Dominant mutations in ROR2, encoding an orphan receptor tyrosine kinase, cause brachydactyly type B

Inherited limb malformations provide a valuable resource for the identification of genes involved in limb development. Brachydactyly type B (BDB), an autosomal dominant disorder, is the most severe of the brachydactylies and characterized by terminal deficiency of the fingers and toes. In the typical form of BDB, the thumbs and big toes are spared, sometimes with broadening or partial duplication. The BDB1 locus was previously mapped to chromosome 9q22 within an interval of 7.5 cM (refs 9,10). Here we describe mutations in ROR2, which encodes the orphan receptor tyrosine kinase ROR2 (ref. 11), in three unrelated families with BDB1. We identified distinct heterozygous mutations (2 nonsense, 1 frameshift) within a 7-amino-acid segment of the 943-amino-acid protein, all of which predict truncation of the intracellular portion of the protein immediately after the tyrosine kinase domain. The localized nature of these mutations suggests that they confer a specific gain of function. We obtained further evidence for this by demonstrating that two patients heterozygous for 9q22 deletions including ROR2 do not exhibit BDB. Expression of the mouse mouse orthologue, Ror2, early in limb development indicates that BDB arises as a primary defect of skeletal patterning.     

Mutant glycosyltransferase and altered glycosylation of alpha-dystroglycan in the myodystrophy mouse

Spontaneous and engineered mouse mutants have facilitated our understanding of the pathogenesis of muscular dystrophy and they provide models for the development of therapeutic approaches. The mouse myodystrophy (myd) mutation produces an autosomal recessive, neuromuscular phenotype. Homozygotes have an abnormal gait, show abnormal posturing when suspended by the tail and are smaller than littermate controls. Serum creatine kinase is elevated and muscle histology is typical of a progressive myopathy with focal areas of acute necrosis and clusters of regenerating fibers. Additional aspects of the phenotype include sensorineural deafness, reduced lifespan and decreased reproductive fitness. The myd mutation maps to mouse chromosome 8 at approximately 33 centimorgans (cM) (refs. 2, 4-7). Here we show that the gene mutated in myd encodes a glycosyltransferase, Large. The human homolog of this gene (LARGE) maps to chromosome 22q. In myd, an intragenic deletion of exons 4-7 causes a frameshift in the resultant mRNA and a premature termination codon before the first of the two catalytic domains. On immunoblots, a monoclonal antibody to alpha-dystroglycan (a component of the dystrophin-associated glycoprotein complex) shows reduced binding in myd, which we attribute to altered glycosylation of this protein. We speculate that abnormal post-translational modification of alpha-dystroglycan may contribute to the myd phenotype.     

Defects in whirlin,a PDZ domain molecule involved in stereocilia elongation,cause deafness in the whirler mouse and families with DFNB31

The whirler mouse mutant (wi) does not respond to sound stimuli, and detailed ultrastructural analysis of sensory hair cells in the organ of Corti of the inner ear indicates that the whirler gene encodes a protein involved in the elongation and maintenance of stereocilia in both inner hair cells (IHCs) and outer hair cells (OHCs). BAC-mediated transgene correction of the mouse phenotype and mutation analysis identified the causative gene as encoding a novel PDZ protein called whirlin. The gene encoding whirlin also underlies the human autosomal recessive deafness locus DFNB31. In the mouse cochlea, whirlin is expressed in the sensory IHC and OHC stereocilia. Our findings suggest that this novel PDZ domain-containing molecule acts as an organizer of submembranous molecular complexes that control the coordinated actin polymerization and membrane growth of stereocilia.     

Recessive Robinow syndrome, allelic to dominant brachydactyly type B, is caused by mutation of ROR2

The autosomal recessive form of Robinow syndrome (RRS; MIM 268310) is a severe skeletal dysplasia with generalized limb bone shortening, segmental defects of the spine, brachydactyly and a dysmorphic facial appearance. We previously mapped the gene mutated in RRS to chromosome 9q22 (ref. 4), a region that overlaps the locus for autosomal dominant brachydactyly type B (refs 5,6). The recent identification of ROR2, encoding an orphan receptor tyrosine kinase, as the gene mutated in brachydactyly type B (BDB1; ref. 7) and the mesomelic dwarfing in mice homozygous for a lacZ and/or a neo insertion into Ror2 (refs 8,9) made this gene a candidate for RRS. Here we report homozygous missense mutations in both intracellular and extracellular domains of ROR2 in affected individuals from 3 unrelated consanguineous families, and a nonsense mutation that removes the tyrosine kinase domain and all subsequent 3' regions of the gene in 14 patients from 7 families from Oman. The nature of these mutations suggests that RRS is caused by loss of ROR2 activity. The identification of mutations in three distinct domains (containing Frizzled-like, kringle and tyrosine kinase motifs) indicates that these are all essential for ROR2 function.     

