PRRT2 mutations in a cohort of Chinese families with paroxysmal kinesigenic dyskinesia and genotype-phenotype correlation reanalysis in literatures

Long-term low-dose lamotrigine for paroxysmal kinesigenic dyskinesia: a two-year investigation of cognitive function in children

Objective

While low-dose lamotrigine has shown effectiveness in managing paroxysmal kinesigenic dyskinesia (PKD) in pediatric populations, the cognitive consequences of extended use are yet to be fully elucidated. This study seeks to assess the evolution of cognitive functions and the amelioration of attention deficit and hyperactivity disorder (ADHD) symptoms following a two-year lamotrigine treatment in children.

Methods

This investigation employed an open-label, uncontrolled trial design. Between January 2008 and December 2021, thirty-one participants, ranging in age from 6.5 to 14.1 years, were enrolled upon receiving a new diagnosis of PKD, as defined by the clinical diagnostic criteria set by Bruno in 2004. Comprehensive evaluation of PRRT2 variants and 16p11.2 microdeletion was achieved using whole-exome sequencing (WES) and bioinformatics analysis of copy number variant (CNV) for all subjects. Immediately after diagnosis, participants commenced treatment with low-dose lamotrigine. Cognitive function was assessed using the Wechsler Intelligence Scale for Children-Chinese Revised (WISC-CR) at baseline and after 2 years, with ADHD diagnoses and symptom severity simultaneously assessed by experts in accordance with the DSM-IV diagnostic criteria for ADHD and the ADHD Rating Scale-IV (ADHD-RS-IV).

Results

Initially, twelve out of 31 patients (38.7%) presented with comorbid ADHD. The latency to treatment initiation was notably longer in PKD patients with ADHD (30.75 ± 12.88 months) than in those without ADHD (11.66 ± 9.08 months), t = 4.856, p<0.001. Notably, patients with a latency exceeding 2 years exhibited a heightened risk for comorbid ADHD (OR = 4.671, P=0.015) in comparison to those with shorter latency. Out of the cohort, twenty-five patients saw the clinical trial to its completion. These individuals demonstrated a marked elevation in WISC-CR scores at the 2-year mark relative to the outset across FSIQ (baseline mean: 108.72 ± 10.45 vs 24 months: 110.56 ± 10.03, p=0.001), VIQ (baseline mean: 109.44 ± 11.15 vs 24 months: 110.80 ± 10.44, p=0.028), and PIQ domains (baseline mean: 106.52 ± 9.74 vs 24 months: 108.24 ± 9.38, p=0.012). Concurrently, a substantial mitigation was observed in ADHD inattention at 2 years compared to baseline (p<0.001), with an average total subscale scores decrement from 9.04 ± 4.99 to 6.24 ± 4.05.

Conclusion

Prolonged duration of untreated PKD in children may elevate the risk of ADHD comorbidity. Notably, following a 2-year lamotrigine regimen, enhancements were observed in both cognitive test outcomes and ADHD symptomatology.

PRRT2 Mutation and Serum Cytokines in Paroxysmal Kinesigenic Dyskinesia

OBJECTIVE

Paroxysmal kinesigenic dyskinesia (PKD) is a rare movement disorder PRRT2 gene mutations have been reported to cause PKD. However, the pathophysiological mechanism of PKD remains unclear, and it is unknown whether an inflammatory response is involved in the occurrence of this disease. We aimed to investigate the symptomatology, genotype, and serum cytokines of patients with PKD.

METHODS

We recruited 21 patients with PKD, including 7 with familial PKD and 14 with sporadic PKD. Their clinical features were investigated, and blood samples were collected, and PRRT2 mutations and cytokine levels were detected.

RESULTS

The mean age at PKD onset was 12.3±2.2 years old. Dystonia was the most common manifestation of dyskinesia, and the limbs were the most commonly affected parts. All attacks were induced by identifiable kinesigenic triggers, and the attack durations were brief (<1 min). Four different mutations from 9 probands were identified in 7 familial cases (71.4%) and 14 sporadic cases (28.6%). Two of these mutations (c.649dupC, c.620_621delAA) had already been reported, while other 2 (c.1018_1019delAA, c.1012+1G>A) were previously undocumented. The tumor necrosis factor (TNF)-α level in the PKD group was significantly higher than that in the age- and sex-matched control group (P=0.025). There were no significant differences in the interleukin (IL)-1β, IL-2R, IL-6, IL-8, or IL-10 levels between the two groups.

