Unique heterozygous presentation in an infant with DNA ligase IV syndrome

DNA ligase IV deficiency, or ligase 4 (LIG4) syndrome, is a rare autosomal recessive disorder associated with impaired DNA damage-repair mechanisms, resulting in different clinical presentations. The repair of DNA double-stranded breaks through the nonhomologous end-joining pathway is essential in the early stages of B- and T-cell differentiation as they undergo recombination of variable, diverse, and joining gene segments to generate antigen-specific cell receptors.1 Defects in this pathway, as seen in ligase IV deficiency, lead to an extreme form of severe combined immunodeficiency disease with a lymphocyte phenotype described as T-cell negative, B-cell negative, and natural killer cell positive (T−B−NK+).

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