A novel ATM mutation associated with elevated atypical lymphocyte populations, hyper-IgM, and cutaneous granulomas

Ataxia-Telangiectasia (AT) is an immunodeficiency most often associated with T cell abnormalities. We describe a patient with a hyper-IgM phenotype and immune cell abnormalities that suggest a distinct clinical phenotype. Significant B cell abnormalities with increased unswitched memory B cells, decreased naive transitional B cells, and an elevated frequency of CD19⁺CD38^loCD27^-CD10^-CD21^-/low B cells expressing high levels of T-bet and Fas were demonstrated. The B cells were hyporesponsive to in vitro stimulation through the B cell receptor, Toll like receptors (TLR) 7 and 9, and CD40. T cell homeostasis was also disturbed with a significant increase in γδ T cells, circulating T follicular helper cells (Tfh), and decreased numbers of T regulatory cells. The ATM mutations in this patient are posited to have resulted in the perturbations in the frequencies and distributions of B and T cell subsets, resulting in the phenotype in this patient. KEY MESSAGES: A novel mutation creating a premature stop codon and a nonsense mutation in the ATM gene are postulated to have resulted in the unique clinical picture characterized by abnormal B and T cell populations, lymphocyte subset dysfunction, granuloma formation, and a hyper-IgM phenotype. CAPSULE SUMMARY: A patient presented with ataxia-telangiectasia, cutaneous granulomas, and a hyper-IgM phenotype; a novel combination of mutations in the ATM gene was associated with abnormal distributions, frequencies, and function of T and B lymphocyte subsets.