CONCLUSION

In this study, we summarized the clinical and genetic characteristics of PKD. We found that the serum TNF-α levels were elevated in patients clinically diagnosed with PKD, suggesting that an inflammatory response is involved in the pathogenesis of PKD.

A Clinical and Integrated Genetic Study of Isolated and Combined Dystonia in Taiwan

Dystonia is a clinically and genetically heterogeneous movement disorder. However, genetic causes of dystonia remain largely unknown in Asian subjects. To address this, we applied an integrated two-step approach that included gene dosage analysis and a next-generation sequencing panel containing 72 known genes causative for dystonia and related movement disorders to 318 Taiwanese patients with isolated or combined dystonia. Whole-genome sequencing was performed for one multiplex family with no known causative variant. The panel confirmed the genetic diagnosis in 40 probands (12.6%). A genetic diagnosis was more likely with juvenile onset compared with adult onset (24.2% vs 10.8%; P = 0.03) and those with combined features, especially with myoclonus, compared with isolated dystonia (35.3% vs 10.5%; P = 0.004). The most common causative genes were SGCE followed by GCH1, TH, CACNA1B, PRRT2, MR1, CIZ1, PLA2G6, and PRKN. Genetic causes were identified from single cases in TOR1A, TUBB4A, THAP1, ATP1A3, ANO3, GNAL, KMT2B, SLC6A3, ADCY5, CYP27A1, PANK2, C19orf12, and SPG11. The whole-genome sequencing analysis identified a novel intragenic deletion in OPHN1 in a multiplex family with X-linked dystonia and intellectual delay. Our findings delineate the genetic architecture and clinical spectrum of dystonia-causing pathogenic variants in an Asian population.

Characteristics of infantile convulsions and choreoathetosis syndrome caused by PRRT2 mutation

Importance

Infantile convulsions and choreoathetosis (ICCA) is a rare neurological disorder. Many affected patients are either misdiagnosed or prescribed multiple antiepileptic drugs.

Objective

To explore therapeutic drug treatments and dosages for ICCA in children.

Methods

Detailed clinical features (e.g., past medical history and family history), genetic features, and treatment outcomes were collected from the records of six patients with ICCA.

Results

Mean age at paroxysmal kinesigenic dyskinesia (PKD) onset was 8 years 8 months (range, 3–12 years); the clinical presentation was characterized by daily short paroxysmal episodes of dystonia/dyskinesia. All patients had infantile convulsions at less than 1 year of age, and the mean onset age was 5.5 months (range, 4–7 months). Two patients had a family history of ICCA, PKD, or benign familial infantile epilepsy. Whole exome sequencing identified the c.649–650insC mutation in PRRT2 in six patients; three mutations were inherited and three were de novo. All patients were prescribed low‐dose carbamazepine and showed dramatic improvement with the complete disappearance of dyskinetic episodes after 3 days. They attended follow‐up for 5–17 months and were attack‐free until the final follow‐up.

Interpretation

PRRT2 mutations are the primary cause of ICCA. Low‐dose carbamazepine monotherapy is effective and well‐tolerated in children.

PRRT2 variants and effectiveness of various antiepileptic drugs in self-limited familial infantile epilepsy

PURPOSE

Self-limited familial infantile epilepsy (SFIE) is largely associated with variants in proline-rich transmembrane protein 2 (PRRT2). However, the detailed phenotype-genotype correlations are unclear, along with the efficacy of various antiepileptic drugs in the treatment of this epilepsy syndrome. In this study, we analysed the PRRT2 variants associated with SFIE in Chinese patients, and the efficacy of different antiepileptic drugs prescribed during follow-up.

METHODS

We retrospectively included 20 patients diagnosed with SFIE and reviewed their clinical characteristics, genetic variants, and treatment responses.

RESULTS

Eighteen of the 20 (90%) patients harboured the common heterozygous variant of PRRT2 c.649dupC p.(Arg217fs). One patient had two heterozygous variants of PRRT2, c.640G>C p.(Ala214Pro) and c.955G>T p.(Val319Leu), and the other patient harboured a novel c.606delA (p.Pro203Hisfs) variant. Nine patients who had first-line treatment of oxcarbazepine (OXC) became seizure-free. However, initial treatment with levetiracetam (LEV) or sodium valproate (VPA) in eight and three patients, respectively, was not effective even after increasing the dosage, and seizure-free status was only achieved after changing the treatment to OXC. The treatment responses suggested a significant difference (P < 0.001) between OXC and other anti-epileptic drugs.

