Scoliosis even when untreated, with mortality rates similar to the general population. Older beliefs that untreated idiopathic scoliosis necessarily progresses into severe (cardiopulmonary) disability by old age have been refuted by later studies. The many causes of scoliosis include spinal deformities, neuromuscular problems, and inherited diseases or conditions caused by the environment. An estimated 65% of scoliosis cases are idiopathic, about 15% are congenital, and about 10% are secondary to a neuromuscular disease. Idiopathic scoliosis represents a majority of cases, but its causes are largely unknown. Recent studies indicate potential heritability of the disorder. About 38% of variance in scoliosis risk
Supernumerary body part considered to have lost much or all of their original function through evolution. These body parts can be classed as additional to the required functioning of the body. In human anatomy the vermiform appendix is sometimes classed as a vestigial remnant. Prosthesis is an artificial extension that replaces a body part, and cybernetics is the study of computer technology in relation to organisms which can include replacement or additional body parts. Body integrity identity disorder (BIID) is a psychiatric disorder in which a person thinks that they have one or more additional limbs than they should, despite having two arms