SCUBE3 loss-of-function causes a recognizable recessive developmental disorder due to defective bone morphogenetic protein signaling.

Signal peptide-CUB-EGF domain-containing protein 3 (SCUBE3) is a member of a small family of multifunctional cell surface-anchored glycoproteins functioning as co-receptors for a variety of growth factors. Here we report that bi-allelic inactivating variants in SCUBE3 have pleiotropic consequences on development and cause a previously unrecognized syndromic disorder. Eighteen affected individuals from nine unrelated families showed a consistent phenotype characterized by reduced growth, skeletal features, distinctive craniofacial appearance, and dental anomalies. In vitro functional validation studies demonstrated a variable impact of disease-causing variants on transcript processing, protein secretion and function, and their dysregulating effect on bone morphogenetic protein (BMP) signaling. We show that SCUBE3 acts as a BMP2/BMP4 co-receptor, recruits the BMP receptor complexes into raft microdomains, and positively modulates signaling possibly by augmenting the specific interactions between BMPs and BMP type I receptors. Scube3-/- mice showed craniofacial and dental defects, reduced body size, and defective endochondral bone growth due to impaired BMP-mediated chondrogenesis and osteogenesis, recapitulating the human disorder. Our findings identify a human disease caused by defective function of a member of the SCUBE family, and link SCUBE3 to processes controlling growth, morphogenesis, and bone and teeth development through modulation of BMP signaling.

The clinical and genetic Spectrum of Maroteaux-Lamy syndrome (Mucopolysaccharidosis VI) in the Eastern Province of Saudi Arabia.

Mucopolysaccharidosis (MPS VI) or Maroteaux-Lamy syndrome is an autosomal recessive lysosomal storage disease caused by deficiency of the enzyme N-acetylgalactosamine 4-sulfatase or arylsulfatase B. It is involved in the degradation of glycosaminoglycans and characterized by a wide spectrum of clinical and genetic heterogeneity. So far, more than 150 mutations have been reported in the ARSB gene. Most of these mutations are either novel, private, or compound heterozygous making phenotype-genotype correlation as well as population screening difficult. The aim of our study is to determine the genotypes and phenotypes of MPS VI among the Saudi population at the Eastern Province of Saudi Arabia. The clinical data of all the patients seen and diagnosed with MPS VI (Maroteaux-Lamy syndrome) at the main hospital from January 1, 1983, to December 31, 2016, were reviewed. A total of 18 patients from 6 unrelated consanguineous families (first-cousin parents) were diagnosed with MPS VI during the defined 33 years. All of the affected patients displayed the severe phenotype of MPS VI. Only one genotype (c.753C > Gp.Y251X) was identified among five of the studied families. All of those families were inhabitants of Al-Hofuf area, but they descended from different clans. A second genotype (c270_274del5bp pc.91Afs*34) was detected in a single family who had originated from Abha area (the southern-west region of the country). This report demonstrated the homogeneity for both phenotype and genotype of our studied patients with MPS VI. This may eventually make selective asymptomatic carrier test and newborn screening highly feasible in this region of country.

Biallelic loss of human CTNNA2, encoding αN-catenin, leads to ARP2/3 complex overactivity and disordered cortical neuronal migration.

Neuronal migration defects, including pachygyria, are among the most severe developmental brain defects in humans. Here, we identify biallelic truncating mutations in CTNNA2, encoding αN-catenin, in patients with a distinct recessive form of pachygyria. CTNNA2 was expressed in human cerebral cortex, and its loss in neurons led to defects in neurite stability and migration. The αN-catenin paralog, αE-catenin, acts as a switch regulating the balance between ß-catenin and Arp2/3 actin filament activities1. Loss of αN-catenin did not affect ß-catenin signaling, but recombinant αN-catenin interacted with purified actin and repressed ARP2/3 actin-branching activity. The actin-binding domain of αN-catenin or ARP2/3 inhibitors rescued the neuronal phenotype associated with CTNNA2 loss, suggesting ARP2/3 de-repression as a potential disease mechanism. Our findings identify CTNNA2 as the first catenin family member with biallelic mutations in humans, causing a new pachygyria syndrome linked to actin regulation, and uncover a key factor involved in ARP2/3 repression in neurons.

Nail-Patella Syndrome: A Report of a Saudi Arab Family With an Autosomal Recessive Inheritance.

BACKGROUND: Nail-patella syndrome (NPS) is an autosomal dominant disorder with a variable interfamilial and intrafamilial clinical expressivity and penetrance. It is caused by loss-of-function heterozygous mutation in the LIM-homeodomain transcription factor (LMX1B) located on chromosome 9q. The pleiotropic LMB1X gene, a member of the homeogene family, is involved in the development of glomerular basement membrane, dorsoventral limb structures, along with the nails and the anterior segment of the eye. OBJECTIVE: Here, we report a Saudi Arab consanguineous family with 2 affected sisters presented with the typical nail changes of NPS. METHODS: DNA samples were collected from the sisters and their parents after consent. RESULTS: Both sisters were found to be homozygous for a previously described disease-causing mutation (c.268C>T) at the (LMX1B) gene. Both of the phenotypically normal parents were confirmed to be heterozygous for the same mutation. CONCLUSION: This finding supports the autosomal recessive mode of inheritance in this family.