Congenital myasthenic syndrome with mild intellectual disability caused by a recurrent SLC25A1 variant.

European journal of human genetics : EJHG 2020 Mar

filter terms:

Congenital myasthenic syndromes (CMS) are a clinically and genetically heterogeneous group of disorders caused by mutations which lead to impaired neuromuscular transmission. SLC25A1 encodes a mitochondrial citrate carrier, associated mainly with the severe neurometabolic disease combined D-2- and L-2-hydroxyglutaric aciduria (D/L-2-HGA). We previously reported a single family with a homozygous missense variant in SLC25A1 with a phenotype restricted to relatively mild CMS with intellectual disability, but to date no additional cases of this CMS subtype had been reported. Here, we performed whole exome sequencing (WES) in three additional and unrelated families presenting with CMS and mild intellectual disability to identify the underlying causative gene. The WES analysis revealed the presence of a homozygous c.740G>A; p.(Arg247Gln) missense SLC25A1 variant, the same SLC25A1 variant as identified in the original family with this phenotype. Electron microscopy of muscle from two cases revealed enlarged and accumulated mitochondria. Haplotype analysis performed in two unrelated families suggested that this variant is a result of recurrent mutation and not a founder effect. This suggests that p.(Arg247Gln) is associated with a relatively mild CMS phenotype with subtle mitochondrial abnormalities, while other variants in this gene cause more severe neurometabolic disease. In conclusion, the p.(Arg247Gln) SLC25A1 variant should be considered in patients presenting with a presynaptic CMS phenotype, particularly with accompanying intellectual disability.

Citation

Sunitha Balaraju, Ana Töpf, Grace McMacken, Veeramani Preethish Kumar, Astrid Pechmann, Helen Roper, Seena Vengalil, Kiran Polavarapu, Saraswati Nashi, Niranjan Prakash Mahajan, Ines A Barbosa, Charu Deshpande, Robert W Taylor, Judith Cossins, David Beeson, Steven Laurie, Janbernd Kirschner, Rita Horvath, Robert McFarland, Atchayaram Nalini, Hanns Lochmüller. Congenital myasthenic syndrome with mild intellectual disability caused by a recurrent SLC25A1 variant. European journal of human genetics : EJHG. 2020 Mar;28(3):373-377