De novo FUS mutations in 2 Korean patients with sporadic amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder. Approximately 5% of ALS patients are familial (fALS) cases, and the remaining 95% are apparently sporadic (sALS) cases. To date, a number of genes have been discovered as associated with ALS, but the genetic background of sALS is not yet fully understood. The occurrence of de novo mutations in ALS genes might be an explanation for sALS, but reduced penetrance could be an alternative theory. Previously, we screened mutations in 5 ALS genes including SOD1 and FUS in 9 fALS and 249 sALS patients and found a total of 15 patients with either SOD1 (7 fALS and 3 sALS) or FUS (1 fALS and 4 sALS) mutations. Interestingly, only 1 fALS patient had the FUS mutation, whereas 4 sALS patients had mutations in this gene. To determine if the FUS mutations in sALS were de novo, we performed genetic analysis on 2 sALS patients with living parents. Genetic analysis confirmed that 2 FUS mutations, including the c.1483C>T (p.Arg495*) and the c.1509_1510delAG (p.Gly504Trpfs*12) mutations, were found only in the patients and not in their parents, confirming the denovo occurrence of these mutations. These findings support the notion that de novo mutations are responsible for a certain proportion of sALS.