One advancement has come from genome-wide association studies that identified hemizygous microdeletions and microduplications termed copy-number variants (CNVs), which confer high risk of these disorders.1 The 15q13.3 hemizygous microdeletion increases the risk of intellectual disability, epilepsy, autism spectrum disorder and schizophrenia 10-fold or more.2, 3, 4, 5 The microdeletion encompasses a region of ~1.5 MB from break-point (BP) 4 to BP5, with seven genes; MTMR10; FAN1; TRPM1; miR-211; KLF13; OTUD7A; and CHRNA7 (OMIM #612001). The gene discussed is FAN1; the disease is Intellectual disability.