Pediatric, Paroxysmal, and Rare Neurometabolic Diseases

Objective: To develop a targeted gene panel for Paroxysmal Movement Disorders using Whole Exome Sequencing.Background: Paroxysmal movement disorders (PMDs) are a neurological disorder, characterized by occurrence of episodic involuntary attacks of abnormal movements.PMDs are broadly classified into Paroxysmal dyskinesia and episodic ataxia.Genetics has played a significant part in understanding the mechanism involved in disease development, but so far had relatively less impact on the treatment of PMDs (1).The clinical symptoms of many paroxysmal disorders are overlapping in nature, which results in inappropriate classification of PMDs.Hence, to overcome this non-specificity, we have selected 30 genes linked to various PMDs and developed a gene panel for better classification.Methods: In this study, a total of 165 samples (93 PMD patients and 72 family members) were recruited from different hospitals across India.DNA was extracted from all these samples using Spin-Column method (Qiagen Kit, Germany).Sanger sequencing was performed on 127 samples (93 PMD patients and 34 family members) for PRRT2 gene, as described by Prabhakara et al., 2021(2).Whole Exome Sequencing (WES) was performed for PMD samples that were negative for PRRT2 mutation to identify other candidate genes and mutations.The newly identified genes and their variants were analyzed with phenotype-genotype correlation, pathogenicity, and associated clinical factors as per ACMG guidelines (3).Results: Upon Sanger sequencing of 93 PMD patients, 19 turned PRRT2 positive with various mutations [c.649dupC (p.Arg217Profs*8), c.649C>T (p.Arg217*), c.696G>C (p.His232Glu), c.649delC (p.-Arg217fs)].The WES data showed genes such as PRRT2, TMEM151A, ANO3, SCN1A, SCN8A, DLAT, CACNA1A, ATP1A3, ATP1A2, KMT2B, Y1F1B and IREB2 played significant role in the PMD phenotypes.Based on our WES results and through a literature survey, we have designed a gene panel for PMDs consisting of 30 genes, and the list of candidate genes is shown in table 1.Conclusions: The selected 30 genes will be helpful to interpret and classify the PMD subtype from other overlapping neurological disorders with improved specificity and accuracy by identifying specific gene mutations.The designed gene panel will provide further evidence for the precise diagnosis of the disease and will help in treating patients through appropriate drugs with targeted therapy.