achondroplasia /ākon′drōplā″zhə/ [Gk, a + chondros, without cartilage, plassein, to form] , a rare disorder of the growth of cartilage in the epiphyses of the long bones and skull. It results in premature ossification, permanent limitation of skeletal development, and dwarfism typified by a protruding forehead and short, thick arms and legs on a normal trunk. Onset is in fetal life and the diagnosis can be made on prenatal ultrasound. It is inherited as an autosomal-dominant gene with most cases occurring as a sporadic mutation (affecting a fibroblast growth factor receptor). The majority of affected individuals die during gestation or the first year of life. Those who survive have relatively normal longevity. Also called chondrodystrophy, fetal rickets.