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. 2002 May 15;11(11):1263-71.
doi: 10.1093/hmg/11.11.1263.

Genotype-phenotype correlations for EPM2A mutations in Lafora's progressive myoclonus epilepsy: exon 1 mutations associate with an early-onset cognitive deficit subphenotype

Subramaniam Ganesh  1 , Antonio V Delgado-Escueta, Toshimitsu Suzuki, Silvana Francheschetti, Concetta Riggio, Giuiliano Avanzini, Adrian Rabinowicz, Saeed Bohlega, Julia Bailey, Maria E Alonso, Astrid Rasmussen, Alfredo E Thomson, Adriana Ochoa, Aurelio J Prado, Marco T Medina, Kazuhiro Yamakawa
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Genotype-phenotype correlations for EPM2A mutations in Lafora's progressive myoclonus epilepsy: exon 1 mutations associate with an early-onset cognitive deficit subphenotype

Subramaniam Ganesh et al. Hum Mol Genet. .

Abstract

Mutations in the EPM2A gene encoding a dual-specificity phosphatase (laforin) cause an autosomal recessive fatal disorder called Lafora's disease (LD) classically described as an adolescent-onset stimulus-sensitive myoclonus, epilepsy and neurologic deterioration. Here we related mutations in EPM2A with phenotypes of 22 patients (14 families) and identified two subsyndromes: (i) classical LD with adolescent-onset stimulus-sensitive grand mal, absence and myoclonic seizures followed by dementia and neurologic deterioration, and associated mainly with mutations in exon 4 (P = 0.0007); (ii) atypical LD with childhood-onset dyslexia and learning disorder followed by epilepsy and neurologic deterioration, and associated mainly with mutations in exon 1 (P = 0.0015). To understand the two subsyndromes better, we investigated the effect of five missense mutations in the carbohydrate-binding domain (CBD-4; coded by exon 1) and three missense mutations in the dual phosphatase domain (DSPD; coded by exons 3 and 4) on laforin's intracellular localization in HeLa cells. Expression of three mutant proteins (T194I, G279S and Y294N) in DSPD formed ubiquitin-positive cytoplasmic aggregates, suggesting that they were folding mutants set for degradation. In contrast, none of the three CBD-4 mutants showed cytoplasmic clumping. However, CBD-4 mutants W32G and R108C targeted both cytoplasm and nucleus, suggesting that laforin had diminished its usual affinity for polysomes. Our data, thus, represent the first report of a novel childhood syndrome for LD. Our results also provide clues for distinct roles for the CBD-4 and DSP domains of laforin in the etiology of two subsyndromes of LD.

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