Some causes of short stature are well-understood and can be corrected, but most are subjects of ongoing research. In some cases, individuals with growth defects are extremely short and have normal body proportions. In other cases, they have abnormal body proportions. Among those with abnormal body proportions, some have arms and legs that are very short while the torso is more nearly normal size. Achondroplasia is the most common growth defect of this type.
Achondroplasia is a genetic disorder of bone growth that is evident at birth.
It affects about one in every 20,000 births and it occurs in all races and in both sexes. Its depiction in ancient Egyptian art makes it one of the oldest recorded birth defects. During fetal development and childhood, cartilage normally develops into bone, except in a few places, such as the nose and the ears. The rate at which cartilage cells in the growth plates of the long bones turn into bone is slow, leading to short bones and reduced height. A child with achondroplasia has a relatively normal torso and short arms and legs.