A paralysis periodica paramyotonia congenital pedigree: clinic and molecular genetic studies / 中华神经科杂志

ABSTRACT

Objective To report clinical symptoms of a Chinese pedigree of familial paramyotonia congenital (PMC) with progressive myopathy (PM), and investigate the mutations of hot spots in the adult skeletal muscle sodium channel α-subunit (SCN4A). Methods The medical history and clinical phenotype of the patients from this large family with PMC were collected. Insertional and spontaneous activity were recorded by routine electromyograph (EMG), and the exercise test (ET) and cool water test were also performed on some patients during episodes. The mutations of SCN4A were screened by PCR-SSCP and DNA sequencing in affected and unaffected members. Results The family is a four-generation kindred with 15 members affected by severe, homogeneous paralysis periodiea paramyotoniea pheuotype. The onset was early, and almost all patients developed severe progressive myopathy by middle age. Routine EMG shows myotonia discharge in all affected subjects. The compound remarkably motor action potential (CMAP) decreased more than 40% after ET with greater decreases in cool water test than in ET. The mutation screening study revealed a missense mutation (Met1592Val) in SCN4A in patients. Conclusions Autosomal dominant inheritance pattern with complete penetrance was observed in this family. The phenotype is in accord with that reported in other ethnic populations with more severe symptoms. The ET and cool water tests may be used as an easy and reliable diagnostic method. Our research supports that periodic paralysis and paramyotonia can be caused by the same mutation in SCN4A. Mutation Met1592Val is a hotspot for mutation screening in patients with PMC accompanied by PM in the Chinese population.