Aberrant splicing of the type III procollagen mRNA leads to intracellular degradation of the protein in a patient with ehlers‐danlos type IV

Ehlers‐Danlos syndrome type IV (EDS IV) is an autosomal dominant disorder characterized by fragile skin, blood vessels, and internal organs and associated with decreased production, secretion, or thermal stability of type III procollagen. Mutations in the gene for type III procollagen have been identified in patients exhibiting decreased secretion or thermal stability of the protein, but no defect has been elucidated to explain the decreased production of type III procollagen in some patients with EDS IV. We report on a patient with a moderate case of EDS IV who produced decreased amounts of type III procollagen despite normal levels of translatable type III procollagen mRNA. SI nuclease analysis of the type III procollagen mRNA indicated a defect in the region encoding exon 27. Sequence analysis of cDNA clones and genomic fragments generated by polymerase chpin reaction amplification revealed that sequences encoded by exon 27 were absent from 3 out of 5 cDNA clones and that a G at the +5 position of the splce donor site in intron 27 was changed to an A in one allcle of the patient's type III procollagen gene. Using a cDNA genomic DNA hybrid probe in Si nuclease analysis, fragments consistent with mRNA species containing and lacking exon 27 were detected in a 1:1 ratio. Pulse label and chase experiments in the presence or absenci: of brefeldin A indicated that most of the type III procollagen molecules synthesized by the patient'; fibroblasts were not secreted into the medium but were degraded in the endoplasmic reticulum‐Golgi compartment by a nonlysosomal mechanism. © 1995 Wiley‐Liss, Inc.