• Elizabeth Stevens, Keren J Carss, Sebahattin Cirak, A Reghan Foley, Silvia Torelli, Tobias Willer, Dimira E Tambunan, Shu Yau, Lina Brodd, Caroline A Sewry, Lucy Feng, Goknur Haliloglu, Diclehan Orhan, William B Dobyns, Gregory M Enns, Melanie Manning, Amanda Krause, Mustafa A Salih, Christopher A Walsh, Matthew Hurles, Kevin P Campbell, M Chiara Manzini, UK10K Consortium, Derek Stemple, Yung-Yao Lin, and Francesco Muntoni.
• Dubowitz Neuromuscular Centre, UCL Institute of Child Health, London, UK.
• Am. J. Hum. Genet. 2013 Mar 7; 92 (3): 354-65.

AbstractMutations in several known or putative glycosyltransferases cause glycosylation defects in α-dystroglycan (α-DG), an integral component of the dystrophin glycoprotein complex. The hypoglycosylation reduces the ability of α-DG to bind laminin and other extracellular matrix ligands and is responsible for the pathogenesis of an inherited subset of muscular dystrophies known as the dystroglycanopathies. By exome and Sanger sequencing we identified two individuals affected by a dystroglycanopathy with mutations in β-1,3-N-acetylgalactosaminyltransferase 2 (B3GALNT2). B3GALNT2 transfers N-acetyl galactosamine (GalNAc) in a β-1,3 linkage to N-acetyl glucosamine (GlcNAc). A subsequent study of a separate cohort of individuals identified recessive mutations in four additional cases that were all affected by dystroglycanopathy with structural brain involvement. We show that functional dystroglycan glycosylation was reduced in the fibroblasts and muscle (when available) of these individuals via flow cytometry, immunoblotting, and immunocytochemistry. B3GALNT2 localized to the endoplasmic reticulum, and this localization was perturbed by some of the missense mutations identified. Moreover, knockdown of b3galnt2 in zebrafish recapitulated the human congenital muscular dystrophy phenotype with reduced motility, brain abnormalities, and disordered muscle fibers with evidence of damage to both the myosepta and the sarcolemma. Functional dystroglycan glycosylation was also reduced in the b3galnt2 knockdown zebrafish embryos. Together these results demonstrate a role for B3GALNT2 in the glycosylation of α-DG and show that B3GALNT2 mutations can cause dystroglycanopathy with muscle and brain involvement.Copyright © 2013 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.

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