Multiexon deletion in an osteogenesis imperfecta variant with increased type III collagen mRNA

Recently, the dermal fibroblasts (ATCC CRL 1262) of a lethal perinatal variant of osteogenesis imperfecta have been used for the first molecular characterization of a collagen gene defect (Chu, M.L., Williams, C.J., Pepe, G., Hirsch, J.L., Prockop, D.J., and Ramirez, F. (1983) Nature (Lond.) 304, 78-80). These studies revealed that the patient was heterozygous for an internal deletion of approximately 500 base pairs in the pro-α1(I) collagen gene, consistent with previous investigations indicating that CRL 1262 fibroblasts equally synthesized a normal and a shortened pro-α1(I) chain (Barsh, G.S., and Byers, P.H. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 5142-5146). Cloning and analysis of the affected allele of CRL 1262 has now indicated that the deletion is contained between two introns of the pro-α1(I) gene and results in the elimination of three exons of the triple helical domain. Furthermore, the termini of the rearrangement are located within two short inverted repeats suggesting that the self-complementary nature of these DNA elements may have favored the formation of a DNA secondary structure intermediate which, in turn, served as substrate for the deletion. Evidence are also presented for an elevated Type III collagen mRNA content in the patient fibroblasts.