Focal seizures and epileptic spasms in a child with Down syndrome from a family with a PRRT2 mutation

Novel and de novo point and large microdeletion mutation in PRRT2-related epilepsy

BACKGROUND

Point and copy number variant mutations in the PRRT2 gene have been identified in a variety of paroxysmal disorders and different types of epilepsy. In this study, we analyzed the phenotypes and PRRT2-related mutations in Chinese epilepsy children.

METHODS

A total of 492 children with epilepsy were analyzed by whole exome sequencing (WES) and low-coverage massively parallel CNV sequencing (CNV-seq) to find the single nucleotide variants and copy number variations (CNVs). And quantitative polymerase chain reaction was utilized to verify the CNVs. Their clinical information was followed up.

RESULTS

We found PRRT2-related mutations in 19 patients (10 males and nine females, six sporadic cases and 13 family cases). Twelve point mutations, four whole gene deletion, and three 16p11.2 deletions were detected. The clinical features of 39 patients in 19 families included one early childhood myoclonic epilepsy (ECME), one febrile seizure (FS), two infantile convulsions with paroxysmal choreoathetosis (ICCA), six paroxysmal kinesigenic dyskinesias (PKD), 12 benign infantile epilepsy (BIE), and 17 benign familial infantile epilepsy (BFIE). All patients had normal brain MRI. Interictal EEG showed only one patient had generalized polyspike wave and five patients had focal transient discharges. Focal seizures originating in the frontal region were recorded in one patient, two from the temporal region, and two from the occipital region. Most patients were treated effectively with VPA or OXC, and the child with myoclonic seizures was not sensitive to antiepileptic drugs.

CONCLUSION

PRRT2 mutations can be inherited or de novo, mainly inherited. The clinical spectrum of PRRT2 mutation includes BIE, BFIE, ICCA, PKD, FS, and ECME. The PRRT2-related mutations contained point mutation, whole gene deletion and 16p11.2 deletions, and large microdeletion mutations mostly de novo. It is the first report of PRRT2 mutation found in ECME. Our report expands the mutation and clinical spectrum of PRRT2-related epilepsy.

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.

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

PURPOSE OF THE STUDY

Though rare, children are susceptible to paroxysmal dyskinesias such as paroxysmal kinesigenic dyskinesia, and infantile convulsions and choreoathetosis. Recent studies showed that the cause of paroxysmal kinesigenic dyskinesia or infantile convulsions and choreoathetosis could be proline-rich transmembrane protein 2 (PRRT2) gene mutations.

MATERIAL AND METHODS

This study analysed PRRT2 gene mutations in 51 families with paroxysmal kinesigenic dyskinesia or infantile convulsions and choreoathetosis by direct sequencing. In particular, we characterize the genotype-phenotype correlation between age at onset and the types of PRRT2 mutations in all published cases.

RESULTS

Direct sequencing showed that 12 out of the 51 families had three different pathogenic mutations (c.649dupC, c.776dupG, c.649C>T) in the PRRT2 gene. No significant difference of age at onset between the patients with and without PRRT2 mutations was found in this cohort of patients. A total of 97 different PRRT2 mutations have been reported in 87 studies till now. The PRRT2 mutation classes are wide, and most mutations are frameshift mutations but the most common mutation remains c.649dupC. Comparisons of the age at onset in paroxysmal kinesigenic dyskinesia or infantile convulsions patients with different types of mutations showed no significant difference.

CONCLUSIONS

This study expands the clinical and genetic spectrums of Chinese patients with paroxysmal kinesigenic dyskinesia and infantile convulsions and choreoathetosis. No clear genotype-phenotype correlation between the age at onset and the types of mutations has been determined.

The Clinical Spectrum of Benign Epilepsy with Centro-Temporal Spikes: a Challenge in Categorization and Predictability

Benign epilepsy with centro-temporal spikes (BECTS) is the most common type of focal epilepsy in children; it is age-dependent and presumably genetic. Traditionally, children with BECTS have a very good prognosis, even without medical treatment, and are thought to show no neurological symptoms or cognitive deficits. However, many previous studies have shown that BECTS can present with various clinical and electroencephalographic characteristics that are commonly associated with neuropsychological deficits, including linguistic, cognitive, and behavioral impairment. The degree of the neuropsychological deficits appears to depend on the sleep cycle and the localization of epileptiform discharges. Furthermore, based on neurobiological studies, a complex interplay between the processes of brain maturation and the involvement of genes that confer susceptibility may contribute to a variety of different childhood epileptic syndromes with various neuropsychological deficits. Thus, BECTS, atypical benign focal epilepsy during childhood, status epilepticus of BECTS, Landau-Kleffner syndrome, and epileptic encephalopathy with continuous spike-and-wave during sleep are all considered different entities, but are part of a single spectrum of disorders. In clinical practice, we have to consider BECTS as benign only when there are no or only mild neuropsychological deficits before medical treatment.