Common variants near ATM are associated with glycemic response to metformin in type 2 diabetes

Metformin is the most commonly used pharmacological therapy for type 2 diabetes. We report a genome-wide association study for glycemic response to metformin in 1,024 Scottish individuals with type 2 diabetes with replication in two cohorts including 1,783 Scottish individuals and 1,113 individuals from the UK Prospective Diabetes Study. In a combined meta-analysis, we identified a SNP, rs11212617, associated with treatment success (n = 3,920, P = 2.9 × 10(-9), odds ratio = 1.35, 95% CI 1.22-1.49) at a locus containing ATM, the ataxia telangiectasia mutated gene. In a rat hepatoma cell line, inhibition of ATM with KU-55933 attenuated the phosphorylation and activation of AMP-activated protein kinase in response to metformin. We conclude that ATM, a gene known to be involved in DNA repair and cell cycle control, plays a role in the effect of metformin upstream of AMP-activated protein kinase, and variation in this gene alters glycemic response to metformin.     

A mutation in OTOF, encoding otoferlin, a FER-1-like protein, causes DFNB9, a nonsyndromic form of deafness

Using a candidate gene approach, we identified a novel human gene, OTOF, underlying an autosomal recessive, nonsyndromic prelingual deafness, DFNB9. The same nonsense mutation was detected in four unrelated affected families of Lebanese origin. OTOF is the second member of a mammalian gene family related to Caenorhabditis elegans fer-1. It encodes a predicted cytosolic protein (of 1,230 aa) with three C2 domains and a single carboxy-terminal transmembrane domain. The sequence homologies and predicted structure of otoferlin, the protein encoded by OTOF, suggest its involvement in vesicle membrane fusion. In the inner ear, the expression of the orthologous mouse gene, mainly in the sensory hair cells, indicates that such a role could apply to synaptic vesicles.     

Msh2 deficiency prevents in vivo somatic instability of the CAG repeat in Huntington disease transgenic mice

Huntington disease (HD), an autosomal dominant, progressive neurodegenerative disorder, is caused by an expanded CAG repeat sequence leading to an increase in the number of glutamine residues in the encoded protein. The normal CAG repeat range is 5-36, whereas 38 or more repeats are found in the diseased state; the severity of disease is roughly proportional to the number of CAG repeats. HD shows anticipation, in which subsequent generations display earlier disease onsets due to intergenerational repeat expansion. For longer repeat lengths, somatic instability of the repeat size has been observed both in human cases at autopsy and in transgenic mouse models containing either a genomic fragment of human HD exon 1 (ref. 9) or an expanded repeat inserted into the endogenous mouse gene Hdh (ref. 10). With increasing repeat number, the protein changes conformation and becomes increasingly prone to aggregation, suggesting important functional correlations between repeat length and pathology. Because dinucleotide repeat instability is known to increase when the mismatch repair enzyme MSH2 is missing, we examined instability of the HD CAG repeat by crossing transgenic mice carrying exon 1 of human HD (ref. 16) with Msh2-/- mice. Our results show that Msh2 is required for somatic instability of the CAG repeat.     

Hermansky-Pudlak syndrome type 7 (HPS-7) results from mutant dysbindin,a member of the biogenesis of lysosome-related organelles complex 1 (BLOC-1)

Hermansky-Pudlak syndrome (HPS; MIM 203300) is a genetically heterogeneous disorder characterized by oculocutaneous albinism, prolonged bleeding and pulmonary fibrosis due to abnormal vesicle trafficking to lysosomes and related organelles, such as melanosomes and platelet dense granules. In mice, at least 16 loci are associated with HPS, including sandy (sdy; ref. 7). Here we show that the sdy mutant mouse expresses no dysbindin protein owing to a deletion in the gene Dtnbp1 (encoding dysbindin) and that mutation of the human ortholog DTNBP1 causes a novel form of HPS called HPS-7. Dysbindin is a ubiquitously expressed protein that binds to alpha- and beta-dystrobrevins, components of the dystrophin-associated protein complex (DPC) in both muscle and nonmuscle cells. We also show that dysbindin is a component of the biogenesis of lysosome-related organelles complex 1 (BLOC-1; refs. 9-11), which regulates trafficking to lysosome-related organelles and includes the proteins pallidin, muted and cappuccino, which are associated with HPS in mice. These findings show that BLOC-1 is important in producing the HPS phenotype in humans, indicate that dysbindin has a role in the biogenesis of lysosome-related organelles and identify unexpected interactions between components of DPC and BLOC-1.     

The hyh mutation uncovers roles for alpha Snap in apical protein localization and control of neural cell fate

The hyh (hydrocephalus with hop gait) mouse shows a markedly small cerebral cortex at birth and dies postnatally from progressive enlargement of the ventricular system. Here we show that the small hyh cortex reflects altered cell fate. Neural progenitor cells withdraw prematurely from the cell cycle, producing more early-born, deep-layer cerebral cortical neurons but depleting the cortical progenitor pool, such that late-born, upper-layer cortical neurons are underproduced, creating a small cortex. hyh mice carry a hypomorphic missense mutation in the gene Napa encoding soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein alpha (alpha Snap), involved in SNAP receptor (SNARE)-mediated vesicle fusion in many cellular contexts. A targeted null Napa mutation is embryonically lethal. Altered neural cell fate is accompanied by abnormal localization of many apical proteins implicated in regulation of neural cell fate, including E-cadherin, beta-catenin, atypical protein kinase C (aPKC) and INADL (inactivation-no-afterpotential D-like, also known as protein associated with Lin7, or Pals1). Apical localization of the SNARE Vamp7 is also disrupted. Thus, alpha Snap is essential for apical protein localization and cell fate determination in neuroepithelial cells.