Splice site mutation causing deletion of exon 21 sequences from the proα2(I) chain of type I collagen in a patient with severe dentinogenesis imperfecta but very mild osteogenesis imperfecta

✍ Scribed by Alan C. Nicholls; Jane Oliver; Seamus McCarron; Gerald B. Winter; F. Michael Pope

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 672 KB
• Volume: 7
• Category: Article
• ISSN: 1059-7794
• DOI: 10.1002/(sici)1098-1004(1996)7:3<219::aid-humu6>3.0.co;2-5

✦ Synopsis

Communicated by Alec J. Jefieys An eight-year-old boy was referred for dental assessment of dentinogenesis imperfecta, a full clinical examination also revealed joint hypermobility and some features of mild osteogenesis imperfecta although he had suffered few fractures. Analysis of the collagens produced by both gingival and skin fibroblast cultures showed the synthesis and intracellular retention of an abnormal a2(I) chain that migrated faster than normal on SDS-PAGE. Cyanogen bromide peptide mapping of this intracellular protein indicated a probable deletion in the N-terminal peptide a2CB4. The denaturation temperature of the mutant protein was only 36"C, some 6°C below normal. At 37°C secretion of abnormal protein was not detectable but at a lower temperature (30°C) some was secreted into the medium. RT-PCR amplification of mRNA coding for a2CB4 revealed a heterozygous deletion of the 108 bp exon 21 of COLlA2. Sequencing of PCR amplified genomic DNA identified a G+A transition in the moderately conserved + 5 position of the IVS 2 1 5' consensus splice site causing the skipping of exon 21.

Hybridization with allele-specific oligonucleotides showed no other family member had this base change. Since the cDNA deletion was associated with the (-) allele of a Pvu I1 polymorphism in exon 25 of COLlA2 we could demonstrate that the mutant pre-mRNA was alternatively spliced yielding both full length and deleted transcripts. Family genotype analysis indicated the mutation had originated in the paternal a2(I) gene. 8 19% WiIey-Liss, Inc.