KBP-cytoskeleton interactions underlie developmental anomalies in Goldberg-Shprintzen syndrome.

Goldberg-Shprintzen syndrome (GOSHS, MIM #609460) is an autosomal recessive disorder of intellectual disability, specific facial gestalt and Hirschsprung's disease (HSCR). In 2005, homozygosity mapping in a large consanguineous family identified KIAA1279 as the disease-causing gene. KIAA1279 encodes KIF-binding protein (KBP), whose function is incompletely understood. Studies have identified either the mitochondria or the cytoskeleton as the site of KBP localization and interactions. To better delineate the KIAA1279-related clinical spectrum and the molecular mechanisms involved in GOSHS, we studied five new patients from three different families. The homozygous KIAA1279 mutations in these patients (p.Arg90X, p.Ser200X or p.Arg202IlefsX2) led to nonsense-mediated mRNA decay and loss of KBP function. Despite the absence of functional KBP, respiratory chain complex activity in patient fibroblasts was normal. KBP did not co-localize with mitochondria in control human fibroblasts, but interacted with the actin and tubulin cytoskeleton. KBP expression directly affected neurite growth in a neuron-like cell line (human neuroblastoma SH-SY5Y), in keeping with the central (polymicrogyria) and enteric (HSCR) neuronal developmental defects seen in GOSHS patients. The KBP interactions with actin filaments and microtubules (MTs) demonstrated in our study constitute the first evidence that an actin MT cross-link protein is involved in neuronal development in humans.

ZEB2 zinc-finger missense mutations lead to hypomorphic alleles and a mild Mowat-Wilson syndrome.

Mowat-Wilson syndrome (MWS) is a severe intellectual disability (ID)-distinctive facial gestalt-multiple congenital anomaly syndrome, commonly associating microcephaly, epilepsy, corpus callosum agenesis, conotruncal heart defects, urogenital malformations and Hirschsprung disease (HSCR). MWS is caused by de novo heterozygous mutations in the ZEB2 gene. The majority of mutations lead to haplo-insufficiency through premature stop codons or large gene deletions. Only three missense mutations have been reported so far; none of which resides in a known functional domain of ZEB2. In this study, we report and analyze the functional consequences of three novel missense mutations, p.Tyr1055Cys, p.Ser1071Pro and p.His1045Arg, identified in the highly conserved C-zinc-finger (C-ZF) domain of ZEB2. Patients' phenotype included the facial gestalt of MWS and moderate ID, but no microcephaly, heart defects or HSCR. In vitro studies showed that all the three mutations prevented binding and repression of the E-cadherin promoter, a characterized ZEB2 target gene. Taking advantage of the zebrafish morphant technology, we performed rescue experiments using wild-type (WT) and mutant human ZEB2 mRNAs. Variable, mutation-dependent, embryo rescue, correlating with the severity of patients' phenotype, was observed. Our data provide evidence that these missense mutations cause a partial loss of function of ZEB2, suggesting that its role is not restricted to repression of E-cadherin. Functional domains other than C-ZF may play a role in early embryonic development. Finally, these findings broaden the clinical spectrum of ZEB2 mutations, indicating that MWS ought to be considered in patients with lesser degrees of ID and a suggestive facial gestalt, even in the absence of congenital malformation.