SCN4A Gene Mutations Analysis In Normokalemic Periodic Paralysis Patients

Context Periodic paralysis (PP) is a group of ion channel dysfunction diseases. It is characterized by recurrent flaccid muscle weakness or paralysis attack with or without abnormal serum potassium levels. Depending on serum potassium level, PP is divided into hypokalemic periodic paralysis (HypoKPP), hyperkalemic periodic paralysis (HyperKPP), and normokalemic periodic paralysis (NormoKPP). NormoKPP is a very rare diseases and characterized by flaccid muscle weakness or paralysis repeatedly attacked with normal serum potassium levels. NormoKPP is an autosomal dominant genetic disease involvingα-subunit typeⅣof voltage-gated sodium channel gene (SCN4A), including both familial and sporadic cases. In two types, familial ones are more common in Western countries, whiles sporadic ones are more in China and other Asian countries. 20 kinds of SCN4A gene mutations had been reported between domestic and foreign countries, including 6 mutations related to NormoKPP. It is reported mutations led to NormoKPP located in the exon 12, 13and 24 of SCN4A gene, such as T704M, R675G, R675W, R675H, R675Qand M1592V. Many family or sporadic NormoKPP cases had reported in our country, but it is rarely reported about SCN4A gene mutations causing NormoKPP. NormoKPP has no specific clinical features, so early diagnosis was still difficult. With the development of molecular biology, genetic diagnosis is an important method for diagnosis of NormoKPP.Objective By PCR amplification and DNA sequence analysis, all 24 exons and adjacent introns of the SCN4A gene were detected, in order to obtain the exact gene mutation. Molecular etiology of the NormoKPP provide data to help the diagnosis, treatment and genetic counseling of the NormoKPP patients.Methods Total genomic DNA was extracted from the peripheral blood leukocytes of the patients, their parents and 50 healthy control subjects. Polymerase chain reaction (PCR) and direct DNA sequencing were used to detect SCN4A mutations. Restriction enzyme analysis was used to confirm the pathogenicity of mutation.Results1. One patient detected a heterozygous mutation of SCN4A gene. It was C>T transition at nucleotide 2111 in exon 13, which led to the substitution of a threonine residue with methionine (T704M). The heterozygous mutation was also detected in his father, but not affected. His mother and the healthy control group were not found this mutation;2. Another NormoKPP patients did not find pathogenic mutation;3. Hgal enzyme cut reaction confirmed patient 1 and his father exist the heterozygous mutation C >T;4. Six SCN4A gene polymorphisms were identified, 864 C>T (N288N), 1570 A>G(S524G), 2289 C>T(I763I), 4126 A>G(N1376D), 4539 C>A(I1513I) and 4869 A>G(T1623T). 4 of which has been collected in SNP databases, but 2289 C > T (I763I) and 4539 C > A (I1513I) have not been reported.Conclusions1. In the study, the mutation T704M of SCN4A cause NormoKPP in NormoKPP patients 1 and it is a hot mutations have been reported;2. T704M mutation in the NormoKPP patients may be incomplete penetrance. The penetrance of this mutation has not been reported, which need further study.