Xeroderma pigmentosum (XP) is a group of rare inherited skin disorders characterized by a heightened reaction to sunlight (photosensitivity) with skin blistering occurring after exposure to the sun. In some cases, pain and blistering may occur immediately after contact with sunlight. Acute sunburn and persistent redness or inflammation of the skin (erythema) are also early symptoms of XP. In most cases, these symptoms may be apparent immediately after birth or occur within the next three years. In other cases, symptoms may not develop until later in childhood or, more rarely, may not be recognized until adulthood. Other symptoms of XP may include discolorations, weakness and fragility, and/or scarring of the skin.
Xeroderma pigmentosum affects the eyes as well as the skin, has been associated with several forms of skin cancer, and, in some cases, may occur along with dwarfism, mental retardation, and/or delayed development.
Several subtypes of XP (i.e., XP complementation groups) have been identified, based upon different defects in the body's ability to repair DNA damaged by ultraviolet light (UV). According to the medical literature, the symptoms and findings associated with the classic form of xeroderma pigmentosum, known as XP, type A (XPA), may also occur in association with the other XP subtypes. These include: XP, type B (XPB); XP, type C (XPC), XP, type D (XPD); XP, type E (XPE); XP, type F (XPF); and XP, type G (XPG). These XP subtypes are transmitted as an autosomal recessive trait. In addition, another subtype of the disorder, known as XP, dominant type, has autosomal dominant inheritance.
In addition to the XP subtypes discussed above, researchers have identified another form of the disorder known as XP, variant type (XP-V). As with the other XP subtypes, symptoms and findings associated with the classic form of XP may also be seen in individuals with XP-V. XP-V cells have a normal or near normal ability to repair UV-induced DNA damage (nucleotide excisional repair), however, they are defective in replicating UV-damaged DNA during the division and reproduction of cells. Although the disorder's mode of inheritance is unknown, most researchers suspect that XP-V is transmitted as an autosomal recessive trait.