Severe combined immunodeficiency caused by a new homozygous RAG1 mutation with progressive encephalopathy

We describe an unusual case of severe combined immunodeficiency (SCID) with neutropenia and central nervous system (CNS) manifestations in which a novel RAG1 mutation was identified. A 15-month-old boy presented with failure to thrive, neutropenia and recurrent infections. He was diagnosed with T-B-NK+ SCID. He subsequently developed right partial seizures with ipsilateral hemiparesis and became comatose. Magnetic resonance imaging (MRI) of the brain revealed an inflammatory lesion in the left thalamus which later progressed to diffuse meningo-encephalitis on serial imaging. No CNS infection was documented. Genetic work-up in the child revealed a novel homozygous deleterious mutation in the RAG1 gene (c:2881T>C; p:I794T), for which both parents were heterozygous. He underwent a haploidentical bone marrow transplant without conditioning and died on day +35 with no improvement in his neurological status. The features of neutropenia and progressive encephalopathy could be linked to the novel genetic defect but more data is required to establish this conclusively.