[L-2-hydroxyglutaric aciduria caused by a new mutation in the L2HGDH gene]

In Silico Analysis of the L-2-Hydroxyglutarate Dehydrogenase Gene Mutations and Their Biological Impact on Disease Etiology

The L-2-hydroxyglutarate dehydrogenase (L2HGDH) gene encodes an important mitochondrial enzyme. However, its altered activity results in excessive levels of L-2-hydroxyglutarate, which results in diverse psychiatric features of intellectual disability. In the current study, we executed an in-silico analysis of all reported L2HGDH missense and nonsense variants in order to investigate their biological significance. Among the superimposed 3D models, the highest similarity index for a wild-type structure was shown by the mutant Glu336Lys (87.26%), while the lowest similarity index value was shown by Arg70* (10.00%). Three large active site pockets were determined using protein active site prediction, in which the 2nd largest pocket was shown to encompass the substrate L-2-hydroxyglutarate (L2HG) binding residues, i.e., 89Gln, 195Tyr, 402Ala, 403Gly and 404Val. Moreover, interactions of wild-type and mutant L2HGDH variants with the close functional interactor D2HGDH protein resulted in alterations in the position, number and nature of networking residues. We observed that the binding of L2HG with the L2HGDH enzyme is affected by the nature of the amino acid substitution, as well as the number and nature of bonds between the substrate and protein molecule, which are able to affect its biological activity.

Beyond Isocitrate Dehydrogenase Mutations: Emerging Mechanisms for the Accumulation of the Oncometabolite 2-Hydroxyglutarate

2-Hydroxyglutarate (2-HG) is an unconventional oncometabolite of α-ketoglutarate. Isocitrate dehydrogenase mutation is generally acknowledged to be the main cause of 2-HG accumulation. In isocitrate dehydrogenase mutant tumors, 2-HG accumulation inhibits α-ketoglutarate/Fe(II)-dependent dioxygenases, resulting in epigenetic alterations. Recently, the increase of 2-HG has also been observed in the cases of mitochondrial dysfunction and hypoxia. In these cases, 2-HG not only inhibits α-ketoglutarate/Fe(II)-dependent dioxygenases to regulate epigenetics but also affects other cellular pathways, such as regulating hypoxia-inducible transcription factors and glycolysis. These provide a new perspective for the study of 2-HG.

A novel compound heterozygous mutation of the L2HGDH gene in a Chinese boy with L-2-hydroxyglutaric aciduria: case report and literature review

OBJECTIVE

L-2-hydroxyglutaric aciduria is a genetic metabolic disorder. Its clinical features include elevated levels of hydroxyglutaric acid in body fluids and abnormal magnetic resonance imaging (MRI) in the subcortical white matter, which are affected by the accumulation of L-2-hydroxyglutaric acid.

METHOD

A boy with psychomotor retardation and progressive ataxia accompanied by abnormal brain MRI findings was tested using whole-exome sequencing.

RESULTS

Next-generation sequencing (NGS) revealed two novel compound heterozygous frameshift mutations, c.407 del A (p.K136SfsTer3) and c.699_c700 ins A (p.D234RfsTer42), in the L-2-hydroxyglutarate dehydrogenase (L2HGDH) gene, leading to premature termination codons and truncated FAD/NAD(P)-binding domain of L2HGDH protein. Further laboratory testing revealed an increase in the 2-hydroxyglutaric acid level in the urine.

CONCLUSION

The results suggested that NGS could provide clues for identifying patients with abnormal neuroradiological findings in the subcortical white matter.