About 5% of amyotrophic lateral sclerosis (ALS) cases are known to be familial (fALS) and mutations in SOD1 and other genes are found in more than 20% of fALS patients and in 2%-4% of apparently sporadic ALS (sALS) cases. However, there are few reports on the proportion of fALS and the frequency of mutations in Korean patients with ALS. We screened mutations in the SOD1, FUS, TARDBP, ANG, and OPTN genes in 258 consecutively enrolled Korean patients with ALS from October 2006 to November 2010. The frequency of fALS was estimated to be 3.5% (9/258), and mutations were identified in 88.9% (8/9) of fALS patients but only in 2.8% (7/249) of sALS patients. Seven fALS and 3 sALS patients had mutations in SOD1 gene while all the others had FUS gene. The proportion of fALS was lower than that reported in Caucasian populations but the frequency of SOD1 gene mutations in Korean fALS patients (77.8%, 7/9) was much higher than that reported in other ethnic groups. These findings might suggest that there is an ethnic difference in the proportion of fALS and the genetic background of ALS.
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