CONCLUSION

OXC as a sodium channel blocker may have a better effect than LEV and VPA in the treatment of PRRT2-associated SFIE. PRRT2 variants may be used as a biomarker to help select antiepileptic drugs for SFIE.

PRRT2 Related Epilepsies: A Gene Review

PRRT2 encodes for proline-rich transmembrane protein 2 involved in synaptic vesicle fusion and presynaptic neurotransmitter release. Mutations in human PRRT2 have been related to paroxysmal kinesigenic dyskinesia (PKD), infantile convulsions with choreoathetosis, benign familial infantile epilepsies, and hemiplegic migraine. PRRT2 mutations cause neuronal hyperexcitability, which could be related to basal ganglia or cortical circuits dysfunction, leading to paroxysmal disorders. PRRT2 is expressed in the cerebral cortex, basal ganglia, and cerebellum. Approximately, 90% of pathogenic variants are inherited and 10% are de novo. Paroxysmal attacks in PKD are characterized by dystonia, choreoathetosis, and ballismus. In the benign familial infantile epilepsy (BFIE), seizures are usually focal with or without generalization, usually begin between 3 and 12 months of age and remit by 2 years of age. In 30% of cases of PRRT2-associated PKD, there is an association with BFIE, and this entity is referred to as PKD with infantile convulsions (PKD/IC). PRRT2 mutations are the cause of benign family childhood epilepsy and PKD/IC. On the other hand, PRRT2 mutations do not seem to correlate with other types of epilepsy. The increasing incidence of hemiplegic migraine in families with PRRT2-associated PKD or PKD/IC suggests a common disease pathway, and it is possible to assert that BFIE, paroxysmal kinesigenic dyskinesia, and PKD with IC belong to a continuous disease spectrum of PRRT2-associated diseases.

Novel PRRT2 gene variants identified in paroxysmal kinesigenic dyskinesia and benign familial infantile epilepsy in Chinese families

The present study was performed to investigate the clinical manifestations and pathogenic variants in three large families with autosomal dominant paroxysmal kinesigenic dyskinesia (PKD) and/or benign familial infantile epilepsy (BFIE) in China. Detailed clinical data and family history were collected. Genomic DNA was isolated from the peripheral blood samples of all available members. The genetic diagnosis was made by whole-exome sequencing on the three probands and the candidate variants were verified by PCR-Sanger sequencing. The pathogenicity of variants was predicted by bioinformatics analyses and classified according to the American College of Medical Genetics criteria. A total of three causative heterozygous variants were identified in the proline-rich transmembrane protein 2 (PRRT2) gene by DNA sequencing: A novel c.324_334del(p.Val109Argfs*21) deletion variant in Family A, as well as the previously known c.510_513del(p.Ser172Argfs*3) deletion variant in Family B and c.649dupC(p.Arg217Profs*8) duplication variant in Family C. The three variants of PRRT2 co-segregated with the phenotype and genotype in the family members. The present results deepen the current understanding of PKD/BFIE and extend the genotypic-phenotypic spectrum of PKD/BFIE.

Neural Mechanisms of Paroxysmal Kinesigenic Dyskinesia: Insights from Neuroimaging

Paroxysmal kinesigenic dyskinesia (PKD) is a rare movement disorder of the nervous system, and little is known about its pathogenesis. Currently, the diagnosis of PKD is primarily based on clinical manifestations, with little objective evidence. Neuroimaging has been used to explore the pathological changes in cerebral structure and function associated with PKD. The current review highlights recent advances in neuroimaging to provide a better understanding of the neural mechanisms and early diagnosis of this disorder. Several studies utilizing single-photon emission computed tomography (CT), positron emission tomography, and structural and functional magnetic resonance imaging have found significant localized abnormalities in the caudate nucleus, putamen, pallidum, thalamus, and frontoparietal cortex in PKD patients. These studies have also revealed alterations in interhemispheric functional connectivity between the brain regions of bilateral cerebral hemispheres such as the putamen, primary motor cortex, supplementary motor area, dorsal lateral prefrontal cortex, and primary somatosensory cortex in these patients. In addition, proline-rich transmembrane protein 2 gene mutations can affect the functional organization of the brain in PKD. These results suggest that the neural mechanisms of PKD are associated with the disruption of both structural and/or functional properties in basal ganglia-thalamo-cortical circuitry and interhemispheric functional connectivity. PKD can be considered a circuitry/network disorder and is not restricted to localized structural and/or functional abnormalities. Multimodal neuroimaging combined with gene analysis can provide additional valuable information for a better understanding of the pathogenesis and early diagnosis of this disorder.

