Atypical juvenile presentation of GM2 gangliosidosis AB in a patient compound-heterozygote for c.259G & gt;T and c.164C & gt;T mutations in the GM2A gene

We describe a 9-year-old child with an unusual juvenile clinical onset of GM2-gangliosidosis AB. At the age of 3years he presented with global developmental delay, progressive epilepsy, intellectual disability, axial hypertonia, spasticity, seizures and ataxia, but without the macular cherry-red spots typical for GM2 gangliosidosis. Brain MRI detected a rapid onset of diffuse atrophy, whereas whole exome sequencing showed that the patient is a compound heterozygote for two mutations in GM2A: a novel nonsense mutation, c.259G>T (p.E87X) and a missense mutation c.164C>T (p.P55L) that was recently identified in homozygosity in patients of a Saudi family with a progressive chorea-dementia syndrome. Western blot analysis showed an absence of GM2AP in cultured fibroblasts from the patient, suggesting that both mutations interfere with the synthesis and/or folding of the protein. Finally, impaired catabolism of GM2 ganglioside in the patient's fibroblasts was demonstrated by metabolic labeling with fluorescently labeled GM1 ganglioside and by immunohistochemistry with anti-GM2 and anti-GM3 antibodies. Our observation expands the molecular and clinical spectrum of molecular defects linked to GM2-gangliosidosis and suggests novel diagnostic approach by whole exome sequencing and perhaps ganglioside analysis in cultured patient's cells.
Source: Molecular Genetics and Metabolism Reports - Category: Genetics & Stem Cells Source Type: research