Channelopathy linked to epilepsy and paroxysmal dyskinesia

State-dependent inhibition of BK channels by the opioid agonist loperamide

Large-conductance Ca²⁺-activated K⁺ (BK) channels control a range of physiological functions, and their dysfunction is linked to human disease. We have found that the widely used drug loperamide (LOP) can inhibit activity of BK channels composed of either α-subunits (BKα channels) or α-subunits plus the auxiliary γ1-subunit (BKα/γ1 channels), and here we analyze the molecular mechanism of LOP action. LOP applied at the cytosolic side of the membrane rapidly and reversibly inhibited BK current, an effect that appeared as a decay in voltage-activated BK currents. The apparent affinity for LOP decreased with hyperpolarization in a manner consistent with LOP behaving as an inhibitor of open, activated channels. Increasing LOP concentration reduced the half-maximal activation voltage, consistent with relative stabilization of the LOP-inhibited open state. Single-channel recordings revealed that LOP did not reduce unitary BK channel current, but instead decreased BK channel open probability and mean open times. LOP elicited use-dependent inhibition, in which trains of brief depolarizing steps lead to accumulated reduction of BK current, whereas single brief depolarizing steps do not. The principal effects of LOP on BK channel gating are described by a mechanism in which LOP acts as a state-dependent pore blocker. Our results suggest that therapeutic doses of LOP may act in part by inhibiting K⁺ efflux through intestinal BK channels.

FDG PET brain scan demonstrated glucose hypometabolism of bilateral caudate nuclei and putamina in a patient with chorea-acanthocytosis

Chorea-acanthocytosis is 1 type of neuroacanthocytosis that is a group of rare, hereditary neurodegenerative disorders. We presented a brain FDG PET finding of a 31-year-old woman with chorea-acanthocytosis. The images demonstrated significant hypometabolism in bilateral caudate nuclei and putamina. The finding of FDG PET is more prominent than that of MRI. Another interesting observation is the mildly increased FDG uptake in pituitary gland, although its relationship with the disease is unclear.

Exacerbation of idiopathic paroxysmal kinesigenic dyskinesia in remission state caused by secondary hypoparathyroidism with hypocalcemia after thyroidectomy: evidence for ion channelopathy

Most reported cases of paroxysmal kinesigenic dyskinesia (PKD) are idiopathic or familial; however, hypoparathyroidism is another unusual cause of secondary PKD. The pathomechanism of PKD remains poorly understood, and the association between idiopathic and secondary PKD remains an enigma, and has yet to be clearly elucidated. We recently encountered a patient with idiopathic PKD whose symptoms were aggravated by secondary hypoparathyroidism with hypocalcemia after having undergone a thyroidectomy. The patient's paroxysms were ameliorated by the normalization of serum calcium levels. The results discussed herein may provide support for the hypothesis that PKD is associated with neuronal ion regulation.

Neuroacanthocytosis and carbamazepine responsive paroxysmal dyskinesias

Neuroacanthocytosis (NA) comprises a genetically heterogeneous group of disorders characterized by dysfunction of the erythrocyte membrane, presenting with acanthocytes and several neurological manifestations. We report the case of a 42-year-old woman with NA who in addition had episodes consistent with paroxysmal dyskinesias. She was diagnosed with NA featuring mild chorea, weakness of the right lower extremity and myoclonic jerks. However, one year after onset she presented attacks of paroxysmal abnormal movements, consistent with paroxysmal kinesigenic dyskinesias. Carbamazepine markedly reduced the frequency and severity of the attacks. Our case illustrates that paroxysmal dyskinesias can be a hitherto unrecognized manifestation of neuroacanthocytosis responsive to carbamazepine.