Clinical and Genetic Analysis of L-2-Hydroxyglutaric Aciduria Caused by a Novel L2HGDH Mutation with a Concurrent RYR1 Variant

Background/Objectives: L-2-hydroxyglutaric aciduria (L2HGA) is a rare autosomal recessive neurometabolic disorder marked by developmental delay, intellectual disability, and progressive movement abnormalities. Variants in RYR1 can cause congenital myopathies, but data on the co-occurrence of variants in populations are limited. The aim of this study was to characterize the clinical and genetic basis of the neurometabolic and neuromuscular abnormalities and to investigate the potential interaction between the identified variants. Methods: Patients with complex, previously undiagnosed clinical presentations underwent neurological evaluation, including brain magnetic resonance imaging, electromyography, biochemical testing, and whole-exome sequencing (WES). Identified variants were analyzed in silico and confirmed by Sanger sequencing in the patient and her parents. Three cases were reviewed, and one of these patients exhibited developmental delay, hypotonia, intellectual disability, and progressive motor dysfunction. Biochemical tests revealed markedly elevated urinary 2-hydroxyglutaric acid levels, consistent with L2HGA. Results: WES identified a homozygous likely pathogenic variant in L2HGDH (c.589_590insGGC, p.Q197insG), confirming the molecular diagnosis of L2HGA. In addition, a heterozygous missense variant in RYR1 (c.7268T>A, p.M2423K), classified as a variant of uncertain significance, was detected and was inherited from her mildly affected father. The L2HGDH variant explains the neurometabolic phenotype of the patient, whereas the RYR1 variant remains of uncertain significance, and its clinical contribution cannot be clearly established. Conclusions: To our knowledge, this case illustrates the co-occurrence of a likely pathogenic L2HGDH variant and a heterozygous RYR1 variant of uncertain significance. The findings expand the mutational spectrum of L2HGA and underscore the value of comprehensive genomic testing in complex neurometabolic and neuromuscular disorders.