Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant

Abstract

Lissencephaly is a malformation of cortical development typically caused by deficient neuronal migration resulting in cortical thickening and reduced gyration. Here we describe a "thin" lissencephaly (TLIS) variant characterized by megalencephaly, frontal predominant pachygyria, intellectual disability, and seizures. Trio-based whole-exome sequencing and targeted re-sequencing identified recessive mutations of CRADD in six individuals with TLIS from four unrelated families of diverse ethnic backgrounds. CRADD (also known as RAIDD) is a death-domain-containing adaptor protein that oligomerizes with PIDD and caspase-2 to initiate apoptosis. TLIS variants cluster in the CRADD death domain, a platform for interaction with other death-domain-containing proteins including PIDD. Although caspase-2 is expressed in the developing mammalian brain, little is known about its role in cortical development. CRADD/caspase-2 signaling is implicated in neurotrophic factor withdrawal- and amyloid-β-induced dendritic spine collapse and neuronal apoptosis, suggesting a role in cortical sculpting and plasticity. TLIS-associated CRADD variants do not disrupt interactions with caspase-2 or PIDD in co-immunoprecipitation assays, but still abolish CRADD's ability to activate caspase-2, resulting in reduced neuronal apoptosis in vitro. Homozygous Cradd knockout mice display megalencephaly and seizures without obvious defects in cortical lamination, supporting a role for CRADD/caspase-2 signaling in mammalian brain development. Megalencephaly and lissencephaly associated with defective programmed cell death from loss of CRADD function in humans implicate reduced apoptosis as an important pathophysiological mechanism of cortical malformation. Our data suggest that CRADD/caspase-2 signaling is critical for normal gyration of the developing human neocortex and for normal cognitive ability.

Lissencephaly: Expanded imaging and clinical classification

“…Subsequent work by many groups has to date identified 19 LIS-SBH associated genes including LIS1 , many of which are microtubule structural (tubulin) or microtubule-associated proteins (MAPs), including: ACTB, ACTG1, ARX, CDK5, CRADD, DCX, DYNC1H1, KIF2A, KIF5C, LIS1, NDE1, RELN, TUBA1A, TUBA8, TUBB, TUBB2B, TUBB3, TUBG1 , and VLDLR [Abdollahi et al, 2009; Boycott et al, 2009; Breuss et al, 2012; Di Donato et al, 2016a; Gleeson et al, 1998; Hong et al, 2000; Jaglin et al, 2009; Keays et al, 2007; Kitamura et al, 2002; Magen et al, 2015; Poirier et al, 2013a; Poirier et al, 2010; Reiner et al, 1993; Riviere et al, 2012; Willemsen et al, 2012]. We include NDE1 , as the associated gyral malformation resembles tubulinopathy-associated dysgyria [Paciorkowski, 2013 PMID 23704059].…”

Genetics and mechanisms leading to human cortical malformations

“…Cases are often atypical, sometimes exhibiting de novo sporadic mutations, or alternatively, homozygous mutations were identified in consanguineous families. Some examples are EML1, CRADD, ACTG1 and KATNB1 (see Table 6) [267][268][269][270][271]. Related genes, such as α-E-catenin, Ccdc85C, Rapgef2/Rapgef6, Afadin and RhoA induce similar, severe phenotypes (e.g.…”

“…These data suggest that CRADD/caspase-2 signaling is required for normal development of the human neocortex and for normal cognitive function. Decreased caspase-2-mediated apoptosis during human development results in this MCD [268].…”

“…More recently, an interesting study identified a mild variant of lissencephaly, after review of more than 1,400 LIS phenotype patients [268]. The phenotype was referred to as TLIS or ''thin" lissencephaly, and is characterized by anterior-predominant pachygyria with shallow and unusually wide sulci, a mildly thick cortex (5-7 mm) in at least the frontal regions and megaencephaly.…”

Novel candidate genes and variants underlying autosomal recessive neurodevelopmental disorders with intellectual disability

“…Unless indicated, these variants were absent in 194 unrelated Pakistani exomes with non-cognitive Mendelian phenotypes and in ~ 1000 unrelated individuals in the GME Variome Project. References per known gene: ALG3 (Riess et al 2013); ASPM (Kousar et al 2010); BCKDK (Novarino et al 2012); CRADD (Di Donato et al 2016; Harel et al 2017); CWF19L1 (Burns et al 2014; Nguyen et al 2016; Evers et al 2016); CYB5R3 (Ewenczyk et al 2008); GAN (Kuhlenbäumer et al 2002; Tazir et al 2009); LRP2 (Vasli et al 2016); MBOAT7 (Johansen et al 2016); MLYCD (Salomons et al 2007); PNKP (Shen et al 2010); SPTBN2 (Lise et al 2012); TUSC3 (Garshasbi et al 2008, 2011; Khan et al 2011; Loddo et al 2013; Al-Amri et al 2016); WDR62 (Wang et al 2017). …”