Erythema multiforme (EM) is the name applied to a group of hypersensitivity disorders, affecting mostly children and young adults, and characterized by symmetric red, patchy lesions, primarily on the arms and legs. The cause is unknown, but EM fre...

Osteopetrosis may be inherited as either a dominant or recessive trait and is marked by increased bone density, brittle bones, and, in some cases, skeletal abnormalities. Although symptoms may not initially be apparent in people with mild forms of...