IKBKG (nuclear factor-kappa B essential modulator) mutation can be associated with opportunistic infection without impairing Toll-like receptor function.

ABSTRACT

BACKGROUND: Patients with hypomorphic nuclear factor-kappaB essential modulator (NEMO) mutations have extensive phenotypic variability that can include atypical infectious susceptibility. OBJECTIVE: This study may provide important insight into immunologic mechanisms of host defense. METHODS: Immunologic evaluation, including studies of Toll-like receptor (TLR) function, was performed in a 6-month-old boy with normal ectodermal development who was diagnosed with Pneumocystis pneumonia and cytomegalovirus sepsis. RESULTS: Genomic and cDNA sequencing demonstrated a novel NEMO missense mutation, 337G->A, predicted to cause a D113N (aspartic acid to asparagine) substitution in the first coiled-coil region of the NEMO protein. Quantitative serum immunoglobulins, lymphocyte subset numbers, and mitogen-induced lymphocyte proliferation were essentially normal. The PBMC responses to TLR ligands were also surprisingly normal, whereas natural killer cell cytolytic activity, T-cell proliferative responses to specific antigens, and T-cell receptor-induced NF-kappaB activation were diminished. CONCLUSION: Unlike the unique NEMO mutation described here, the most commonly reported mutations are clustered at the 3' end in the tenth exon, which encodes a zinc finger domain. Because specific hypomorphic variants of NEMO are associated with distinctive phenotypes, this particular NEMO mutation highlights a dispensability of the region including amino acid 113 for TLR signaling and ectodysplasin A receptor function. This region is required for certain immunoreceptor functions as demonstrated by his susceptibility to infections as well as natural killer cell and T-cell defects.