Case analysis of epilepsy, neurodevelopmental disorder, and motor disorders associated with mutations in the dehydrodolichyl diphosphate synthase gene

Abstract

The objective of this study is to analyze the role of dehydrodolichyl diphosphate synthase (DHDDS), a crucial enzyme in the mevalonate pathway, and its encoded mutations in the onset of developmental delay and seizures, with or without movement abnormalities. Its genotype-phenotype characteristics are still inconclusive. We analyzed the clinical characteristics of epilepsy, and neurodevelopmental and motor disorders related to DHDDS gene mutations and report the genotype-phenotype characteristics of a child with epilepsy caused by DHDDS gene mutation, providing a summary and a statistical analysis of epilepsy cases associated with DHDDS gene mutation up until February 2022.

Methods: Using "DHDDS; epilepsy; neurodevelopmental disorder" as the keywords, the literature relevant to DHDDS gene mutations up until February 2022 was reviewed. A total of 25 cases were retrieved, among which 21 cases with complete data were included in the chi-squared test. The clinical characteristics of DHDDS gene-related cases were summarized and analyzed.

Results: The onset of epilepsy caused by mutations of the DHDDS gene typically occurs during infancy. Predominantly, the mutation occurs in the locus of c.632G>A p.R211Q. Myoclonus is frequently the initial manifestation of epilepsy; it frequently coexists with neurodevelopmental disorder and intellectual disability, and patients have no specific type of motor disorder. Cranial magnetic resonance imaging (MRI) reveals no abnormalities, whereas electroencephalogram (EEG) frequently exhibits abnormalities. Valproic acid (VPA) yields good curative effects.

Conclusion: Mutations in the DHDDS gene are associated with congenital glycosylation disorder, autosomal recessive retinitis pigmentosa, and epilepsy. According to statistical analysis using the chi-squared test, for pediatric patients with mutations in this gene locus, most of the epilepsy types are myoclonic epilepsies with intellectual disability and neurodevelopmental disorders. They have normal brain MRIs and abnormal EEGs. VPA produces beneficial therapeutic results and the differences are all statistically significant. The current diagnosis still relies on next-generation sequencing or whole-exome sequencing.

Keywords: DHDDS; Epilepsy; Intellectual disability; Neurodevelopmental disorder; VPA.