Evaluation of iron deposition in the motor CSTC loop of a Chinese family with paroxysmal kinesigenic dyskinesia using quantitative susceptibility mapping

Introduction

Previous studies have revealed structural, functional, and metabolic changes in brain regions inside the cortico-striatal-thalamo-cortical (CSTC) loop in patients with paroxysmal kinesigenic dyskinesia (PKD), whereas no quantitative susceptibility mapping (QSM)-related studies have explored brain iron deposition in these areas.

Methods

A total of eight familial PKD patients and 10 of their healthy family members (normal controls) were recruited and underwent QSM on a 3T magnetic resonance imaging system. Magnetic susceptibility maps were reconstructed using a multi-scale dipole inversion algorithm. Thereafter, we specifically analyzed changes in local mean susceptibility values in cortical regions and subcortical nuclei inside the motor CSTC loop.

Results

Compared with normal controls, PKD patients had altered brain iron levels. In the cortical gray matter area involved with the motor CSTC loop, susceptibility values were generally elevated, especially in the bilateral M1 and PMv regions. In the subcortical nuclei regions involved with the motor CSTC loop, susceptibility values were generally lower, especially in the bilateral substantia nigra regions.

Conclusion

Our results provide new evidence for the neuropathogenesis of PKD and suggest that an imbalance in brain iron levels may play a role in PKD.

Complicated paroxysmal kinesigenic dyskinesia associated with SACS mutations

Background

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is caused by pathogenic variants in the SACS gene and is characterized by ataxia, peripheral neuropathy, pyramidal impairment and episodic conditions such as epilepsy. Paroxysmal kinesigenic dyskinesia (PKD) had not been previously described in ARSACS.

Methods

We analyzed clinical manifestations and performed whole-exome sequencing (WES) in two independent patients with ARSACS and PKD. Both patients' parents were unaffected. Genetic data were filtered for potential pathogenic variants, searching for de novo mutations suggestive of a dominant disease model or homozygous and compound heterozygous variants of a recessive model. Potential mutations that existed in both patients were generated and subjected to Sanger sequencing. The WES results of 163 PKD patients without additional symptoms from previous experiments were also reviewed.

Results

Novel compound heterozygous mutations in the SACS gene were identified in Patient 1 (p.P3007S and p.H3392fs), and a novel homozygous truncating mutation (p.W1376X) was identified in Patient 2. In both patients, each mutant allele was inherited from one of his or her unaffected parents. All 3 mutations were absent in 196 ethnic-matched control chromosomes or in data from the 1000 Genomes Project. No pathogenic variants associated with paroxysmal diseases, especially PKD and episodic ataxia, were identified. In PKD patients without additional symptoms, no homozygous or compound heterozygous variants in the SACS gene were detected.

Conclusions

This study expands the clinical phenotype of ARSACS and suggests the inclusion of SACS screening in patients with PKD plus ARSACS.

Quick Flicks: Association of Paroxysmal Kinesigenic Dyskinesia and Tics

Background

Paroxysmal kinesigenic dyskinesia (PKD) is a rare disorder characterised by brief attacks of chorea, dystonia, or mixed forms precipitated by sudden movement.

Methods

Observational study with a cohort of 14 PKD patients and genetic testing for PRRT2 mutations.

Results

In a series of 14 PKD patients seen in our clinic at the National Hospital of Neurology, Queen Square, from 2012–2017, we noted tics in 11 patients (79%), which stand in stark contrast to the estimated lifetime prevalence of tics estimated to reach 1%.

Conclusions

The two reasons to point out this possible association are the clinical implications and the potential opportunity of a better understanding of shared pathophysiological mechanisms of neuronal hyperexcitability.

Aberrant transcriptional networks in step-wise neurogenesis of paroxysmal kinesigenic dyskinesia-induced pluripotent stem cells

Paroxysmal kinesigenic dyskinesia (PKD) is an episodic movement disorder with autosomal-dominant inheritance and marked variability in clinical manifestations.

Proline-rich transmembrane protein 2 (PRRT2) has been identified as a causative gene of PKD, but the molecular mechanism underlying the pathogenesis of PKD still remains a mystery. The phenotypes and transcriptional patterns of the PKD disease need further clarification. Here, we report the generation and neural differentiation of iPSC lines from two familial PKD patients with c.487C>T (p. Gln163X) and c.573dupT (p. Gly192Trpfs*8) PRRT2 mutations, respectively. Notably, an extremely lower efficiency in neural conversion from PKD-iPSCs than control-iPSCs is observed by a step-wise neural differentiation method of dual inhibition of SMAD signaling. Moreover, we show the high expression level of PRRT2 throughout the human brain and the expression pattern of PRRT2 in other human tissues for the first time. To gain molecular insight into the development of the disease, we conduct global gene expression profiling of PKD cells at four different stages of neural induction and identify altered gene expression patterns, which peculiarly reflect dysregulated neural transcriptome signatures and a differentiation tendency to mesodermal development, in comparison to control-iPSCs. Additionally, functional and signaling pathway analyses indicate significantly different cell fate determination between PKD-iPSCs and control-iPSCs. Together, the establishment of PKD-specific in vitro models and the illustration of transcriptome features in PKD cells would certainly help us with better understanding of the defects in neural conversion as well as further investigations in the pathogenesis of the PKD disease.

