Dominant mutations in the type II collagen gene, COL2A1, produce spondyloepimetaphyseal dysplasia, Strudwick type.

The chondrodysplasias are a heterogeneous group of disorders characterized by abnormal growth or development of cartilage. Current classification is based on mode of inheritance as well as clinical, histologic, and/or radiographic features. A clinical spectrum of chondrodysplasia phenotypes, ranging from mild to perinatal lethal, is due to defects in the gene for type II collagen, COL2A1. This spectrum includes Stickler syndrome, Kniest dysplasia, spondyloepiphyseal dysplasia congenita (SEDC), achondrogenesis type II, and hypochondrogenesis. Individuals affected with these disorders exhibit abnormalities of the growth plate, nucleus pulposus, and vitreous humor, which are tissues that contain type II collagen. The Strudwick type of spondyloepimetaphyseal dysplasia (SEMD) is characterized by disproportionate short stature, pectus carinatum, and scoliosis, as well as dappled metaphyses (which are not seen in SEDC). The phenotype was first described by Murdoch and Walker in 1969, and a series of 14 patients was later reported by Anderson et al. The observation of two affected sibs born to unaffected parents led to the classification of SEMD Strudwick as an autosomal recessive disorder. We now describe the biochemical characterization of defects in alpha 1(II) collagen in three unrelated individuals with SEMD Strudwick, each of which is due to heterozygosity for a unique mutation in COL2A1. Our data support the hypothesis that some cases, if not all cases, of this distinctive chondrodysplasia result from dominant mutations in COL2A1, thus expanding the clinical spectrum of phenotypes associated with this gene.

Linkage mapping of the gene for type III collagen (COL3A1) to human chromosome 2q using a VNTR polymorphism.

The gene for the alpha 1 (III) chain of type III collagen, COL3A1, has been previously mapped to human chromosome 2q24.3-q31 by in situ hybridization. Physical mapping by pulsed-field gel electrophoresis has demonstrated that COL3A1 lies within 35 kb of COL5A2. We genotyped the CEPH families at the COL3A1 locus using a pentanucleotide repeat polymorphism within intron 25. We demonstrated significant linkage to 18 anonymous markers as well as the gene for carbamyl phosphate synthetase (CPSI), which we have previously mapped to this region. No recombination was seen between COL3A1 and COL5A2 (Z = 9.93 at theta = 0) or D2S24 (Z = 10.55 at theta = 0). The locus order is (D2S32-D2S138-D2S148)--(D2S24-COL5A2-CO L3A1)--(D2S118-D2S161), with odds of 1:2300 for the next most likely order. These relationships are consistent with the physical mapping of COL3A1 to the distal portion of 2q and place it proximal to CPSI by means of multipoint analysis. These linkage relationships should prove useful in further studies of Ehlers-Danlos syndrome type IV and carbamyl phosphate synthetase I deficiency and provide an additional framework for localizing other genes in this region.

Physical and linkage mapping of the human and murine genes for the alpha 1 chain of type IX collagen (COL9A1).

Type IX collagen, a member of the FACIT family of extracellular matrix proteins, is a heterotrimer composed of three genetically distinct alpha chains. The cDNAs for the human and mouse alpha 1 (IX) chains have been cloned. In this paper we confirm the mapping of the human COL9A1 gene to chromosome 6q12-q13 by fluorescence in situ hybridization utilizing two genomic clones which also contain short tandem repeat polymorphisms. We also report the characterization of these repeats and their incorporation into the chromosome 6 linkage map. The COL9A1 locus shows no recombination with the marker D6Z1 (Z = 27.61 at theta = O) and identifies the most likely locus order of KRAS1P-[D6Z1-COL9A1]-D6S30. In addition, using an interspecific backcross panel, we have mapped murine Col9a1 to mouse chromosome 1. Together with other comparative mapping results, these data suggest that the pericentric region of human chromosome 6 is homologous to the most proximal segment of mouse chromosome 1. These data may facilitate linkage studies with COL9A1 (or Col9a1) as a candidate gene for hereditary chondrodysplasias and osteoarthritis.

An RNA-splicing mutation (G+5IVS20) in the type II collagen gene (COL2A1) in a family with spondyloepiphyseal dysplasia congenita.

Defects in type II collagen have been demonstrated in a phenotypic continuum of chondrodysplasias that includes achondrogenesis II, hypochondrogenesis, spondyloepiphyseal dysplasia congenita (SEDC), Kniest dysplasia, and Stickler syndrome. We have determined that cartilage from a terminated fetus with an inherited form of SEDC contained both normal alpha 1(II) collagen chains and chains that lacked amino acids 256-273 of the triple-helical domain. PCR amplification of this region of COL2A1, from genomic DNA, yielded products of normal size, while amplification of cDNA yielded a normal sized species and a shorter fragment missing exon 20. Sequence analysis of genomic DNA from the fetus revealed a G-->T transversion at position +5 of intron 20; the affected father was also heterozygous for the mutation. Allele-specific PCR and heteroduplex analysis of a VNTR in COL2A1 independently confirmed the unaffected status of a fetus in a subsequent pregnancy. Thermodynamic calculations suggest that the mutation prevents normal splicing of exon 20 by interfering with binding of U1 small-nuclear RNA to pre-mRNA, thus leading to skipping of exon 20 in transcripts from the mutant allele. Electron micrographs of diseased cartilage showed intracellular inclusion bodies, which were stained by an antibody to alpha 1(II) procollagen. Our findings support the hypothesis that alpha-chain length alterations that preserve the Gly-X-Y repeat motif of the triple helix result in partial intracellular retention of alpha 1(II) procollagen and produce mild to moderate chondrodysplasia phenotypes.