Deletion of exon 8 from the EXT1 gene causes multiple osteochondromas (MO) in a family with three affected members.

Lei Zhuang,Stefan Kuchen,Peter M Villiger,Simon D Gerber,Beat Trueb

doi:10.1186/s40064-016-1695-6

Lei Zhuang, Stefan Kuchen + Show 3 more

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https://doi.org/10.1186/s40064-016-1695-6

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Abstract

Multiple osteochondromas (also called hereditary multiple exostoses) is an autosomal dominant disorder characterized by multiple cartilaginous tumors, which are caused by mutations in the genes for exostosin-1 (EXT1) and exostosin-2 (EXT2). The goal of this study was to elucidate the genetic alterations in a family with three affected members. Isolation of RNA from the patients’ blood followed by reverse transcription and PCR amplification of selected fragments showed that the three patients lack a specific region of 90 bp from their EXT1 mRNA. This region corresponds to the sequence of exon 8 from the EXT1 gene. No splice site mutation was found around exon 8. However, long-range PCR amplification of the region from intron 7 to intron 8 indicated that the three patients contain a deletion of 4318 bp, which includes exon 8 and part of the flanking introns. There is evidence that the deletion was caused by non-homologous end joining because the breakpoints are not located within a repetitive element, but contain multiple copies of the deletion hotspot sequence TGRRKM. Exon 8 encodes part of the active site of the EXT1 enzyme, including the DXD signature of all UDP-sugar glycosyltransferases. It is conceivable that the mutant protein exerts a dominant negative effect on the activity of the EXT glycosyltransferase since it might interact with normal copies of the enzyme to form an inactive hetero-oligomeric complex. We suggest that sequencing of RNA might be superior to exome sequencing to detect short deletions of a single exon.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-1695-6) contains supplementary material, which is available to authorized users.

Highlights

Multiple osteochondromas (MO), called hereditary multiple exostoses (HME), is a genetic, autosomal dominant disorder characterized by multiple benign cartilaginous tumors
In the present work we have studied a patient with MO from a family containing three affected members
At the age of 12, he was diagnosed to suffer from MO based on progressive exostoses at numerous locations, including toes, ankles, knees, hips, ribs, fingers, wrist, elbows and shoulders (Fig. 2b– f )

Summary

Introduction

Multiple osteochondromas (MO), called hereditary multiple exostoses (HME), is a genetic, autosomal dominant disorder characterized by multiple benign cartilaginous tumors These tumors (or exostoses) form next to the growth plate of long bones, ribs and pelvis and protrude into the adjacent perichondrium and neighboring tissue (Huegel et al 2013). Most of the patients have to undergo repetitive surgery to remove some of the MO is caused by heterozygous inactivating mutations of the genes for exostosin-1 (EXT1) or exostosin-2 (EXT2). The majority of these mutations are nonsense, frame shift and splice-site mutations, but there are missense mutations and deletions (Jennes et al 2009; Pedrini et al 2011). That some of these cases might be explained by somatic, mosaic mutations in the EXT genes (loss of heterozygosity) and/or by mutations in some of the large introns (Szuhai et al 2011; Waaijer et al 2013)

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