PRRT2 mutations lead to neuronal dysfunction and neurodevelopmental defects

Mutations in the proline-rich transmembrane protein 2 (PRRT2) gene cause a wide spectrum of neurological diseases, ranging from paroxysmal kinesigenic dyskinesia (PKD) to mental retardation and epilepsy. Previously, seven PKD-related PRRT2 heterozygous mutations were identified in the Taiwanese population: P91QfsX, E199X, S202HfsX, R217PfsX, R217EfsX, R240X and R308C. This study aimed to investigate the disease-causing mechanisms of these PRRT2 mutations. We first documented that Prrt2 was localized at the pre- and post-synaptic membranes with a close spatial association with SNAP25 by synaptic membrane fractionation and immunostaining of the rat neurons. Our results then revealed that the six truncating Prrt2 mutants were accumulated in the cytoplasm and thus failed to target to the cell membrane; the R308C missense mutant had significantly reduced protein expression, suggesting loss-of function effects generated by these mutations. Using in utero electroporation of shRNA into cortical neurons, we further found that knocking down Prrt2 expression in vivo resulted in a delay in neuronal migration during embryonic development and a marked decrease in synaptic density after birth. These pathologic effects and novel disease-causing mechanisms may contribute to the severe clinical symptoms in PRRT2–related diseases.

Proline-rich transmembrane protein 2-negative paroxysmal kinesigenic dyskinesia: Clinical and genetic analyses of 163 patients

BACKGROUND

Paroxysmal kinesigenic dyskinesia is the most common type of paroxysmal dyskinesia. Approximately half of the cases of paroxysmal kinesigenic dyskinesia worldwide are attributable to proline-rich transmembrane protein 2 mutations.

OBJECTIVE

The objective of this study was to investigate potential causative genes and clinical characteristics in proline-rich transmembrane protein 2-negative patients with paroxysmal kinesigenic dyskinesia.

METHODS

We analyzed clinical manifestations and performed exome sequencing in a cohort of 163 proline-rich transmembrane protein 2-negative probands, followed by filtering data with a paroxysmal movement disorders gene panel. Sanger sequencing, segregation analysis, and phenotypic reevaluation were used to substantiate the findings.

RESULTS

The clinical characteristics of the enrolled 163 probands were summarized. A total of 39 heterozygous variants were identified, of which 33 were classified as benign, likely benign, and uncertain significance. The remaining 6 variants (3 novel, 3 documented) were pathogenic and likely pathogenic. Of these, 3 were de novo (potassium calcium-activated channel subfamily M alpha 1, c.1534A>G; solute carrier family 2 member 1, c.418G>A; sodium voltage-gated channel alpha subunit 8, c.3640G>A) in 3 sporadic individuals, respectively. The other 3 (paroxysmal nonkinesiogenic dyskinesia protein, c.956dupA; potassium voltage-gated channel subfamily A member 1, c.765C>A; Dishevelled, Egl-10, and Pleckstrin domain containing 5, c.3311C>T) cosegregated in 3 families. All 6 cases presented with typical paroxysmal kinesigenic dyskinesia characteristics, except for the Dishevelled, Egl-10, and Pleckstrin domain containing 5 family, where the proband's mother had abnormal discharges in her temporal lobes in addition to paroxysmal kinesigenic dyskinesia episodes.

CONCLUSIONS

Our findings extend the genotypic spectrum of paroxysmal kinesigenic dyskinesia and establish the associations between paroxysmal kinesigenic dyskinesia and genes classically related to other paroxysmal movement disorders. De novo variants might be a cause of sporadic paroxysmal kinesigenic dyskinesia. © 2018 International Parkinson and Movement Disorder Society.

Abnormal Somatosensory Synchronization in Patients With Paroxysmal Kinesigenic Dyskinesia: A Magnetoencephalographic Study

Paroxysmal kinesigenic dyskinesia (PKD) is a rare group of hyperkinetic movement disorders characterized by brief attacks of choreoathetosis or dystonia. To clarify the alterations of the functional connectivity within the somatosensory network in PKD patients, magnetoencephalographic (MEG) responses to paired median-nerve electrical stimulation were recorded in 10 PKD patients treated by carbamazepine or oxcarbamazepine and 22 age-matched controls. In patients, MEG recordings were obtained during drug-on and -off periods. Source-based functional connectivity analysis was performed between contralateral primary (cSI) and secondary (cSII), and ipsilateral secondary (iSII) somatosensory areas. During drug-off periods, patients with PKD demonstrated decreased cSI-iSII and increased cSII-iSII somatosensory connectivity at theta band. Drug-on periods lowered the functional connectivity in cSI-cSII at alpha and beta bands and in cSII-iSII at theta band compared with the drug-off periods. We suggest that altered theta functional connectivity in cSI-iSII and cSII-iSII could be the neurophysiological signatures in PKD.

A Novel Truncation Mutation of the PRRT2 Gene Resulting in a 16-Amino-Acid Protein Causes Self-inducible Paroxysmal Kinesigenic Dyskinesia

Paroxysmal kinesigenic dyskinesia (PKD) is a sporadic or autosomal-dominant, hereditary disorder characterized by brief, recurrent attacks of involuntary movements triggered by sudden, voluntary movement that generally develops during childhood and adolescence and is typically treated with carbamazepine. The proline-rich transmembrane protein 2 (PRRT2) gene contains 4 exons that encode 340 amino acids as the major isoform, and recent research has identified PRRT2 as the primary causative gene in PKD, benign familial infantile epilepsy (BFIE), and infantile convulsions with PKD (PKD/IC). Here, the authors report the phenotype of a family with a novel p.E16X (c.46G>T) nonsense mutation of the PRRT2 gene that lacked almost a full allele. In this family, none of the individuals in the pedigree exhibited evidence of cognitive impairment: the elder brother had PKD/IC with migraine; the younger brother had PKD with ataxia; the father had PKD; both siblings experienced a sensory aura; and all 3 had a history of febrile seizures. This is the first report of a short nonsense mutation in PRRT2 and indicates that the manifestations of the disease, including other mutations to date, can be explained by haploinsufficiency and that 1 intact PRRT2 allele can allow normal cognitive development.