Ryan M, et al. - Researchers examined the contribution of genetic factors to the variation in lifetime risk of developing amyotrophic lateral sclerosis via performing a population-based parent-offspring heritability study including a total of 1,123 incident cases of amyotrophic lateral sclerosis (ALS), diagnosed according to the El Escorial criteria and recorded on the Irish ALS register. Exclusion of 92 individuals (non-Irish parental origin [n = 86] and familial ALS [n = 6]) left 1,117 patients for the final analysis. As per the analysis, genetic factors are related to half of the variation in the risk of developing amyotrophic lateral sclerosis overall and close to 40% in a population devoid of known gene mutations. In female-specific pairings, they observed higher heritability estimates. This indicates the transmission of the C9orf72 repeat expansion in a sex-dependent manner. Findings thereby suggest an approximately equal contribution of inherited and noninherited factors toward amyotrophic lateral sclerosis. Even in a population devoid of known gene mutations, high heritability of amyotrophic lateral sclerosis was observed, supporting ongoing efforts to identify causative genes.