A SINGLE AMINO-ACID SUBSTITUTION (G103D) IN THE TYPE-II COLLAGEN TRIPLE-HELIX PRODUCES KNIEST DYSPLASIA

Kniest dysplasia is a moderately severe chondrodysplasia phenotype tha t results from mutations in the gene for type II collagen, COL2A1. Cha racteristics of the disorder include a short trunk and extremities, mi d-face hypoplasia, cleft palate, myopia, retinal detachment, and heari ng loss. Recently, deletions of all or part of exon 12 have been ident ified in individuals with Kniest dysplasia, suggesting that mutations within this region of the protein may primarily result in the Kniest d ysplasia phenotype. We used SSCP to analyze an amplified genomic DNA f ragment containing exon 12 from seven individuals with Kniest dysplasi a. An abnormality was identified in one patient. DNA sequence analysis demonstrated that the patient was heterozygous for a G to A transitio n that implied substitution of glycine(103) of the triple helical doma in by aspartate. The mutation was not observed in DNA from either of t he clinically unaffected parents of the proband. Protein microsequenci ng demonstrated expression of the abnormal allele in cartilage. These data demonstrate that point mutations which result in single amino aci d substitutions can produce Kniest dysplasia and further support the h ypothesis that alteration of a domain, which includes the region encod ed by exon 12, in the type II collagen protein leads to this disorder.