EHLERS-DANLOS SYNDROME TYPE-VII - A SINGLE BASE CHANGE THAT CAUSES EXON SKIPPING IN THE TYPE-I COLLAGEN ALPHA-2(I) CHAIN

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.