From Proteopediaproteopedia link
FADD DEATH EFFECTOR DOMAIN, F25Y MUTANT, NMR MINIMIZED AVERAGE STRUCTURE
[FADD_HUMAN] Defects in FADD are the cause of infections recurrent associated with encephalopathy hepatic dysfunction and cardiovascular malformations (IEHDCM) [MIM:613759]. A condition with biological features of autoimmune lymphoproliferative syndrome such as high-circulating CD4(-)CD8(-)TCR-alpha-beta(+) T-cell counts, and elevated IL10 and FASL levels. Affected individuals suffer from recurrent, stereotypical episodes of fever, encephalopathy, and mild liver dysfunction sometimes accompanied by generalized seizures. The episodes can be triggered by varicella zoster virus (VZV), measles mumps rubella (MMR) attenuated vaccine, parainfluenza virus, and Epstein-Barr virus (EBV).
[FADD_HUMAN] Apoptotic adaptor molecule that recruits caspase-8 or caspase-10 to the activated Fas (CD95) or TNFR-1 receptors. The resulting aggregate called the death-inducing signaling complex (DISC) performs caspase-8 proteolytic activation. Active caspase-8 initiates the subsequent cascade of caspases mediating apoptosis. Involved in interferon-mediated antiviral immune response, playing a role in the positive regulation of interferon signaling.   
Publication Abstract from PubMed
When activated, membrane-bound receptors for Fas and tumour-necrosis factor initiate programmed cell death by recruiting the death domain of the adaptor protein FADD to the membrane. FADD then activates caspase 8 (also known as FLICE or MACH) through an interaction between the death-effector domains of FADD and caspase 8. This ultimately leads to the apoptotic response. Death-effector domains and homologous protein modules known as caspase-recruitment domains have been found in several proteins and are important regulators of caspase (FLICE) activity and of apoptosis. Here we describe the solution structure of a soluble, biologically active mutant of the FADD death-effector domain. The structure consists of six antiparallel, amphipathic alpha-helices and resembles the overall fold of the death domains of Fas and p75. Despite this structural similarity, mutations that inhibit protein-protein interactions involving the Fas death domain have no effect when introduced into the FADD death-effector domain. Instead, a hydrophobic region of the FADD death-effector domain that is not present in the death domains is vital for binding to FLICE and for apoptotic activity.
NMR structure and mutagenesis of the FADD (Mort1) death-effector domain.,Eberstadt M, Huang B, Chen Z, Meadows RP, Ng SC, Zheng L, Lenardo MJ, Fesik SW Nature. 1998 Apr 30;392(6679):941-5. PMID:9582077
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.