Dysmelia

Dysmelia (from Gr. δυσ- dys, "bad" + μέλ|ος mél|os, "limb" + Eng. suff. -ia) is a congenital disorder referring to the limbs.

Types
Dysmelia can refer to
 * missing (aplasia) limbs: amelia, oligodactyly, congenital amputation
 * malformation of limbs: ectrodactyly, phocomelia, meromelia, syndactyly, brachydactyly, club foot
 * too many limbs: polymelia, polydactyly, polysyndactyly

Occurrence rate
Birth defects involving limbs occur in 1 per 1000.

Causes
Dysmelia can be caused by
 * inheritance of abnormal genes, e.g. polydactyly, ectrodactyly or brachydactyly, symptoms of deformed limbs then often occur in combination with other symptoms (syndromes)
 * external causes during pregnancy (thus not inherited), e.g. via amniotic band syndrome
 * teratogenic drugs (e.g. thalidomide, which causes phocomelia) or environmental chemicals
 * ionizing radiation (nuclear weapons, radioiodine, radiation therapy)
 * infections
 * metabolic imbalance