• ALS

First, how genetic is amyotrophic lateral sclerosis (ALS)? We know that there are clear ‘Mendelian’ forms of the disease where the classic Mendelian rules of inheritance apply, and several first-degree and second-degree relatives are affected by the disease. Prospective population-based registries show that the rate of this Mendelian form of ALS is about 5% (and not 10% as most often is assumed).1 The far majority of patients, therefore, cannot be classified as such, but twin studies in ALS have shown that genetics explain about 61% of liability in ALS, suggesting that a substantial genetic contribution is available for discovery, even in patients with no family history.2 Also, patients with ‘sporadic’ ALS show mutations in major ALS genes.

In their JNNP manuscript, Zou et al 3 very elegantly describe the genetic epidemiology of sporadic and ‘familial’ ALS, applying a clear definition for familial versus sporadic disease.4 Using guidelines for meta-analyses …