CHARACTERIZATION OF AN ARGININE-789 TO CYSTEINE SUBSTITUTION IN ALPHA-1(II) COLLAGEN CHAINS OF A PATIENT WITH SPONDYLOEPIPHYSEAL DYSPLASIA

A child with spondyloepiphyseal dysplasia congenita was shown to be he terozygous for a mutation of the COL2A1 gene that encodes the alpha1(I I) chain of type II collagen. The alpha1(II) chains extracted from car tilage contained disulfide-bonded dimeric and trimeric alpha1(II) chai ns. Carboxymethylation confirmed that some of the type II collagen cha ins contained cysteine residues that are not normally present in alpha 1(II) chains. Cyanogen bromide peptide mapping showed that the abnorma l cysteine residue was located in the alpha1(II) CB10.5 peptide. Ampli fication products of the corresponding region of alpha1(II) cDNA prepa red from cultured dermal fibroblasts were shown by chemical cleavage a nd single strand conformation polymorphism analyses to contain a seque nce anomaly. DNA sequencing showed a transition of C2913T in exon 41 o f one allele of the COL2A1 gene resulting in the substitution of argin ine 789 by cysteine in the alpha1(II) chain. The mutation resulted in the loss of a MaeII cleavage site that was used to confirm that the pr oband was heterozygous for the mutation and that neither parent showed evidence of the mutation. The type II collagen extracted from cartila ge and from chondrocytes cultured in alginate beads showed similar cha racteristics. Approximately a third of the type II collagen chains wer e mutant, and the secretion of molecules containing mutant chains was impaired. The thermal stability of the collagen extracted from cartila ge was normal. This study confirmed the importance of dominant negativ e mutations of the COL2A1 gene in producing the spondyloepiphyseal dys plasia congenita phenotype.