Paroxysmal Dyskinesia in Children: from Genes to the Clinic

BACKGROUND AND PURPOSE: Paroxysmal dyskinesia is a genetically and clinically heterogeneous movement disorder. Recent studies have shown that it exhibits both phenotype and genotype overlap with other paroxysmal disorders as well as clinical heterogeneity. We investigated the clinical and genetic characteristics of paroxysmal dyskinesia in children. METHODS: Fifty-five patients (16 from 14 families and 39 sporadic cases) were enrolled. We classified them into three phenotypes: paroxysmal kinesigenic dyskinesia (PKD), paroxysmal nonkinesigenic dyskinesia (PNKD), and paroxysmal exercise-induced dyskinesia (PED). We sequenced PRRT2, SLC2A1, and MR-1 in these patients and reviewed their medical records. RESULTS: Forty patients were categorized as PKD, 14 as PNKD, and 1 as PED. Thirty-eight (69.1%) patients were male, and their age at onset was 8.80±4.53 years (mean±SD). Dystonia was the most common symptom (38 patients, 69.1%). Pathogenic variants were identified in 20 patients (36.4%): 18 with PRRT2 and 2 with SLC2A1. All of the patients with PRRT2 mutations presented with PKD alone. The 2 patients carrying SLC2A1 mutations presented as PNKD and PED, and one of them was treated effectively with a ketogenic diet. Six mutations in PRRT2 (including 2 novel variants) were identified in 9 of the 13 tested families (69.2%) and in 8 patients of the 25 tested sporadic cases (32.0%). There were no significant differences in clinical features or drug response between the PRRT2-positive and PRRT2-negative PKD groups. CONCLUSIONS: This study has summarized the clinical and genetic heterogeneity of paroxysmal dyskinesia in children. We suggest that pediatric paroxysmal dyskinesia should not be diagnosed using clinical features alone, but by combining them with broader genetic testing.

De novo KCNMA1 mutations in 3 children with paroxysmal nonkinesigenic dyskinesia and developmental delay / 中华实用儿科临床杂志

Objective To analyze the clinical characteristics of 3 unrelated boys with paroxysmal nonkinesigenic dyskinesia and developmental delay caused by de novo mutation in KCNMA1,and to expand the knowledge of clinical phenotype of KCNMA1 mutation.Methods Clinical data of patients were collected,including gender,age,condition of the perinatal period,personal history,and family history.And the features of genotype data were collected including features of attack,developmental milestones,physical examinations,treatments,and responses to treatment.The data including blood biochemical results,results of metabolic screening and genetic testing and the pedigree validation were collected,while the relationship between phenotype and genotype was analyzed.Results (1)Phenotypic features:3 unrelated boys were diagnosed.The ages of disease onset were 20 days,7 months and 13 months,respectively.All the patients manifested paroxysmal nonkinesigenic dyskinesia and were characterized by the episodes that occurred during wakefulness,presented with sudden onset of asymmetric limb dystonic posture,sometimes with nystagmus and strabismus,or sudden decrease of voluntary movement of limbs with hypotonia and occasional esotropia and yawning.There was no loss of awareness during attack.No precipitating factors were observed before attacks.The developmental milestones were delayed.Three children had no response to anti-epilepsy drug before diagnosis.After diagnosis,2 cases used Clonazepam and 1 case showed less attack.There was not any epileptic seizure until the last follow-up at the ages of 3 years and 6 months old,7 years old,and 5 years and 8 months old,respectively.The frequency of attacks was decreased.The episodes were recorded during video-electroencephalogram(EEG) monitoring,which showed normal ictal and interictal EEG.(2)Genotypic features:all 3 children were detected to have KCNMA1 genetic heterozygous missense mutation,while c.2650G>A (p.Glu884Lys) mutation was identified in 1 patient,and c.3158A>G(p.Asn1053Ser)mutation in the other 2 patients,but no such mutation was found in their parents.Conclusion This finding expands the phenotype of KCNMA1mutation.KCNMA1 should be considered as one of the candidate genes for screening in patients with early onset of paroxysmal nonkinesigenic dyskinesia without triggers,or early-onset of developmental delay,with or without epilepsy.