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Eur J Hum Genet. 2016 Feb;24(2):198-207. doi: 10.1038/ejhg.2015.91. Epub 2015 May 13.

A novel phenotype in N-glycosylation disorders: Gillessen-Kaesbach-Nishimura skeletal dysplasia due to pathogenic variants in ALG9.

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Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden.
Department of Clinical Genetics, Karolinska University Hospital, Stockholm, Sweden.
Experimental Pediatrics, Clinical Sciences, Lund University, Lund, Sweden.
Department of Clinical Chemistry, part of University Health Care in Region Skåne, Lund, Sweden.
Department of Pediatric Radiology, Karolinska University Hospital, Stockholm, Sweden.
Department of Obstetrics and Gynecology, Karolinska University Hospital, Stockholm, Sweden.
Department of Woman and Child Health, Karolinska Institutet, Stockholm, Sweden.
Centre for Inherited Metabolic Diseases, Karolinska University Hospital, Stockholm, Sweden.
Department of Neuropediatrics, Karolinska University Hospital, Stockholm, Sweden.
Section for Perinatal Pathology, Department of Pathology, Karolinska University Hospital and Karolinska Institutet, Stockholm, Sweden.
Department of Pediatric Imaging, Tokyo Metropolitan Children's Medical Center, Tokyo, Japan.


A rare lethal autosomal recessive syndrome with skeletal dysplasia, polycystic kidneys and multiple malformations was first described by Gillessen-Kaesbach et al and subsequently by Nishimura et al. The skeletal features uniformly comprise a round pelvis, mesomelic shortening of the upper limbs and defective ossification of the cervical spine. We studied two unrelated families including three affected fetuses with Gillessen-Kaesbach-Nishimura syndrome using whole-exome and Sanger sequencing, comparative genome hybridization and homozygosity mapping. All affected patients were shown to have a novel homozygous splice variant NM_024740.2: c.1173+2T>A in the ALG9 gene, encoding alpha-1,2-mannosyltransferase, involved in the formation of the lipid-linked oligosaccharide precursor of N-glycosylation. RNA analysis demonstrated skipping of exon 10, leading to shorter RNA. Mass spectrometric analysis showed an increase in monoglycosylated transferrin as compared with control tissues, confirming that this is a congenital disorder of glycosylation (CDG). Only three liveborn children with ALG9-CDG have been previously reported, all with missense variants. All three suffered from intellectual disability, muscular hypotonia, microcephaly and renal cysts, but none had skeletal dysplasia. Our study shows that some pathogenic variants in ALG9 can present as a lethal skeletal dysplasia with visceral malformations as the most severe phenotype. The skeletal features overlap with that previously reported for ALG3- and ALG12-CDG, suggesting that this subset of glycosylation disorders constitutes a new diagnostic group of skeletal dysplasias.

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