Neurodevelopmental trajectory and modifiers of 16p11.2 microdeletion: A follow-up study of four Chinese children carriers

Background

Neurodevelopmental disorders (NDDs) are a group of disorders with high genetic and phenotypic heterogeneities. The 16p11.2 microdeletion has been implicated as an important genetic risk factor for NDDs.

Methods

Multiple genetic tests were used to detect the 16p11.2 microdeletion from 918 Chinese children with NDDs. Targeted sequencing of genes in the 16p11.2 interval was performed in all carriers of the 16p11.2 microdeletion, and whole‐genome expression profiling analysis was performed for the patient carriers and normal carriers in their intra‐family.

Results

Three patients carrying the 16p11.2 microdeletion were screened out, indicating a frequency of 0.33% for the 16p11.2 microdeletion in this cohort. We reviewed the neurodevelopmental trajectories of the 16p11.2 microdeletion carriers from childhood to puberty and confirmed that this microdeletion was associated with abnormal neurodevelopment, with varied neurodevelopmental phenotypes. A differential PRRT2 genotype (rs10204, T>C) was identified between patients and normal carriers of the 16p11.2 microdeletion. Moreover, the determination of differential whole‐genome expression profiling demonstrated the destruction of the top‐ranked network in neurogenesis and accounted for observation of abnormal neurodevelopmental phenotypes in the 16p11.2 microdeletion carriers.

Conclusions

We have provided the frequency of the 16p11.2 microdeletion in a Chinese pediatric NDD cohort with a variable NDD phenotype from childhood to puberty, which is useful for Chinese geneticists/pediatricians to conduct the 16p11.2 microdeletion testing in children with NDDs.

Novel mutation of the PRRT2 gene in two cases of paroxysmal kinesigenic dyskinesia: Two case reports

Paroxysmal kinesigenic dyskinesia (PKD) is a rare condition characterized by recurrent brief episodes of dystonia, chorea, athetosis or any combination of these, without alterations of consciousness. The proline-rich transmembrane protein 2 (PRRT2) gene has been widely investigated as a causative gene of PKD. To date, a cluster of pathogenic variants associated with PKD have been identified in the PRRT2 gene. In the present case report, two Chinese patients with sporadic PKD are discussed. Genetic analysis revealed a de novo heterozygous missense mutation, c.955G>T (p.Val319Leu) in exon 3 of the PRRT2 gene. Compared with the commonly reported clinical manifestation of PRRT2-associated PKD, the patients in this report showed several primary distinctive features. The mutations identified in the present analysis expand upon the mutation spectrum of the PRRT2 gene, and this newly found variant further reinforces the importance of the PRR2 gene in PKD.

PRRT2 gene variant in a child with dysmorphic features, congenital microcephaly, and severe epileptic seizures: genotype-phenotype correlation?

Background

Mutations in Proline-rich Transmembrane Protein 2 (PRRT2) have been primarily associated with individuals presenting with infantile epilepsy, including benign familial infantile epilepsy, benign infantile epilepsy, and benign myoclonus of early infancy, and/or with dyskinetic paroxysms such as paroxysmal kinesigenic dyskinesia, paroxysmal non-kinesigenic dyskinesia, and exercise-induced dyskinesia. However, the clinical manifestations of this disorder vary widely. PRRT2 encodes a protein expressed in the central nervous system that is mainly localized in the pre-synaptic neurons and is involved in the modulation of synaptic neurotransmitter release. The anomalous function of this gene has been proposed to cause dysregulation of neuronal excitability and cerebral disorders.

Case presentation

We hereby report on a young child followed-up for three years who presents with a spectrum of clinical manifestations such as congenital microcephaly, dysmorphic features, severe intellectual disability, and drug-resistant epileptic encephalopathy in association with a synonymous variant in PRRT2 gene (c.501C > T; p.Thr167Ile) of unknown clinical significance variant (VUS) revealed by diagnostic exome sequencing.

Conclusion

Several hypotheses have been advanced on the specific role that PRRT2 gene mutations play to cause the clinical features of affected patients. To our knowledge, the severe phenotype seen in this case has never been reported in association with any clinically actionable variant, as the missense substitution detected in PRRT2 gene. Intriguingly, the same mutation was reported in the healthy father: the action of modifying factors in the affected child may be hypothesized. The report of similar observations could extend the spectrum of clinical manifestations linked to this mutation.