Leonarda Ianzano

Mutations in NHLRC1 cause progressive myoclonus epilepsy

Lafora progressive myoclonus epilepsy is characterized by pathognomonic endoplasmic reticulum (ER)-associated polyglucosan accumulations. We previously discovered that mutations in EPM2A cause Lafora disease. Here, we identify a second gene associated with this disease, NHLRC1 (also called EPM2B), which encodes malin, a putative E3 ubiquitin ligase with a RING finger domain and six NHL motifs. Laforin and malin colocalize to the ER, suggesting they operate in a related pathway protecting against polyglucosan accumulation and epilepsy.

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

Background: Lafora’s disease is a progressive myoclonus epilepsy with pathognomonic inclusions (polyglucosan bodies) caused by mutations in the EPM2A gene. EPM2A codes for laforin, a protein with unknown function. Mutations have 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 of this exon in Lafora’s disease. 2) To generate hypotheses about the biological function of laforin based on bioinformatic analyses. Methods: 1) PCR conditions and components were refined to allow amplification and sequencing of the first exon of EPM2A. 2) Extensive bioinformatic analyses of the primary structure of laforin were completed. Results: 1) Seven new mutations were identified in the putative exon 1. 2) Laforin is predicted not to localize to the cell membrane or any of the organelles. It contains all components of the catalytic active site of the family of dual-specificity phosphatases. It contains a sequence predicted to encode a carbohydrate binding domain (coded by exon 1) and two putative glucohydrolase catalytic sites. Conclusions: The identification of mutations in exon 1 of EPM2A establishes its role in the pathogenesis of Lafora’s disease. The presence of potential carbohydrate binding and cleaving domains suggest a role for laforin in the prevention of accumulation of polyglucosans in healthy neurons.

Laforin is a cell membrane and endoplasmic reticulum-associated protein tyrosine phosphatase

Lafora disease (LD) is the only progressive myoclonus epilepsy with polyglucosan bodies. Among conditions with polyglucosan bodies, LD is unique for the subcellular location of its polyglucosans in neuronal perikarya and dendrites and not in axons. Here we report that the protein encoded by the EPM2A gene, which is mutated in LD, localizes at the plasma membrane and the endoplasmic reticulum and that it is a functional protein tyrosine phosphatase. The significance of these findings in the epilepsy of LD and in the origin and characteristic subcellular location of Lafora bodies is discussed. Ann Neurol 2001;49:271–275

Clinical and genetic findings in 26 Italian patients with Lafora disease.

Summary:  Purpose: EPM2B mutations have been found in a variable proportion of patients with Lafora disease (LD). Genotype–phenotype correlations suggested that EPM2B patients show a slower course of the disease, with delayed age at death, compared with EPM2A patients. We herein report clinical and genetic findings of 26 Italian LD patients.

Identification of new and common mutations in the EPM2A gene in Lafora disease

Article abstract Lafora disease is a teenage onset progressive myoclonus epilepsy caused by mutations in the EPM2A gene. In this report, we describe new mutations within EPM2A, review the known mutations to date to identify the most common, and describe three simple tests for prenatal and carrier screening.

Genetic diagnosis in Lafora disease: genotype-phenotype correlations and diagnostic pitfalls.

Lafora disease (LD) can be diagnosed by skin biopsy, but this approach has both false negatives and false positives. Biopsies of other organs can also be diagnostic but are more invasive. Genetic diagnosis is also possible but can be inconclusive, for example, in patients with only one heterozygous EPM2A mutation and patients with apparently homozygous EPM2B mutations where one parent is not a carrier of the mutation. We sought to identify occult mutations and clarify the genotypes and confirm the diagnosis of LD in patients with apparent nonrecessive disease inheritance. We used single nucleotide polymorphism, quantitative PCR, and fluorescent in situ hybridization analyses. We identified large EPM2A and EPM2B deletions undetectable by PCR in the heterozygous state and describe simple methods for their routine detection. We report a coding sequence change in several patients and describe why the pathogenic role of this change remains unclear. We confirm that adult-onset LD is due to EPM2B mutations. Finally, we report major intrafamilial heterogeneity in age at onset in LD.