Deletion of 19 base pairs in intron 13 of the gene for the pro alpha 2(I) chain of type-I procollagen (COL1A2) causes exon skipping in a proband with type-I osteogenesis imperfecta.
Skin fibroblasts from a proband with mild osteogenesis imperfecta (type I) synthesized normal pro alpha 2(I) chains and shortened pro alpha 2(I) chains of type-I procollagen. The type-I collagen that contained the shortened alpha 2(I) chains was thermally unstable in that it was cleaved at 30 degrees C by a mixture of trypsin and chymotrypsin. The mutation generating the shortened pro alpha 2(I) chains was shown to be a deletion of 19 base pairs from +4 to +22 of intron 13 of the COL1A2 gene by sequencing of genomic DNA and allele-specific oligonucleotide hybridization. The same mutation was found in the proband's affected father. Probe-protection experiments with S1 nuclease demonstrated that about 88% of the RNA transcripts from the mutated allele were spliced by exon skipping from exon 12 to exon 14 and that about 12% of the RNA transcripts were normally spliced. There was no evidence for use of cryptic splice sites, even though two cryptic splice sites had more favorable statistical scores and delta G degree 37 values than the new site that was created by the mutation and that was used for splicing of 12% of the transcripts into a normal mRNA. Comparison of the results with observations on 17 previously reported mutations that produced in-frame deletions of amino acids from the triple-helical domain of type-I collagen indicated that deletions in the N-terminal half of the alpha 2(I) chain tended to produce milder phenotypes than similar deletions elsewhere in the alpha 1(I) or alpha 2(I) chains.
Zhuang
J
J
Department of Biochemistry and Molecular Biology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107.
Tromp
G
G
Kuivaniemi
H
H
Nakayasu
K
K
Prockop
D J
DJ
D000293:Adolescent; D001482:Base Composition; D001483:Base Sequence; D002478:Cells, Cultured; D004247:DNA; D005091:Exons; D005260:Female; D006801:Humans; D007438:Introns; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D010013:Osteogenesis Imperfecta / Q000235:genetics*; D011347:Procollagen / Q000235:genetics*; D012326:RNA Splicing; D017384:Sequence Deletion
D011347:Procollagen; D004247:DNA