Hereditary Multiple Exostoses—A Review of the Molecular Background, Diagnostics, and Potential Therapeutic Strategies

Hereditary multiple exostoses (HMEs) syndrome, also known as multiple osteochondromas, represents a rare and severe human skeletal disorder. The disease is characterized by multiple benign cartilage-capped bony outgrowths, termed exostoses or osteochondromas, that locate most commonly in the juxta-epiphyseal portions of long bones. Affected individuals usually complain of persistent pain caused by the pressure on neighboring tissues, disturbance of blood circulation, or rarely by spinal cord compression. However, the most severe complication of this condition is malignant transformation into chondrosarcoma, occurring in up to 3.9% of HMEs patients. The disease results mainly from heterozygous loss-of-function alterations in the EXT1 or EXT2 genes, encoding Golgi-associated glycosyltransferases, responsible for heparan sulfate biosynthesis. Some of the patients with HMEs do not carry pathogenic variants in those genes, hence the presence of somatic mutations, deep intronic variants, or another genes/loci is suggested. This review presents the systematic analysis of current cellular and molecular concepts of HMEs along with clinical characteristics, clinical and molecular diagnostic methods, differential diagnosis, and potential treatment options.

The Largest Germline Heterozygous Deletion Encompassing Potocki–Shaffer and WAGR Syndromes Loci to Date: A Case Report

Potocki–Schaffer syndrome includes multiple exostoses, parietal foramina, and variable developmental delay/intellectual disability. It is associated with a heterozygous deletion of the 11p12p11.2 region. In some cases, the deletion extends to the WAGR locus (11p13p12). We describe here a 9-month-old girl harboring the largest germline heterozygous deletion characterized so far. Oligohydramnios and parietal foramina were noticed during pregnancy. No patient has been diagnosed before with concomitance of these two syndromes during the prenatal period. Cytogenetic diagnosis was anticipated on basis of clinical and radiological signs. Postnatal conventional karyotype confirmed an interstitial 11p deletion: 46,XX,del(11)(p11.2p15.1). Array-comparative genomic hybridization characterized a 29.6 Mb deletion. Our case illustrates the interest of high-resolution genomic approaches to correlate adequately clinical phenotypes with specific genes in suspected contiguous gene deletion syndromes.

Identification of a Novel EXT Mutation in A Kindred With Hereditary Multiple Exostoses Using Whole-Exome Sequencing and Overview of Mutation Spectrum

Background: Hereditary Multiple Osteochondromas(HMO) is a rare genetic musculoskeletal disorder characterized by multiple osteochondromas that form near to the growth plates of many bones. Loss-of-function mutations in EXT1 or EXT2 that encode glycosyltrasferases are the causal mutations for most HMO patients.Methods: After collecting the family history and clinical information, we used Whole-Exome Sequencing to find the pathogenic mutations in one Chinese Hereditary Multiple Exostoses pedigree. Sanger sequencing and relevant online databases were used to validate the screened variants. Lollipop plots were drew to map the reported mutations from online databases (Multiple Osteochondroma Mutation Database and clinvar)on a linear protein domains by MutationMapper.Results: A novel heterozygous splicing-site mutation in gene EXT1 (NM_000127:exon5:c.1417+1G>C，chr8:118834703) was found in this pedigree and mutation spectrum of genes EXT1 and EXT2 were demonstrated.Conclusions: Our results help this pedigree to identify the pathogenic variant and guide the prenatal diagnosis, also expand the mutation spectrum in Hereditary Multiple Osteochondromas.

Congenital Disorders of Deficiency in Glycosaminoglycan Biosynthesis

Glycosaminoglycans (GAGs) including chondroitin sulfate, dermatan sulfate, and heparan sulfate are covalently attached to specific core proteins to form proteoglycans, which are distributed at the cell surface as well as in the extracellular matrix. Proteoglycans and GAGs have been demonstrated to exhibit a variety of physiological functions such as construction of the extracellular matrix, tissue development, and cell signaling through interactions with extracellular matrix components, morphogens, cytokines, and growth factors. Not only connective tissue disorders including skeletal dysplasia, chondrodysplasia, multiple exostoses, and Ehlers-Danlos syndrome, but also heart and kidney defects, immune deficiencies, and neurological abnormalities have been shown to be caused by defects in GAGs as well as core proteins of proteoglycans. These findings indicate that GAGs and proteoglycans are essential for human development in major organs. The glycobiological aspects of congenital disorders caused by defects in GAG-biosynthetic enzymes including specific glysocyltransferases, epimerases, and sulfotransferases, in addition to core proteins of proteoglycans will be comprehensively discussed based on the literature to date.