Alterations in nuclear factor kappa B (NF-κB) essential modulator (NEMO; HUGO-approved symbol IKBKG) underlie most cases of ectodermal dysplasia with immune deficiency (EDI), a human disorder characterized by anhidrosis with diminished immunity. EDI has also been associated with a single heterozygous mutation at position Ser32 of the NF-κB inhibitor IκBα, one of two phosphorylation sites that are essential for targeting IκBα for proteasomal degradation and hence for activation of NF-κB. We report a novel heterozygous nonsense mutation in theIKBA(HUGO-approved symbol, NFKBIA) gene of a 1-year-old male child with EDI that introduces a premature termination codon at position Glu14. An in-frame methionine downstream of the nonsense mutation allows for reinitiation of translation. The resulting N-terminally truncated protein lacks both serine phosphorylation sites and inhibits NF-κB signaling by functioning as a dominant negative on NF-κB activity in lymphocytes and monocytes. These findings support the scanning model for translation initiation in eukaryotes and confirm the critical role of the NF-κB in the human immune response. Hum Mutat 29(6), 861-868, 2008.