Xeroderma Pigmentosum

Synonyms

XP

Epidemiology

From about 1 in 500,000 live births in Western Europe to much higher frequencies in Japan and North Africa.

Definition

Group of uncommon genodermatoses with markedly increased light sensitivity and tendency towards developing actinic damage and malignant skin tumours.

Aetiology & Pathogenesis

Autosomal recessive inherited defects in DNA excision repair enzymes. Cells cannot repair UV-induced damage.

Signs & Symptoms

Marked photosensitivity with acute photodermatitis and marked actinic damage, multiple lentigines, including actinic keratoses, squamous cell carcinomas, basal cell carcinomas, malignant melanomas, poikiloderma, skin atrophy. Eyes also suffer UV damage. Some types (DeSanctis-Cacchione syndrome) have neurological findings.

Localisation

Generalised; visible symptoms in UV light-exposed areas.

Classification

Types A-G dependent on type of gene defect.

Laboratory & other workups

Identification of endonuclease and other repair enzyme defects in cultured fibroblasts, DNA sequencing of known genes.

Dermatopathology

According to light induced skin damage and type and stage of tumor.

Course

Reduced life expectancy starting already in the first life decade and depending on defect. Development of multiple malignant skin tumours, especially squamous cell carcinomas and malignant melanomas.

Complications

Development of malignant skin tumours (squamous cell carcinoma, basal cell carcinoma, malignant melanoma) before 20 years of age.

Diagnosis

Clinical findings (photosensitivity, early actinic damage), genetic analysis, family history.

Differential diagnosis

Xeroderma pigmentosum variants with same phenotype, later onset, no genetic defects (pigmented xerodermoid).

Prevention & Therapy

Consequent avoidance of UV exposure. Early use of high-potency broad-spectrum sunscreens, close clinical control, prompt tumour excision. Systemic retinoids for prophylaxis. Vitamin D supplementation.

Special

Genetic counselling.

6.1.2 Xeroderma Pigmentosum