An empirical pipeline for personalized diagnosis of Lafora disease mutations

Abstract

Summary Lafora disease (LD) is a fatal childhood dementia characterized by progressive myoclonic epilepsy manifesting in the teenage years, rapid neurological decline, and death typically within ten years of onset. Mutations in either EPM2A, encoding the glycogen phosphatase laforin, or EPM2B , encoding the E3 ligase malin, cause LD. Whole exome sequencing has revealed many EPM2A variants associated with late-onset or slower disease progression. We established an empirical pipeline for characterizing the functional consequences of laforin missense mutations in vitro using complementary biochemical approaches. Analysis of 26 mutations revealed distinct functional classes associated with different outcomes that were supported by clinical cases. For example, F321C and G279C mutations have attenuated functional defects and are associated with slow progression. This pipeline enabled rapid characterization and classification of newly identified EPM2A mutations, providing clinicians and researchers genetic information to guide treatment of LD patients.

Laforin targets malin to glycogen in Lafora progressive myoclonus epilepsy

“…With the identification of laforin's phosphatase activity and demonstration that it dephosphorylates glycogen, the strong possibility emerged that glycogen over phosphorylation underlies polyglucosan generation ( Ganesh et al, 2000 ; Minassian et al, 1998 ; Tagliabracci et al, 2008 ; Worby et al, 2006 ); however, subsequent work showed that inactivation of laforin's phosphatase, although it leads to glycogen overphosphorylation, is not sufficient to lead to polyglucosan generation or LBs ( Gayarre et al, 2014 ; Nitschke et al, 2017 ). Instead, laforin or malin mutations that disrupt laforin binding to glycogen or to malin, or that inactivate malin's ubiquitin ligase activity, all cause LD ( Brewer et al, 2021 ), indicating that a malin function at glycogen is critical to ensuring glycogen structural integrity. Despite being known to play a crucial role in glycogen metabolism and LD for 20 years, what malin's exact role is has remained unknown in large part because the protein could, until now, not be detected in mouse tissues.…”

“…Finally, laforin appears to bind the E3 ubiquitin ligase malin ( NHLRC1 ) ( Gentry et al, 2005 ; Lohi et al, 2005 ; Sánchez-Martín et al, 2015 ; Solaz-Fuster et al, 2008 ; Vilchez et al, 2007 ; Worby et al, 2008 ), although this has not been confirmed in the native state. Mutations in the laforin or malin genes that disrupt laforin's binding to glycogen, the putative laforin–malin interaction or malin's ubiquitin ligase activity cause LD ( Brewer et al, 2021 ; Chan et al, 2003 ; Fernandez-Sanchez et al, 2003 ; Ganesh et al, 2004 ; Gentry et al, 2005 ; Minassian et al, 1998 ; Wang et al, 2002 ). Introduction of phosphatase-inactive laforin into laforin-knockout LD mice does not correct glycogen overphosphorylation, but does correct glycogen chain lengths and prevents polyglucosan and LB formation ( Gayarre et al, 2014 ).…”

The Toxoplasma glucan phosphatase TgLaforin utilizes a distinct functional mechanism that can be exploited by therapeutic inhibitors

“…3D). To define TgCBM carbohydrate binding, we utilized differential scanning fluorimetry (DSF) (53,54). In the presence of a carbohydrate, an increase in T m is associated with increased protein stability due to protein-ligand interaction.…”

Gene Therapy: Novel Approaches to Targeting Monogenic Epilepsies

“…At presentation, it is challenging to distinguish Lafora disease from idiopathic generalized epilepsies (48). Thus genetic testing is critical, as it reveals pathogenic variants in the EPM2A and EPM2B genes (58). Patients most often receive antiseizure medications, namely valproic acid, which is typically effective at suppressing seizure activity, however the treatment is palliative (59).…”