Immune deficiencies, infection, and systemic immune disorders IKBKG (nuclear factor-kB essential modulator) mutation can be associated with opportunistic infection without impairing Toll-like receptor function Bryn H. Salt, MD, a Julie E. Niemela, BS, b Rahul Pandey, PhD, c Eric P. Hanson, MD, c Raquel P. Deering, BA, c Ralph Quinones, MD, d Ashish Jain, MD, b Jordan S. Orange, MD, PhD, c * and Erwin W. Gelfand, MD a * Denver, Colo, Bethesda, Md, and Philadelphia, Pa Background: Patients with hypomorphic nuclear factor-kB 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-kB activation were diminished. Conclusion: Unlike the unique NEMO mutation described here, the most commonly reported mutations are clustered at the 39 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. (J Allergy Clin Immunol 2008;121:976-82.) Key words: NEMO, Toll-like receptors Mutations in the nuclear factor-kB essential modulator (NEMO) gene (also referred to as IKBKG) on the X chromosome have been associated with anhidrotic ectodermal dysplasia as well as immunodeficiency in male subjects. 1 Complete deficiency of NEMO activity is incompatible with male survival, because at least some NEMO function is required for fetal development. Women who possess 1 completely nonfunctional copy of NEMO have incontinentia pigmenti characterized by dermal scarring and abnormal pigmentation. 2 As a result, the NEMO mutants compat- ible with male survival are hypomorphic and still allow some crit- ical NEMO functions to occur, whereas others fail. The majority of male patients with NEMO hypomorphisms reported to date have alterations affecting the c-terminus of the protein containing a zinc-finger domain. 3 These patients typically have ectodermal dysplasia and immunodeficiency characterized by impaired B-cell function and susceptibility to severe infections. 4 Some patients with mutations affecting other regions of NEMO have distinct pheno- types, including normal ectodermal development, 5 lymphedema, and osteopetrosis 6 as well as less severe impairment of B-cell function. 5 One defect that has been relatively pervasive in male patients with NEMO hypomorphisms described thus far has been an impairment of Toll-like receptor (TLR) function, 7 accounting for their susceptibility to mycobacteria and other pathogens. Nuclear factor-kB essential modulator is a scaffold protein of 519 amino acids and is an integral part of the inhibitor of nuclear factor-kB (IkB) kinase (IKK) complex. NEMO and the IKK are critical links in facilitating the nuclear translocation of nuclear factor-kB (NF-kB) transcription factors. The classic IKK com- plex consists of NEMO and at least 2 kinase subunits, IKK-a and IKK-b. When assembled and activated after the ligation of a relevant receptor, IKK can target IkB in the cell cytoplasm to affect its phosphorylation, ubiquitination, and degradation. Because IkB is bound to NF-kB and prevents it from translocating into the nucleus, the degradation of IkB frees NF-kB to move into the nucleus and subsequently promote gene transcription. NF-kB is required for the signal transduction of a number of surface and cytoplasmic receptors including T-cell receptors (TCRs), B-cell receptors, IL-1 receptor and TNF receptor superfamilies, and the TLRs. NEMO is therefore an essential regulator of NF-kB From a the Department of Pediatrics, National Jewish Medical and Research Center, Den- ver; b the National Institutes of Health, Bethesda; c the Children’s Hospital of Philadel- phia, Joseph Stokes Jr. Research Institute; and d Children’s Hospital, Denver. *These authors contributed equally to this work. Supported in part by grants from the US Immunodeficiency Network and Philadelphia Department of Health (J.S.O.), and by the Jeffrey Model Diagnostic Center at the Chil- dren’s Hospital of Philadelphia. Disclosure of potential conflict of interest: The authors have declared that they have no conflict of interest. Received for publication August 2, 2007; revised November 5, 2007; accepted for publication November 7, 2007. Available online January 21, 2008. Reprint requests: Jordan S. Orange, MD, PhD, Children’s Hospital of Philadelphia, 3615 Civic Center Blvd, ARC 1016H, Philadelphia, PA 19104. E-mail: orange@mail.med. upenn.edu; Erwin W. Gelfand, MD, Division of Cell Biology, Department of Pediatrics, National Jewish Medical and Research Center, Denver, CO 80206. E-mail: gelfande@njc.org. 0091-6749 doi:10.1016/j.jaci.2007.11.014 976