Italian cohort of Lafora disease: Clinical features, disease evolution, and genotype-phenotype correlations

Abstract

Background: Lafora disease (LD) is characterized by progressive myoclonus, refractory epilepsy, and cognitive deterioration. This complex neurodegenerative condition is caused by pathogenic variants in EPM2A/EPM2B genes, encoding two essential glycogen metabolism enzymes known as laforin and malin. Long-term follow-up data are lacking. We describe the clinical features and genetic findings of a cohort of 26 Italian patients with a long clinical follow-up.

Methods: Patients with EPM2A/EPM2B pathogenic variants were identified by direct gene sequencing or gene panels with targeted re-sequencing. Disease progression, motor functions, and mental performance were assessed by a simplified disability scale. Spontaneous/action myoclonus severity was scored by the Magaudda Scale.

Results: Age range was 12.2-46.2 years (mean:25.53 ± 9.14). Age at disease onset ranged from 10 to 22 years (mean:14.04 ± 2.62). The mean follow-up period was 11.48 ± 7.8 years. Twelve out of the 26 (46%) patients preserved walking ability and 13 (50%) maintained speech. A slower disease progression with preserved ambulation and speech after ≥4 years of follow-up was observed in 1 (11%) out of the 9 (35%) EPM2A patients and in 6 (35%) out of the 17 (65%) EPM2B patients. Follow-up was >10 years in 7 (41.2%) EPM2B individuals, including two harbouring the homozygous p.(D146N) pathogenic variant.

Conclusions: This study supports an overall worse disease outcome with severe deterioration of ambulation and speech in patients carrying EPM2A mutations. However, the delayed onset of disabling symptoms observed in the EPM2B subjects harbouring the p.(D146N) pathogenic variant suggests that the underlying causative variant may still influence LD severity.

Keywords: EPM2A; EPM2B; Epilepsy; Lafora disease; Neurodegeneration; Progressive myoclonus.

Fig. 1.

Correlation between age at disease onset and spontaneous or action myoclonus severities.

Fig. 2.

LD causing mutations in our cohort and that of 2006. A) Laforin. CBD, carbohydrate-binding domain; DSP, dual-specificity phosphatase. B) Malin. RING, E2 interacting domain; NHL, protein interaction domain. The six NHL repeats are typical of E2 ubiquitin ligases [13]. Recurrent mutations are marked with a “star”.

Fig. 3.

Correlation between onset ages and walking capability in EPM2B patients.

Fig. 4.

Relationship between disease severity and disease duration in the EPM2A and EPM2B patients. Legend: r_S = Spearman’s correlation coefficient; n = number.