JC virus granule cell neuronopathy in a child with CD40 ligand deficiency.

JC virus infection of the brain typically causes progressive multifocal leukoencephalopathy, a demyelinating disease that rarely involves gray matter. This report presents a case of cerebellar degeneration associated with JC virus infection in a male with CD40 ligand deficiency resulting in hyperimmunoglobulin M type 1. This patient exhibited a progressive cerebellar ataxia with progressive atrophy of the cerebellar cortex in association with the presence of JC virus in the spinal fluid. JC virus infection should be considered in the differential diagnosis of ataxia in children with inherited immunodeficiencies.