A 4 year old boy presents with worsening unsteadiness while walking and slurring of speech for a few months. His medical history is significant for recurrent respiratory tract infections for several years. His sister died of overwhelming sepsis at 13 years, following a similar illness with recurrent respiratory infections and developmental regression. His parents are apparently normal. His birth history is unremarkable and all immunizations are up to date.
The MRI of the brain shows cerebellar atrophy with widened cerebellar sulci and enlargement of the fourth ventricle. No structural brain lesions are noted.
The thymic shadow is absent. No other abnormalities are noted.
IgM: 60 mg/dl (normal) IgG: 910 mg/dl (normal) IgA: 3 mg/dl (< 2 SD below normal)
AFP levels are 17.8 ng/ml (normal: < 5mg/ml)