To the Editor.
—The vast majority of genetically defined primary immunodeficiency diseases are typically considered within the context of the pediatric population.1 Genetic confirmation of primary immunodeficiency diseases in patients with atypical clinical features and often uninformative family histories has emphasized the wide phenotypic variation associated with these disorders.2 The Bruton tyrosine kinase (Btk) gene, which is mutated in X-linked agammaglobulinemia (XLA), represents the most extensively studied example of genetic mutation in a primary immunodeficiency disease1: at least 228 unique mutation events are known to be associated with XLA.3 Less than 25% of known mutations have been identified in 2 or more unrelated individuals,3 suggesting the possibility of additional mutant genotypes (and phenotypes). The phenotypic presentation of XLA is varied in terms of numbers of B cells, immunoglobulin levels, and clinical presentation.We have recently identified a novel mutation, which introduces a premature termination codon in Btk
Kornfeld SJ, Haire RN, Litman GW. Primary Immunodeficiency Disease Presenting in Midlife. JAMA. 1996;276(24):1953–1954. doi:10.1001/jama.1996.03540240031021
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