Homozygous variations in ACAN lead to SEMD, aggrecan type (SEMDAG) (MIM 612813, autosomal recessive), and heterozygous variation leads to SED, Kimberley type (SEDK) (MIM 608361, autosomal dominant) as well as short stature and advanced bone age, with or without early‐onset osteoarthritis and/or osteochondritis dissecans (MIM 165800, autosomal dominant). The gene discussed is ACAN; the disease is osteochondritis dissecans.