Class switch recombination defect in child with ataxia-telangiectasia with hyper IgM phenotype

Abstract

Ataxia-telangiectasia (AT) is a rare autosomal recessive disease characterized by cerebellar ataxia, ocular and/or cutaneous telangiectasia, immune deficiency, enhanced radiosensitivity, and susceptibility to malignancy. It is caused by mutations in the AT mutated ( ATM ) gene. Hyper-IgM phenotypes are characterized by a class-switch recombination defect, IgG and IgA deficiencies, immune dysregulation, and lymphoproliferative disorders. In this case report, a 6.5-year-old Egyptian A-T female had progressive hepatosplenomegaly, hypersplenism, generalized lymphadenopathy, and high levels of IgM. This patient had a class switch recombination defect (CSRD), leading to the diagnosis of HIgM-phenotype of ataxia-telangiectasia with class switch defect (HIgM AT-CSD). In reporting this case, we hope to highlight its rarity and complexity in a pediatric patient with AT, as well as the potential role of an appropriate diagnostic assessment in achieving successful clinical outcomes. The presence of hepatosplenomegaly and lymphadenopathy in AT suggests malignancy or infection, but after exclusion of these causes, pediatricians must consider HIgM AT-CSD as a possible cause of lymphoproliferation.