Baldassari et al. (2019) have reported a genotype-phenotype relationship and observed a significant difference in the distribution of the age at seizure onset among mild MCDs (mMCD) and FCD patients with somatic variants in PIK3CA, AKT3, RHEB, MTOR, TSC1/2, and SLC35A2 or germline variants in TSC2 or DEPDC5, reflecting a link between the occurrence of these variants and early onset. The gene discussed is RHEB; the disease is Schmid metaphyseal chondrodysplasia.