Ehlers-Danlos syndrome type VII: a single base change that causes exon skipping in the type I collagen alpha 2(I)...

We have examined the procollagens and collagens produced by skin fibroblasts from a patient with Ehlers-Danlos syndrome type VII. The patient was heterozygous for an abnormal alpha 2(I) chain migrating with the approximate size of pN alpha 2(I) chains after pepsin digestion. Peptide mapping suggested that the abnormality was located at the amino-terminus of the alpha 2(I) chain. Quantitative analysis of the alpha 2(I) mRNA indicated loss of the exon 6 sequences, and subsequent polymerase chain reaction amplification of cDNA demonstrated a deletion of the 54 bp of exon 6 from some of the alpha 2(I) mRNA. Analysis of genomic DNA from the patient revealed a single base change in one COL1A2 allele, substituting an A for a G as the first base of intron 6. This change mutates the obligate GT-dinulceotide splicing signal to AT and leads to exon skipping with splicing from exon 5 to exon 7. Loss of exon 6 sequences results in the loss of the procollagen-N-propeptidase cleavage site and a lysine residue that normally participates in covalent intermolecular crosslinking within collagen fibres.