IDENTIFICATION OF 2 SPLICING MUTATIONS IN THE COLLAGEN TYPE-VII GENE (COL7A1) OF A PATIENT AFFECTED BY THE LOCALISATA VARIANT OF RECESSIVE DYSTROPHIC EPIDERMOLYSIS-BULLOSA

Collagen type VII gene (COL7A1) has been demonstrated to be altered in several variants of dystrophic epidermolysis bullosa (DEB), with eith er recessive or dominant mode of inheritance. We have identified two m utations in a patient affected by a localisata variant of recessive DE B (L-RDEB), which is characterized by the less severe phenotype of the syndrome. These mutations are the first splicing mutations so far des cribed for COL7A1 in DEB. One mutation is a paternally inherited A-->G transition at position -2 of the donor splicing site of intron 3, whi ch results in three aberrant mRNAs, depending on the skipping of exon 3, the usage of a cryptic donor site inside exon 3, or the maintenance of intron 3. The second mutation is a maternally inherited G-->A tran sition at position -1 of the donor splicing site of intron 95, which i nduces the activation of a cryptic donor site 7 nt upstream the normal site and gives rise to a deleted mRNA, in addition to the normal one. All aberrant mRNAs show a shift of the reading frame, thus generating premature termination codons of translation. Allele-specific analysis of the transcripts has shown that the maternal mutation does nor comp letely abolish the correct splicing of COLVII pre-mRNA, thus allowing, in the patient, the synthesis of a certain lever of a functional prot ein. This result is compatible with the mild clinical L-RDEB phenotype observed in our patient.