Stover M L, Primorac D, Liu S C, McKinstry M B, Rowe D W
Department of Pediatrics, University of Connecticut Health Center, Farmington 06030.
J Clin Invest. 1993 Oct;92(4):1994-2002. doi: 10.1172/JCI116794.
Osteogenesis imperfecta (OI) type I is the mildest form of heritable bone fragility resulting from mutations within the COL1A1 gene. We studied fibroblasts established from a child with OI type I and demonstrated underproduction of alpha 1 (I) collagen chains and alpha 1 (I) mRNA. Indirect RNase protection suggested two species of alpha 1 (I) mRNA, one of which was not collinear with fully spliced alpha 1 (I) mRNA. The noncollinear population was confined to the nuclear compartment of the cell, and contained the entire sequence of intron 26 and a G-->A transition in the first position of the intron donor site. The G-->A transition was also identified in the genomic DNA. The retained intron contained an in-frame stop codon and introduced an out-of-frame insertion within the collagen mRNA producing stop codons downstream of the insertion. These changes probably account for the failure of the mutant RNA to appear in the cytoplasm. Unlike other splice site mutations within collagen mRNA that resulted in exon skipping and a truncated but inframe RNA transcript, this mutation did not result in production of a defective collagen pro alpha 1 (I) chain. Instead, the mild nature of the disease in this case reflects failure to process the defective mRNA and thus the absence of a protein product from the mutant allele.
I型成骨不全症（OI）是由COL1A1基因突变导致的遗传性骨脆性最轻微的一种形式。我们研究了从一名I型OI患儿身上建立的成纤维细胞，结果表明α1（I）胶原链和α1（I）mRNA产量不足。间接核糖核酸酶保护实验提示存在两种α1（I）mRNA，其中一种与完全剪接的α1（I）mRNA不共线。不共线的群体局限于细胞核内，包含内含子26的完整序列以及内含子供体位点第一位的G→A转换。在基因组DNA中也鉴定到了G→A转换。保留的内含子包含一个框内终止密码子，并在胶原mRNA内引入了一个框外插入，在插入位点下游产生终止密码子。这些变化可能解释了突变RNA未能出现在细胞质中的原因。与胶原mRNA内导致外显子跳跃和截短但框内RNA转录本的其他剪接位点突变不同，这种突变并未导致产生有缺陷的胶原原α1（I）链。相反，该病例中疾病的轻微性质反映了无法处理有缺陷的mRNA，因此突变等位基因没有蛋白质产物。
