A deformity, dysmorphism, or dysmorphic feature is a major difference in the shape of the body a body part, or a body organ (internal or external) compared to the average shape for the part in question.Deformity may arise from numerous causes:
A genetic mutation
Damage to the fetus or uterus
Complications at birth
A growth or hormone disorder
Reconstructive surgery following a severe injury e.g. burn injury.
Arthritis and other Rheumatoid disorders
Irish Mythology includes the Fomorians, who are almost without exception described as being deformed, possessing only one of what most have two of (eyes, arms, leg, etc.) or having larger than normal limbs. Other mythological creatures may have been created due to a deformative syndrome also, for instance, descriptions of mermaids may be related to the symptoms of sirenomelia.Deformity can occur in non-humans, as well. Frogs can be mutated due to Ribeiroia (Trematoda) infection.It is important to note that in many cases, deformed indivi
Source:
http://en.wikipedia.org/wiki/Deformity