Talks on rare diseases in the field of neurology often start with a statement like this: “About 80% of all rare diseases have a neurologic manifestation and about 80% of those are genetic in origin.” Although these numbers probably represent more of an estimate than well-documented evidence, rapidly advancing and cost-effective sequencing technologies have led to the quickly growing identification of patients with hereditary neurological diseases. Although the importance of genetics for diagnosis and genetic counseling is undisputed, the recent development of first genetargeted therapies entering clinical trial1,2 is adding an important new layer to the (re-)consideration of genetic testing in neurology. However, establishing accurate genotype– phenotype and genotype–treatment relationships requires large sample sizes. Systematic reviews can serve as instruments to combine information from several small samples, but unfortunately, this is often complicated by inconsistent and incomplete reporting of clinical and genetic data across studies. Thus, large multicenter approaches are necessary to systematically and uniformly characterize patients with genetic neurologic conditions and to eventually establish sizable clinical trial-ready cohorts.