Clinical features of thyrotoxic periodic paralysis caused by inwardly rectifying potassium channel 18 gene mutations

Abstract

Objective To report the clinical features and inwardly rectifying potassium channel 18 (KCNJ18) gene mutation in a group of patients with thyrotoxic periodic paralysis (TTP). Methods Fifty-seven TTP cases (55 male and 2 female) were collected in our clinic from July 2002 to October 2011. The KCNJ18 gene was directly sequenced in 57 TTP patients and 50 health Chinese controls through the nested PCR. According to the results of gene screening, the clinical features of KCNJ18 patients and non-KCNJ18 patients were retrospectively summarized and analyzed. Results In 4 male patients with TPP, we found 3 novel heterogeneous mutations (p.Q126X, p.K360T, p.E388K) and 1 reported mutation (p.A200P) in the KCNJ18 gene. The age of onset was 19—25 years old, and the duration ranged from 2 to 8 hours. The 4 patients all presented severe muscle weakness. The attacks of muscle weakness preceded overt symptoms of hyperthyroidism in the 4 patients. Three patients showed recurrent weakness during the 13—28 months follow-up, while the episodic weakness never appeared when patients got euthyroid. Conclusions The mutations in the KCNJ18 gene are responsible for a part of Chinese patients with TPP. The patients with KCNJ18 mutations have a shorter disease course, severer manifestation, and higher prevalence of recurrence as compared with those TPP patients without KCNJ18 mutations. Key words: Thyrotoxicosis; Potassium channels; inwardly rectifying; Hypokalemic periodic paralysis; Hyperthyroidism