PREDOMINANCE OF THE RECURRENT MUTATION R635X IN THE LAMB3 GENE IN EUROPEAN PATIENTS WITH HERLITZ JUNCTIONAL EPIDERMOLYSIS-BULLOSA HAS IMPLICATIONS FOR MUTATION DETECTION STRATEGY

Junctional forms of epidermolysis bullosa (JEB) are characterized by t issue separation at the level of the lamina lucida, We have recently d isclosed specific mutations in the LAMA3, LAMB3, and LAMC2 genes encod ing the subunit polypeptides of the anchoring filament protein laminin 5 in 66 families with different variants of JEB, Examination of the J EB mutation database revealed recurrence of a particular C-->T substit ution at nucleotide position 1903 (exon 14) of LAMB3, resulting in the mutation R635X. The inheritance of this nonsense mutation was noted o n different genetic backgrounds, suggesting that R635X is a hotspot mu tation, In this study, we have performed mutation evaluation in a Euro pean cohort of 14 families with the lethal, Herlitz type of JEB (H-JEB ), The families were first screened for the presence of the R635X muta tion by restriction enzyme digestion of the PCR product corresponding to exon 14. Four of the probands were found to be homozygous and six w ere heterozygous for R635X. The remaining alleles were subjected to mu tation screening by PCR amplification of individual exons of LAMB3 and LAMC2, followed by heteroduplex analysis and nucleotide sequencing, I n three families (six alleles), mutations in LAMC2 were disclosed, In the remaining eight alleles, additional pathogenetic LAMB3 mutations w ere found, None of the patients had LAMA3 mutation, Thus, LAMB3 mutati ons accounted for 22 of 28 JEB alleles (79%), and a total of 14 of 22 LAMB3 alleles (64%) harbored the R635X mutation, signifying its preval ence as a predominant genetic lesion underlying H-JEB in this European cohort of patients, This recurrent mutation will facilitate screening of additional JEB patients for the purpose of prenatal testing of fet uses at risk for recurrence.