Genetic heterogeneity of cutis laxa: a heterozygous tandem duplication within the fibulin-5 (FBLN5) gene.
Inherited cutis laxa is a connective tissue disorder characterized by loose skin and variable internal organ involvement, resulting from paucity of elastic fibers. Elsewhere, frameshift mutations in the elastin gene have been reported in three families with autosomal dominant inheritance, and a family with autosomal recessive cutis laxa was recently reported to have a homozygous missense mutation in the fibulin-5 gene. In the present study, we analyzed the gene expression of elastin and fibulins 1-5 in fibroblasts from five patients with cutis laxa. One patient was found to express both normal (2.2 kb) and mutant (2.7 kb) fibulin-5 mRNA transcripts. The larger transcript contains an internal duplication of 483 nucleotides, which resulted in the synthesis and secretion of a mutant fibulin-5 protein with four additional tandem calcium-binding epidermal growth factor-like motifs. The mutation arose from a 22-kb tandem gene duplication, encompassing the sequence from intron 4 to exon 9. No fibulin-5 or elastin mutations were detected in the other patients. The results demonstrate that a heterozygous mutation in fibulin-5 can cause cutis laxa and also suggest that fibulin-5 and elastin gene mutations are not the exclusive cause of the disease.
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