[Clinical phenotypic and genetic analysis of three children with Paroxysmal kinesigenic dyskinesia and Self-limited familial infantile epilepsy caused by PRRT2 gene mutation].

Objective: To investigate the clinical phenotypic and genetic characteristics of three children with Paroxysmal kinesigenic dyskinesia (PKD) and Self-limited familial infantile epilepsy (SeLIE) caused by PRRT2 gene mutation.

Methods: Three children with PKD and SeLIE caused by PRRT2 gene mutation (children 1-3) who were treated in the First Affiliated Hospital of Zhengzhou University from November 2022 to August 2023 were selected as the research subjects. A retrospective study was conducted to collect the clinical and family history data of the three children. 2 mL of peripheral venous blood from children 1-3 and parents of children 1-2 were collected (parents of children refused to undergo genetic testing and no blood samples were collected), genomic DNA was extracted, whole exome sequencing (WES) was performed, and Sanger sequencing method was used for verification. According to the Classification Standards and Guidelines for Genetic Variants formulated by the American Society of Medical Genetics and Genomics (ACMG) (hereinafter referred to as the "ACMG Guidelines"), the pathogenicity of the variant loci detected in three children was rated, and the detrimental loci of the variant loci were analyzed by multiple bioinformatics software. This study has been approved by the Ethics Committee of the First Affiliated Hospital of Zhengzhou University (Ethics No. 2024-KY-0881-002).

Results: The clinical data and genetic test results of the three children in this study are as follows. Child 1: female, age of onset of 4 months and 10 days, with seizures, manifested as sudden cessation of movements, staring in both eyes, cyanosis of the lips, paleness, and stiffness and shaking of limbs. The results of genetic testing showed that child 1 had maternal PRRT2 gene c.583_584dup (p.P196Afs*34) frameshift variant, which was rated as a pathogenic variant (PVS1 PM2_Supporting PP4) according to ACMG guidelines. According to the clinical manifestations and genetic test results of child 1, he was diagnosed with SeLIE and took oral sodium valproate [0.5 mL/(kg.d)], and was still taking medication at the follow-up of 2 years old, and did not have seizures again after 5 months of age. Child 2: male, age of onset of 10 years old, manifested as dystonia after sudden movement. The results of genetic testing showed that child 2 had PRRT2 gene mutations: paternal c.649dupC (p.R217Pfs*8) frameshift variant and maternal c.445C>A (p.Q149K) mutation. Among them, c.649dupC was a reported pathogenic variant, and according to ACMG guidelines, c.445C>A variant was rated as a variant of unknown clinical significance (PM2_Supporting), with a high probability of benignness. According to the clinical manifestations and genetic test results of the child 2, he was diagnosed with PKD, and was followed up with oral oxcarbazepine 9 mg/(kg.d) until 12 years and 2 months, and was still on the drug, and there was no recurrence of the seizure of the form of dyskinesia after taking the drug. Child 3: male, age of onset of 11 years old, manifested by dystonia after sudden exercise. The results of genetic testing showed that child 3 had a missense variant of PRRT2 gene c.904G>C (p.D302H), and his parents refused genetic testing, and the source of the mutation was unknown, and the variant was rated as a variant of unknown clinical significance (PM2_Supporting+PP3_Moderate+PP4) according to ACMG guidelines. According to the clinical manifestations and genetic test results of child 3, he was diagnosed with PKD, and was treated with oral oxcarbazepine 10 mg/(kg.d) for 1 year and then discontinued on his own, and was followed up at the age of 17, and there was no recurrence of the seizure of the form of movement disorder after taking the drug.

Conclusion: One case of SeLIE and two cases of PKD caused by PRRT2 gene mutations responded well to anti-seizure drugs. In this study, four variant loci of PRRT2 gene were found: c.583_584dup, c.904G>C, c.649dupC, c.445C>A, among which c.583_584dup were new variants, enriching the variant spectrum of PRRT2 gene.