Abstract
BACKGROUND: Human hypomorphic nuclear factor-kappaB essential modulator (NEMO) mutations cause diverse clinical and immunologic phenotypes, but understanding of their scope and mechanistic links to immune function and genotype is incomplete. OBJECTIVE: We created and analyzed a database of hypomorphic NEMO mutations to determine the spectrum of phenotypes and their associated genotypes and sought to establish a standardized NEMO reconstitution system to obtain mechanistic insights. METHODS: Phenotypes of 72 individuals with NEMO mutations were compiled. NEMO L153R and C417R were investigated further in a reconstitution system. TNF-alpha or Toll-like receptor (TLR)-5 signals were evaluated for nuclear factor-kappaB activation, programmed cell death, and A20 gene expression. RESULTS: Thirty-two different mutations were identified; 53% affect the zinc finger domain. Seventy-seven percent were associated with ectodermal dysplasia, 86% with serious pyogenic infection, 39% with mycobacterial infection, 19% with serious viral infection, and 23% with inflammatory diseases. Thirty-six percent of individuals died at a mean age of 6.4 years. CD40, IL-1, TNF-alpha, TLR, and T-cell receptor signals were impaired in 15 of 16 (94%), 6 of 7 (86%), 9 of 11 (82%), 9 of 14 (64%), and 7 of 18 (39%), respectively. Hypomorphism-reconstituted NEMO-deficient cells demonstrated partial restoration of NEMO functions. Although both L153R and C417R impaired TLR and TNF-alpha-induced NF-kappaB activation, L153R also increased TNF-alpha-induced programmed cell death with decreased A20 expression. CONCLUSION: Distinct NEMO hypomorphs define specific disease and genetic characteristics. A reconstitution system can identify attributes of hypomorphisms independent of an individual's genetic background. Apoptosis susceptibility in L153R reconstituted cells defines a specific phenotype of this mutation that likely contributes to the excessive inflammation with which it is clinically associated.