In a survey of individuals with dwarfism in which 148 cases of typical achondroplasia were diagnosed, an additional group of 13 individuals was found to have an allied condition that was clearly a distinct entity. This is hypochondroplasia, a chondrodystrophy with roentgenographic changes similar to but milder than those of achondroplasia and without involvement of the skull. Hypochondroplasia is a heritable condition with autosomal dominant transmission. The diagnosis can only be established by roentgenographic examination.
Walker BA, Murdoch JL, McKusick VA, Langer LO, Beals RK. Hypochondroplasia. Am J Dis Child. 1971;122(2):95-104. doi:10.1001/archpedi.1971.02110020029001