Mitochondrial DNA variant spectrum and the association with chronic tic disorders.

BACKGROUND AND PURPOSE: Tic disorders (TDs) are childhood onset neuropsychiatric disorders characterized by single or multiple sudden, rapid, recurrent, and motor tics and/or vocal tics. Several nuclear genes that are involved in mitochondrial functions suggest a potential role of mitochondria in TDs. METHODS: To evaluate the association of mitochondrial DNA (mtDNA) variants with TDs, we screened the whole mitochondrial genomes in 493 TD patients and 109 age- and sex-matched healthy controls using next generation sequencing technology. RESULTS: A total of 1918 mtDNA variants including 1220 variants in patients only, 154 variants in controls only, and 544 variants shared by both cases and controls were identified. We found a higher number of overall mtDNA variants in TD patients (p = 0.00028). The variant density in MT-ATP6/8 and MT-CYB coding regions showed a significant difference between TD patients and controls (p = 0.0025 and p = 0.003, respectively). Furthermore, we observed a significant association of 15 common variants with TD based on an additive model, including m.14766C > T, m.14783 T > C, m.14905G > A, and m.15301G > A in MT-CYB; m.4769A > G, m.10398A > G, m.12705C > T, and m.12850A > G in MT-ND genes; m.7028C > T in MT-CO1; m.8701A > G in MT-ATP6; two variants with m.16223C > T, m.5580 T > C in noncoding regions; and three rRNA variants with m.1438A > G and m.750A > G in RNR1, and m.2352 T > C in RNR2. CONCLUSIONS: Our data provide evidence of mtDNA variants associated with TDs. The accumulation of the heteroplasmic levels may increase the risk of TDs. Replication studies with larger samples are necessary to understand the pathogenesis of TDs.

Genetic Knockout of TRPM2 Increases Neuronal Excitability of Hippocampal Neurons by Inhibiting Kv7 Channel in Epilepsy.

Epilepsy is a chronic brain disease that makes serious cognitive and motor retardation. Ion channels affect the occurrence of epilepsy in various ways, but the mechanisms have not yet been fully elucidated. Transient receptor potential melastain2 (TRPM2) ion channel is a non-selective cationic channel that can permeate Ca2+ and critical for epilepsy. Here, TRPM2 gene knockout mice were used to generate a chronic kindling epilepsy model by PTZ administration in mice. We found that TRPM2 knockout mice were more susceptible to epilepsy than WT mice. Furthermore, the neuronal excitability in the hippocampal CA1 region of TRPM2 knockout mice was significantly increased. Compared with WT group, there were no significant differences in the input resistance and after hyperpolarization of CA1 neurons in TRPM2 knockout mice. Firing adaptation rate of hippocampal CA1 pyramidal neurons of TRPM2 knockout mice was lower than that of WT mice. We also found that activation of Kv7 channel by retigabine reduced the firing frequency of action potential in the hippocampal pyramidal neurons of TRPM2 knockout mice. However, inhibiting Kv7 channel increased the firing frequency of action potential in hippocampal pyramidal neurons of WT mice. The data suggest that activation of Kv7 channel can effectively reduce epileptic seizures in TRPM2 knockout mice. We conclude that genetic knockout of TRPM2 in hippocampal CA1 pyramidal neurons may increase neuronal excitability by inhibiting Kv7 channel, affecting the susceptibility to epilepsy. These findings may provide a potential therapeutic target for epilepsy.

Changes of Cytokines in Children With Tic Disorder.

Tic disorder (TD) is a common childhood-onset disease associated with abnormal development of brain networks involved in the motor and sensory processing. The underlying pathophysiological mechanisms in TD are still unclear. An involvement of immune mechanisms in its pathophysiology has been proposed. This study investigates the association between the changes of cytokines and the etiology and development of TD. Different expressions of cytokines in a larger number of samples in our study may provide new insights to the field. The levels of cytokines (IL-2, IL-4, IL-6, IL-10, TNF-α, and IFN-γ) were evaluated in 1,724 patients who were clinically diagnosed with TD from 1 to 17.5 years old and 550 were from 6 months to 14.5 years old in the control group. We assessed the levels of cytokines according to the patient's medication status and the severity of the disease. Of the cytokines we investigated, the serum IL-6 concentration of children with TD was significantly higher than that of the control group, while the levels of other cytokines were lower in TD patients. In the patient group whose YTGSS score ranged from 1 to 9, the IL-4, IL-10, and IFN-γ levels increased in medication group compared to unmedication group. Our data suggested that the cytokines (IL-2, IL-4, IL-6, IL-10, TNF-α, and IFN-γ) may play an important role in the etiology and the severity in TD. Whether drug intervention in the early stage of tic disorder has a better effect on children needs further research.