EXPRESSION, IN CARTILAGE, OF A 7-AMINO-ACID DELETION IN TYPE-II COLLAGEN FROM 2 UNRELATED INDIVIDUALS WITH KNIEST-DYSPLASIA

Kniest dysplasia is a heritable chondrodysplasia that severely affects skeletal growth. Recent evidence suggests that the etiology is based on mutations in COL2A1, the gene for collagen type II. We report the d etection and partial characterization of an identical defect in type I I collagen in two unrelated patients with Kniest dysplasia. Analysis o f cyanogen bromide (CB)-digested cartilage samples from both probands by SDS-PAGE revealed an abnormal band for peptide alpha 1(II)CB12. The peptide was purified and digested with endoproteinase Asp-N. Fragment s unique to the Kniest tissues were identified by reverse-phase high-p ressure liquid chromatography and by sequence analysis. The results es tablished a deletion of amino acids 102-108 of the alpha 1(II) triple- helical domain, which disrupted the (gly-X-Y)n repeat needed for helix formation. This was confirmed by sequence analysis of DNA amplified f rom both probands, revealing the molecular basis to be a single nucleo tide mutation at a CpG dinucleotide (GCG-->GTG) in the codon for alani ne 102. The mutation created a new splice donor site, which would acco unt for the absence of the last seven amino acids from the 3' end of e xon 12 in alpha 1(ll)CB12. Light and electron micrographs of the proba nds' cartilage showed the perilacunar foamy matrix (''Swiss cheese'') characteristic of Kniest dysplasia and chondrocytes containing dilated rough endoplasmic reticulum, which earlier studies had shown were fil led with type II procollagen. These two cases strengthen the concept t hat Kniest dysplasia is based on mutations of COL2A1 and belongs withi n the broad spectrum of chondrodysplasias caused by type II collagenop athies.