Myotonia congenita (MC), paramyotonia congenita (PC) and sodium channel 
myotonias(SCM) were belonged to Non-dystrophic myotonias, in which muscle 
relaxation is delayed after voluntary or evoked contraction. These diseases can 
not be simply distinguished only based on symptoms and signs but also on 
genetics: more than 100 mutations in the CLCN1 gene have been associated with 
MC, while at least 20 mutations in the SCN4A gene have been associated with PC 
and SCM. Most of these genetics studies have been conducted outside China, only 
several MC, PC, and SCM families accepted gene scan were reported in China. 
Therefore we analyzed genetic mutations in CLCN1 and SCN4A in 10 Chinese 
families clinically diagnosed with Non-dystrophic myotonias. Our result revealed 
12 potential disease-causing mutations(3 mutations were novel) that were present 
in the probands and affected family members. We also reviewed all available 
literature on mutations linked to these 3 disease in Chinese populations. Our 
results may help identify genetic determinants as well as clarify 
genotype-phenotype relationships.