REPORT Whole-Exome-Sequencing-Based Discovery of Human FADD Deficiency Alexandre Bolze, 1 Minji Byun, 1,13 David McDonald, 2,13 Neil V. Morgan, 3,13 Avinash Abhyankar, 1,13 Lakshmanane Premkumar, 4,13 Anne Puel, 5 Chris M. Bacon, 6 Fre ´de ´ric Rieux-Laucat, 7 Ki Pang, 8 Alison Britland, 9 Laurent Abel, 1,5 Andrew Cant, 2,10 Eamonn R. Maher, 3,11 Stefan J. Riedl, 4 Sophie Hambleton, 2,10 and Jean-Laurent Casanova 1,5,12, * Germline mutations in FASL and FAS impair Fas-dependent apoptosis and cause recessively or dominantly inherited autoimmune lym- phoproliferative syndrome (ALPS). Patients with ALPS typically present with no other clinical phenotype. We investigated a large, consanguineous, multiplex kindred in which biological features of ALPS were found in the context of severe bacterial and viral disease, recurrent hepatopathy and encephalopathy, and cardiac malformations. By a combination of genome-wide linkage and whole-exome sequencing, we identified a homozygous missense mutation in FADD, encoding the Fas-associated death domain protein (FADD), in the patients. This FADD mutation decreases steady-state protein levels and impairs Fas-dependent apoptosis in vitro, accounting for biolog- ical ALPS phenotypes in vivo. It also impairs Fas-independent signaling pathways. The observed bacterial infections result partly from functionalhyposplenism, and viral infections result from impaired interferon immunity. We describe here a complex clinical disorder, its genetic basis, and some of the key mechanisms underlying its pathogenesis. Our findings highlight the key role of FADD in Fas-depen- dent and Fas–independent signaling pathways in humans. Germline mutations in FASL 1 (MIM 134638) and FAS 2,3 (MIM 134637) are genetic etiologies of autoimmune lym- phoproliferative syndrome (ALPS [MIM 601859]) in hu- mans. ALPS typically begins in early childhood (median age at onset: 2 yrs), with lymphadenopathy and/or spleno- megaly. About half the patients have autoimmune disease, autoimmune cytopenias being particularly common. 4,5 The patients do not suffer from unusually severe infection, unless they are on immunosuppressive treatment, 4 and display no overt developmental phenotype. We investi- gated the molecular basis of a condition affecting at least four members of an extended consanguineous kindred of Pakistani origin (Figure 1A) with biological features of ALPS (high-circulating CD4  CD8  TCRab þ T-cell [DNT] counts, and elevated IL-10 and FasL serum levels), no clin- ical features of ALPS, a complex infectious phenotype with both viral and bacterial infections, and congenital cardio- vascular malformations (Table 1 and Table S1 available on- line). This study was approved by the local institutional review board. Written informed consent for participation in the study was obtained from all patients and family members studied. The affected children suffered from recurrent, stereotyp- ical episodes of fever, encephalopathy, and mild liver dysfunction (modestly elevated transaminases without cholestasis, metabolic derangement, or synthetic defects), sometimes accompanied by generalized seizures that were difficult to control. Episodes lasted several days, sometimes requiring intensive care, and cranial imaging in three patients (P1, P3, and P4 [IV.2, IV.4, and IV.5 in Figure 1]) suggested atrophy, despite subsequent recovery in two of these patients (P1 and P3). For some of the episodes, it was possible to identify a viral trigger: varicella zoster virus (VZV), measles mumps rubella (MMR) attenuated vaccine, parainfluenza virus, and Epstein-Barr virus (EBV). The index case, P3 (IV.4 in Figure 1), died at the age of 4 yrs, during such an episode. In addition, fatal invasive pneu- mococcal disease occurred in two children (P1 and P2 [IV.2 and IV.3 in Figure 1]), and Howell-Jolly bodies were detected in the two remaining patients (P3 and P4 [IV.4 and IV.5 in Figure 1]), despite the presence of a spleen (indicating functional hyposplenism). 6–8 This clinical syndrome has never before been described (no MIM number). In the previous generation, another five family 1 St Giles Laboratory of Human Genetics of Infectious Diseases, Rockefeller Branch, The Rockefeller University, New York, NY 10065, USA; 2 Institute of Cellular Medicine, Newcastle University Medical School, Newcastle upon Tyne NE2 4HH, UK; 3 Wellchild Paediatric Research Centre and Centre for Rare Diseases and Personalised Medicine, School of Clinical and Experimental Medicine , University of Birmingham College of Medical and Dental Sciences, Edgbaston, Birmingham B152TT, UK; 4 Apoptosis and Cell Death Research Program, Sanford Burnham Medical Research Institute, La Jolla, CA 92037, USA; 5 Laboratory of Human Genetics of Infectious Diseases, Necker Branch, Institut National de la Sante ´ et de la Recherche Me ´dicale, U980, Univer- sity Paris Descartes, Paris 75015, France; 6 Northern Institute for Cancer Research, Newcastle University and Department of Cellular Pathology, Newcastle upon Tyne Hospitals, Newcastle upon Tyne NE2 4HH, UK; 7 Normal and Pathologic Development of the Immune System Research Laboratory, U768, In- stitut National de la Sante ´ et de la Recherche Me ´dicale (INSERM); Unit of Pediatric Immunology and Hematology, Necker Hospital (APHP); University Paris Descartes, Paris 75015, France; 8 Paediatric Neurology Dept, Great North Children’s Hospital, Newcastle upon Tyne NE1 4LP, UK; 9 Children’s Unit, Airedale General Hospital, West Yorkshire BD20 6TD, UK; 10 Paediatric Immunology Dept, Great North Children’s Hospital, Newcastle upon Tyne NE1 4LP, UK; 11 West Midlands Region Genetics Service, Birmingham Women’s Hospital, Edgbaston, Birmingham B152TG, UK; 12 Pediatric Immunology-Hematology Unit, Necker Hospital for Sick Children, Paris 75015, France 13 These authors contributed equally to this work *Correspondence: jean-laurent.casanova@rockefeller.edu DOI 10.1016/j.ajhg.2010.10.028. Ó2010 by The American Society of Human Genetics. All rights reserved. The American Journal of Human Genetics 87, 873–881, December 10, 2010 873