Conversely, up to 20% of OI is due to homozygous mutations in genes widely involved in bone homeostasis, namely Wnt Family Member 1 (WNT1) and low-density lipoprotein receptor-related protein 5 (LRP5), and inherited in an autosomal recessive (AR) manner (5–7). The gene discussed is LRP5; the disease is osteogenesis imperfecta.