In another study, heterozygous mutations in NOTCH2, such as the nonsense mutation c.7198C>T in HCS06 and mutation c.6383delG in HCS02, were identified as the cause of Hajdu–Cheney syndrome, which affects several organ systems, leading to severe osteoporosis and other abnormalities [17]. The gene discussed is NOTCH2; the disease is osteoporosis.