or absent. Here, we describe a rare, and perhaps, the first reported case in India of a 3-year-old male child with X-linked HIGM immunodeficiency syndrome who developed disseminated Cryptococcosis. Evaluation of the serum IgG profile of the patient revealed increased serum IgM levels with reduced IgG and IgA levels. Both the frequency and the function of T-cells, primarily CD40L on activated T-cells, showed weak expression suggestive of HIGM syndrome.