POLR1A and nervous system disorder: However, ∼60% of all known disease associated genes are expressed in fibroblasts, and this biological source has shown diagnostic utility in patient groups with rare diseases, including neurological diseases.68,69 In addition, fibroblasts have over many years been proven to be a valuable study material in rare neurological diseases, as recently illustrated.70 Our initial studies of the cellular consequences of POLR1A dysfunction provide information that is valuable for further studies.