The human skeleton is living tissue that is either growing or being renewed. Our understanding of the pathogenesis of bone disorders has progressed considerably over the past 37 years. A large number of genetic and developmental disorders affect the skeleton. Rare bone diseases account for 5% of all birth defects. The skeletal dysplasias are inherited in an autosomal recessive, autosomal dominant, X-linked recessive, and X-linked dominant, and Y-linked manner.