Mutation spectrum and predicted function of laforin in Lafora's progressive myoclonus epilepsy

Background: Lafora's disease is a progressive myoclonus epilepsy with patho gnomonic inclusions (polyglucosan bodies) caused by mutations in the EPM2A gene. EPM2A codes for laforin, a protein with unknown function. Mutations h ave been reported in the last three of the gene's exons, To date, the first exon has not been determined conclusively. It has been predicted based on genomic DNA sequence analysis including comparison with the mouse homologue . Objectives: 1) To detect new mutations in exon 1 and establish the role o f this exon in Lafora's disease. 2) To generate hypotheses about the biolog ical function of laforin based on bioinformatic analyses. Methods: 1) PCR c onditions and components were refined to allow amplification and sequencing of the first exon of EPM2A. 2) Extensive bioinformatic analyses of the pri mary structure of laforin were completed. Results: 1) Seven new mutations w ere identified in the putative exon 1. 2) Laforin is predicted not to local ize to the cell membrane or any of the organelles. If contains all componen ts of the catalytic active site of the family of dual-specificity phosphata ses. It contains a sequence predicted to encode a carbohydrate binding doma in (coded by exon 1) and two putative glucohydrolase catalytic sites. Concl usions: The identification of mutations in exon 1 of EPM2A establishes its role in the pathogenesis of Lafora's disease. The presence of potential car bohydrate binding and cleaving domains suggest a role for laforin in the pr evention of accumulation of polyglucosans in healthy neurons.