LOSS OF PLECTIN CAUSES EPIDERMOLYSIS-BULLOSA WITH MUSCULAR-DYSTROPHY - CDNA CLONING AND GENOMIC ORGANIZATION

Plectin is a widely expressed high molecular weight protein that is in volved in cytoskeleton-membrane attachment in epithelial cells, muscle , and other tissues. The human autosomal recessive disorder epidermoly sis bullosa with muscular dystrophy (MD-EBS) shows epidermal blister f ormation at the level of the hemidesmosome and is associated with a my opathy of unknown etiology. Here, plectin was found to be absent in sk in and cultured keratinocytes from an MD-EBS patient by immunofluoresc ence and immunoprecipitation, suggesting that plectin is a candidate g ene/protein system for MD-EBS mutation. The 14800-bp human plectin cDN A was cloned and sequenced. The predicted 518-kD polypeptide has homol ogy to the actin-binding domain of the dystrophin family at the amino terminus, a central rod domain, and homology to the intermediate filam ent-associated protein desmoplakin at the carboxyl terminus. The corre sponding human gene (PLEC1), consisting of 33 exons spanning >26 kb of genomic DNA was cloned, sequenced, and mapped to chromosomal band 8q2 4. Homozygosity by descent was observed in the consanguineous MD-EBS f amily with intragenic plectin polymorphisms. Direct sequencing of PCR- amplified plectin cDNA from the patient's keratinocytes revealed a hom ozygous 8-bp deletion in exon 32 causing a frameshift and a premature termination codon 42 bp downstream. The clinically unaffected parents of the proband were found to be heterozygous carriers of the mutation. These results establish the molecular basis of MD-EBS in this family and clearly demonstrate the important structural role for plectin in c ytoskeleton-membrane adherence in both skin and muscle.