A Recessive Skeletal Dysplasia, SEMD Aggrecan Type, Results from a Missense Mutation Affecting the C-Type Lectin Domain of Aggrecan

Abstract

Analysis of a nuclear family with three affected offspring identified an autosomal-recessive form of spondyloepimetaphyseal dysplasia characterized by severe short stature and a unique constellation of radiographic findings. Homozygosity for a haplotype that was identical by descent between two of the affected individuals identified a locus for the disease gene within a 17.4 Mb interval on chromosome 15, a region containing 296 genes. These genes were assessed and ranked by cartilage selectivity with whole-genome microarray data, revealing only two genes, encoding aggrecan and chondroitin sulfate proteoglycan 4, that were selectively expressed in cartilage. Sequence analysis of aggrecan complementary DNA from an affected individual revealed homozygosity for a missense mutation (c.6799G --> A) that predicts a p.D2267N amino acid substitution in the C-type lectin domain within the G3 domain of aggrecan. The D2267 residue is predicted to coordinate binding of a calcium ion, which influences the conformational binding loops of the C-type lectin domain that mediate interactions with tenascins and other extracellular-matrix proteins. Expression of the normal and mutant G3 domains in mammalian cells showed that the mutation created a functional N-glycosylation site but did not adversely affect protein trafficking and secretion. Surface-plasmon-resonance studies showed that the mutation influenced the binding and kinetics of the interactions between the aggrecan G3 domain and tenascin-C. These findings identify an autosomal-recessive skeletal dysplasia and a significant role for the aggrecan C-type lectin domain in regulating endochondral ossification and, thereby, height.

Identification of a novel heterozygous mutation of the Aggrecan gene in a family with idiopathic short stature and multiple intervertebral disc herniation

“…13 To date, at least 25 pathological ACAN mutations including our case have been reported. [5][6][7][8][9][10][11][12] The autosomal recessive condition in a single family was characterized by extreme short stature (66-71 cm final height) with short necks, barrel chests and craniofacial abnormalities, including macrocephaly, brachydactyly, and mid-face hypoplasia, referred as SEMD aggrecan type. 5 On the other hand, the heterozygous mutations exhibit a broad phenotypic spectrum of short stature associated with advanced bone maturation, early-onset osteoarthritis, and mild dysmorphic features including mid-facial hypoplasia, brachydactyly, broad great toes, and lumbar lordosis, with no apparent genotype-phenotype correlations.…”

“…4 To date, at least 24 pathological ACAN mutations have been identified in patients with highly variable phenotypes, such as spondyloepimetaphyseal dysplasia (SEMD) aggrecan type, spondyloepiphyseal dysplasia Kimberley type, familial osteochondritis dissecans, early-onset osteoarthritis, and short stature with advanced bone maturation. [5][6][7][8][9][10][11][12] We herein report a Japanese family with ISS with a novel heterozygous frameshift mutation in the ACAN gene (c.1744delT; p.Phe582fs*69), providing further evidence that ACAN haploinsufficiency causes short stature with advanced bone maturation. Furthermore, we advocate multiple lumbar disc herniation as a novel phenotype associated with ACAN haploinsufficiency.…”

Next generation sequencing-based mutation screening of 86 patients with idiopathic short stature

“…These four variants were missense substitutions and indels in ACAN. ACAN was initially reported as the causative gene for autosomal recessive spondyloepimetaphyseal dysplasia and autosomal dominant spondyloepiphyseal dysplasia [17,18] and was subsequently implicated in ISS [6][7][8]. Accumulating evidence suggests that heterozygous ACAN mutations account for a certain percentage of autosomal dominant ISS.…”

The skeletal dysplasias

“…This novel skeletal disorder, SEMD Aggrecan type results from homozygosity for a missense mutation, asp2267-to-asn (D2267N) in the C-type lectin domain within the G3 domain of the molecule. 95 …”