SPLICING DEFECTS IN THE COL3A1 GENE - MARKED PREFERENCE FOR 5'-(DONOR) SPLICE-SITE MUTATIONS IN PATIENTS WITH EXON-SKIPPING MUTATIONS AND EHLERS-DANLOS-SYNDROME TYPE-IV

Ehlers-Danlos syndrome (EDS) type IV results from mutations in the COL 3A1 gene, which encodes the constituent chains of type III procollagen . We have identified, in 33 unrelated individuals or families with EDS type IV, mutations that affect splicing, of which 30 are point mutati ons at splice junctions and 3 are small deletions that remove splice-j unction sequences and partial exon sequences. Except for one point mut ation at a donor site, which ileads to partial intron inclusion, and a single base-pair substitution at an acceptor site, which gives rise t o inclusion of the complete upstream intron into the mature mRNA, all mutations result in deletion of a single exon as the only splice alter ation. Of the exonskipping mutations that are due to single base subst itutions, which we have identified in 28 separate individuals, only tw o affect the splice-acceptor site. The underrepresentation of splice a cceptor-site mutations suggests that the favored consequence of 31 mut ations is the use of an alternative acceptor site that creates a null allele with a premature-termination codon. The phenotypes of those mut ations may differ, with respect to either their severity or their symp tomatic range, from the usual presentation of EDS type IV and thus hav e been excluded from analysis.