Order of Intron Removal Influences Multiple Splice Outcomes, Including a Two-Exon Skip, in a COL5A1 Acceptor-Site Mutation That Results in Abnormal Pro-α1(V) N-Propeptides and Ehlers-Danlos Syndrome Type I

• Published in: American journal of human genetics Vol. 71; no. 3; pp. 451 - 465
• Main Authors: Takahara, Kazuhiko, Schwarze, Ulrike, Imamura, Yasutada, Hoffman, Guy G., Toriello, Helga, Smith, Lynne T., Byers, Peter H., Greenspan, Daniel S.
• Format: Journal Article
• Language: English
• Published: Chicago, IL Elsevier Inc 2002; University of Chicago Press; The American Society of Human Genetics
• Subjects: Biological and medical sciences; Medical sciences; Sarcoidosis. Granulomatous diseases of unproved etiology. Connective tissue diseases. Elastic tissue diseases. Vasculitis; Human; Skin disease; Elastic tissue disease; Transcription; Pathogenesis; Diseases of the osteoarticular system; Clinical form; Genetic determinism; Genetic disease; Case study; Gene; Intron; Collagen; Ehlers Danlos syndrome; Systemic disease; Mutation
• ISSN: 0002-9297; 1537-6605
• DOI: 10.1086/342099

Ehlers-Danlos syndrome (EDS) type I (the classical variety) is a dominantly inherited, genetically heterogeneous connective-tissue disorder. Mutations in the COL5A1 and COL5A2 genes, which encode type V collagen, have been identified in several individuals. Most mutations affect either the triple-helical domain of the protein or the expression of one COL5A1 allele. We identified a novel splice-acceptor mutation (IVS4-2A→G) in the N-propeptide-encoding region of COL5A1, in one patient with EDS type I. The outcome of this mutation was complex: In the major product, both exons 5 and 6 were skipped; other products included a small amount in which only exon 5 was skipped and an even smaller amount in which cryptic acceptor sites within exon 5 were used. All products were in frame. Pro-α1(V) chains with abnormal N-propeptides were secreted and were incorporated into extracellular matrix, and the mutation resulted in dramatic alterations in collagen fibril structure. The two-exon skip occurred in transcripts in which intron 5 was removed rapidly relative to introns 4 and 6, leaving a large (270 nt) composite exon that can be skipped in its entirety. The transcripts in which only exon 5 was skipped were derived from those in which intron 6 was removed prior to intron 5. The use of cryptic acceptor sites in exon 5 occurred in transcripts in which intron 4 was removed subsequent to introns 5 and 6. These findings suggest that the order of intron removal plays an important role in the outcome of splice-site mutations and provide a model that explains why multiple products derive from a mutation at a single splice site.