This is exemplified by the recent dismissal of HYDIN2 as a driver gene for the head circumference phenotype in 1q21.1 distal CNV: Several atypical 1q21.1 distal deletion and duplication carriers with normal copy number variation of HYDIN2, but still exhibiting the microcephaly or macrocephaly phenotype, were identified (Dougherty et al., 2017). The gene discussed is HYDIN2; the disease is microcephaly.