Gatalica B, Pulkkinen L, Li K, Kuokkanen K, Ryynänen M, McGrath J A, Uitto J
Department of Dermatology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107-5541, USA.
Am J Hum Genet. 1997 Feb;60(2):352-65.
Generalized atrophic benign epidermolysis bullosa (GABEB) is a nonlethal variant of junctional epidermolysis bullosa (JEB). Previous findings have suggested that type XVII collagen is the candidate gene for mutations in this disease. We now have cloned the entire human type XVII collagen gene (COL17A1) and have elucidated its intron-exon organization. The gene comprises 56 distinct exons, which span approximately 52 kb of the genome, on the long arm of chromosome 10. It encodes a polypeptide, the alpha1(XVII) chain, consisting of an intracellular globular domain, a transmembrane segment, and an extracellular domain that contains 15 separate collagenous subdomains, the largest consisting of 242 amino acids. We also have developed a strategy to identify mutations in COL17A1 by use of PCR amplification of genomic DNA, using primers placed on the flanking introns. The PCR products are scanned for sequence variants by heteroduplex analysis using conformation-sensitive gel electrophoresis and then are subjected to direct automated sequencing. We have identified several intragenic polymorphisms in COL17A1, as well as mutations, in both alleles, in two Finnish families with GABEB. The probands in both families showed negative immunofluorescence staining with an anti-type XVII collagen antibody. In one family, the proband was homozygous for a 5-bp deletion, 2944del5, which resulted in frameshift and a premature termination codon of translation. The proband in the other family was a compound heterozygote, with one allele containing the 2944del5 mutation and the other containing a nonsense mutation, Q1023X. These results expand the mutation database in different variants of JEB, and they attest to the functional importance of type XVII collagen as a transmembrane component of the hemidesmosomes at the dermal/epidermal junction.
泛发性萎缩性良性大疱性表皮松解症（GABEB）是交界性大疱性表皮松解症（JEB）的一种非致死性变体。先前的研究结果表明，ⅩⅦ型胶原是该疾病突变的候选基因。我们现已克隆了完整的人类ⅩⅦ型胶原基因（COL17A1），并阐明了其内含子-外显子结构。该基因由56个不同的外显子组成，跨越基因组约52kb，位于10号染色体长臂上。它编码一种多肽，即α1（ⅩⅦ）链，由一个细胞内球状结构域、一个跨膜区段和一个细胞外结构域组成，该细胞外结构域包含15个独立的胶原亚结构域，其中最大的由242个氨基酸组成。我们还开发了一种策略，通过使用位于侧翼内含子上的引物对基因组DNA进行PCR扩增来鉴定COL17A1中的突变。通过使用构象敏感凝胶电泳的异源双链分析扫描PCR产物中的序列变异，然后进行直接自动测序。我们在两个患有GABEB的芬兰家族中，在COL17A1基因的两个等位基因中都鉴定出了几个基因内多态性以及突变。两个家族中的先证者用抗ⅩⅦ型胶原抗体进行免疫荧光染色均呈阴性。在一个家族中，先证者为5bp缺失（2944del5）的纯合子，这导致了移码和翻译的提前终止密码子。另一个家族中的先证者是复合杂合子，一个等位基因含有2944del5突变，另一个含有无义突变Q1023X。这些结果扩展了JEB不同变体中的突变数据库，并且证明了ⅩⅦ型胶原作为真皮/表皮交界处半桥粒跨膜成分的功能重要性。
