Xeroderma pigmentosum (XP) is a very rare skin disorder where a person is highly sensitive to sunlight (photosensitive), has premature skin aging and is prone to developing skin cancers. This is caused by a cellular hypersensitivity to ultraviolet (UV) light as a result of a defect in the DNA repair system.
Xeroderma pigmentosum is an autosomally recessive inherited disease, which means that you have inherited two recessive xeroderma pigmentosum genes (one from each parent). If your parents are only carriers of the xeroderma pigmentosum trait (each have one xeroderma pigmentosum gene and one normal gene), they will not show signs or symptoms of the disease. By having the two xeroderma pigmentosum genes this causes you to have an extreme sensitivity to UV light and as a result experience a range of signs and symptoms of xeroderma pigmentosum. At least seven different gene abnormalities or complementation groups have been described in different families (XPA to XPG) resulting in varying disease severity.
Essentially, the signs and symptoms of xeroderma pigmentosum are a result of an impaired DNA repair system. In people who do not have xeroderma pigmentosum, cell damage from UV light is mended by the DNA repair system. However, people with xeroderma pigmentosum have a defect in this repair system and any damaged cells from UV light remain unrepaired, leading to cancerous cells or cell death.
Couples who are each carriers of the xeroderma pigmentosum trait are at greater risk of producing a child with xeroderma pigmentosum. Parents already with a child with xeroderma pigmentosum have a 1 in 4 chance of having another child with xeroderma pigmentosum.
Xeroderma pigmentosum occurs worldwide and affects people of all races. Males and females alike can have the condition.
The disease usually progresses through 3 stages. The first stage occurs around 6 months after birth (skin appears normal at birth) with the following signs:
- Areas exposed to the sun such as the face show a reddening of the skin with scaling and freckling. Irregular dark spots may also begin to appear.
- These skin changes progress tthe neck and lower legs. In severe cases the trunk may be involved.
- Over the winter months these changes may diminish.
Continued sun exposure will lead to the second stage, which is characterised by poikiloderma. This is where there are irregular patches of lightened or darkened skin, a spider web-like collection of blood spots and vessels are seen through the skin, and there is thinning of the skin.
The third stage is the development of solar keratoses and skin cancers. These may occur as early as age 4-5 years and are more prevalent in sun-exposed areas such as the face. The common skin cancers, basal cell carcinoma, squamous cell carcinoma, and melanoma, occur significantly more often in people with xeroderma pigmentosum. Other complications, including eye and neurological problems are also apparent in patients with xeroderma pigmentosum.
Eye problems occur in nearly 80% of xeroderma pigmentosum patients.
- Eyes become painfully sensitive to the sun (photophobia).
- Eyes easily irritated, bloodshot and clouded. Conjunctivitis may occur.
- Non-cancerous and cancerous growths on the eyes may occur.
Neurological problems occur in about 20% of xeroderma pigmentosum patients.
- These can be mild or severe and include spasticity, poor coordination, developmental delay, deafness, and short stature.
- May develop in late childhood or adolescence. Once they do occur they tend to worsen over time.
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