Xeroderma Pigmentosum: Causes, Symptoms and Treatment

What is Xeroderma Pigmentosum?

Xeroderma Pigmentosum (abbreviated XP) is a rare, genetically inherited disorder characterized by extreme sensitivity of the skin to ultraviolet (UV) radiation. The condition arises from defects in the DNA repair machinery, specifically the nucleotide excision repair (NER) pathway, which is responsible for correcting UV-induced damage to the genetic material. XP affects approximately 1 in 1,000,000 individuals in Europe and North America, but occurs more frequently in certain regions such as Japan and the Middle East.

Causes

Xeroderma Pigmentosum is inherited in an autosomal recessive pattern, meaning a child must inherit one defective gene copy from each parent to develop the condition. At least eight distinct genetic subtypes have been identified (XP-A through XP-G and XP-V), each involving different proteins in the NER pathway. These proteins are normally responsible for recognizing and removing UV-induced DNA lesions known as pyrimidine dimers. When these repair mechanisms fail, DNA damage accumulates and can lead to mutations that drive cancer development.

Symptoms

Symptoms typically appear in early childhood and primarily affect the skin, eyes, and in some cases, the nervous system.

Skin Symptoms

• Severe sunburn and blistering after only minimal sun exposure
• Freckles and pigmented spots (lentigines) on the face and arms, even in areas not directly exposed to sunlight
• Dry, scaly skin (xeroderma)
• Premature skin aging (photoaging)
• Dramatically elevated risk of skin cancer (basal cell carcinoma, squamous cell carcinoma, malignant melanoma) -- up to 10,000 times higher than in the general population

Eye Symptoms

• Sensitivity to light (photophobia)
• Inflammation of the eyelids and conjunctiva
• Corneal clouding
• Increased risk of eye tumors

Neurological Symptoms

• In certain XP subtypes (particularly XP-A and XP-D): progressive neurological deterioration including hearing loss, impaired coordination, and cognitive decline
• Possible development of De Sanctis-Cacchione syndrome, a severe form with significant neurological involvement

Diagnosis

Diagnosis of Xeroderma Pigmentosum is based on a combination of approaches:

• Clinical evaluation: Assessment of characteristic skin changes and patient history
• Cell biology testing: Laboratory measurement of DNA repair capacity in skin cells (fibroblasts) after UV irradiation
• Genetic testing: Molecular genetic analysis to identify the specific complementation group affected
• Prenatal diagnosis: Available for families at risk through genetic testing of fetal cells

Treatment

There is currently no cure for Xeroderma Pigmentosum. Management focuses on rigorous protection from UV radiation and early detection and treatment of skin tumors.

UV Protection

• Strict and comprehensive avoidance of both natural sunlight and artificial UV sources (e.g., fluorescent lighting)
• Wearing protective clothing, high-factor sunscreens (SPF 50+), and UV-blocking eyewear
• Application of UV-protective window film in homes and schools

Dermatological and Ophthalmological Monitoring

• Regular dermatological examinations for early detection of skin tumors
• Surgical removal of skin cancers
• Regular ophthalmological follow-up

Medical Therapy

• Topical application of DNA repair enzymes (e.g., T4 endonuclease V in liposome-based preparations) as a supplementary measure
• Isotretinoin (a vitamin A derivative) may be used in selected cases to reduce the development of new skin tumors

Psychosocial Support

Because Xeroderma Pigmentosum is a lifelong condition that places significant restrictions on daily life, psychosocial support for patients and their families is an essential component of comprehensive care.

Prognosis

Life expectancy for individuals with Xeroderma Pigmentosum depends greatly on disease severity, the presence of neurological involvement, and the consistency of UV protection measures. With rigorous photoprotection and regular medical surveillance, many patients can lead largely normal lives. Without adequate protection, multiple skin cancers can develop as early as childhood.

References

1. Kraemer, K. H. et al. (2007): Xeroderma Pigmentosum. In: GeneReviews, NCBI Bookshelf. National Center for Biotechnology Information.
2. Lehmann, A. R., McGibbon, D., Stefanini, M. (2011): Xeroderma Pigmentosum. Orphanet Journal of Rare Diseases, 6:70.
3. World Health Organization (WHO): Ultraviolet Radiation and Human Health. WHO Fact Sheet. Geneva.