Congenital erythropoietic porphyria, or Günther disease, is a form of erythropoietic porphyria characterized by very severe and mutilating photodermatosis.

Osteopenia is a term to define bone density that is not normal but also not as low as osteoporosis. By definition from the World Health Organization osteopenia is defined by bone densitometry as a T score -1 to -2.5.