INCORPORATION OF STRUCTURALLY DEFECTIVE TYPE-II COLLAGEN INTO CARTILAGE MATRIX IN KNIEST CHONDRODYSPLASIA

Kniest dysplasia, a human chondrodysplasia that severely affects skele tal growth, is caused by mutations in the type II collagen gene, COL2A 1. We report here on abnormal type II collagen in the cartilage from a lethal Kniest dysplasia case and identify a novel exon-skipping mutat ion. Screening of cyanogen bromide (CB) peptides from the cartilage sa mples by SDS-PAGE indicated an abnormality in peptide alpha 1(II)CB11. Further peptide mapping and N-terminal sequence analysis showed a 15- amino-acid deletion encoded by exon 15 in about 25% of the alpha 1(II) chains in the cartilage. The mutation responsible for exon skipping w as found by sequencing amplified genomic DNA. The baby was heterozygou s for a G to A transition at the first position of the splice donor of intron 15. Pepsin-solubilized type II collagen from the cartilage mat rix contained both normal alpha 1(II) and shortened chains expressed f rom the mutant allele. Trypsin cleaved the native molecules below 37 d egrees C selectively at a site within the exon 15-encoded domain of th e normal alpha 1(II) chains. This is best explained by the coassembly of normal and truncated alpha 1(II) chains into heterotrimers in which the triple helix is normally folded in both directions from the delet ion site but the latter presents a region of local disruption. The fin dings support an emerging pattern of COL2A1 mutations that can cause K niest dysplasia. Short deletions (single or partial exon) clustered in one region of the alpha 1(II) chain are favored, resulting in abnorma l heterotrimeric molecules that become a significant component of the cartilage extracellular matrix. (C) 1998 Academic Press.