Genetic epidemiology of familial ALS in Brazil

Many genes associated with familial forms of the amyotrophic lateral sclerosis (fALS) have been identified in European and North American cohorts. However, little is known about the genetic bases of fALS in Latin America and Brazil, in particular. To address this question, we recruited 107 patients with fALS from 93 unrelated families from Southeastern, Southern, and Northeastern regions of the country. A 3-step diagnostic approach was used: 1) Triplet repeat primed polymerase chain reaction to search for C9orf72 expansions, then 2) fragment digestion to search for the c.166 C>T VAPB variant, and finally, 3) whole exome sequencing for those who tested negative. We identified the genetic cause for fALS in 70% of the families. VAPB and C9orf72 were the most frequent genes (30% and 22%, respectively), followed by SOD1, TARDBP, ANXA11, and FUS. Five novel variants in known ALS genes were found, including the SOD1 Val120Leu and ANXA11 Asp40Tyr, which were seen in 2 unrelated families each. In conclusion, VAPB and then C9orf72 are the genes most commonly related to fALS in Brazil.