Brachydactyly type C caused by a homozygous missense mutation in the prodomain of CDMP1

Brachydactyly type C (BDC) is characterized by shortening of the middle phalanges of the index, middle, and little finger with hyperphalangy, usually of the index and middle finger. Heterozygous mutations of the cartilage derived morphogenetic protein-1 (CDMP1) resulting in a loss of function have been reported in BDC. We here describe a large kindred with a semi-dominant form of BDC and pronounced ulnar deviation of the second and third digits. In this family a novel homozygous missense mutation was identified (517A > G) changing methionine to valine at amino acid position 173. The mutation is located within a highly conserved seven amino acid region of the prodomain of CDMP1. Hand radiographs of heterozygous mutation carriers showed mild shortening of the metacarpals IV and V; a finding confirmed by the analysis of their metacarpophalangeal profiles (MCPPs). The mutation described here points toward an important function of the prodomain for the folding, secretion, and availability of biologically active CDMP1

Loss of chondroitin 6-O-sulfotransferase-1 function results in severe human chondrodysplasia with progressive spinal involvement

We studied two large consanguineous families from Oman with a distinct form of spondyloepiphyseal dysplasia (SED Omani type). By using a genome-wide linkage approach, we were able to map the underlying gene to a 4.5-centimorgan interval on chromosome 10q23. We sequenced candidate genes from the region and identified a missense mutation in the chondroitin 6-O-sulfotransferase (C6ST-1) gene (CHST3) changing an arginine into a glutamine (R304Q) in the well conserved 3′-phosphoadenosine 5′-phosphosulfate binding site. C6ST-1 catalyzes the modifying step of chondroitin sulfate (CS) synthesis by transferring sulfate to the C-6 position of the N-acetylgalactosamine of chondroitin. From the crystal structures of other sulfotransferases, it could be inferred that Arg-304 is essential for the structure of the cosubstrate binding site. We used recombinant C6ST-1 to show that the identified missense mutation completely abolishes C6ST-1 activity. Disaccharide composition analysis of CS chains by anion-exchange HPLC shows that both ΔHexA-GalNAc(6S) and ΔHexA(2S)-GalNAc(6S) were significantly reduced in the patient's cells and that ΔHexA-GalNAc(4S,6S), undetectable in controls, was elevated. Analysis of the patient's urine shows marked undersulfation of CS, in particular reduction in 6-O-sulfated disaccharide and an increase in the nonsulfated unit. Our results indicate that the mutation in CHST3 described here causes a specific but generalized defect of CS chain sulfation resulting in chondrodysplasia with major involvement of the spine

An inversion involving the mouse Shh locus results in brachydactyly through dysregulation of Shh expression

Short digits (Dsh) is a radiation-induced mouse mutant. Homozygous mice are characterized by multiple defects strongly resembling those resulting from Sonic hedgehog (Shh) inactivation. Heterozygous mice show a limb reduction phenotype with fusion and shortening of the proximal and middle phalanges in all digits, similar to human brachydactyly type A1, a condition caused by mutations in Indian hedgehog (IHH). We mapped Dsh to chromosome 5 in a region containing Shh and were able to demonstrate an inversion comprising 11.7 Mb. The distal breakpoint is 13.298 kb upstream of Shh, separating the coding sequence from several putative regulatory elements identified by interspecies comparison. The inversion results in almost complete downregulation of Shh expression during E9.5–E12.5, explaining the homozygous phenotype. At E13.5 and E14.5, however, Shh is upregulated in the phalangeal anlagen of Dsh/+ mice, at a time point and in a region where WT Shh is never expressed. The dysregulation of Shh expression causes the local upregulation of hedgehog target genes such as Gli1-3, patched, and Pthlh, as well as the downregulation of Ihh and Gdf5. This results in shortening of the digits through an arrest of chondrocyte differentiation and the disruption of joint development