What are the symptoms? Symptoms occur from early infancy in 50 per cent of affected individuals: Extreme sensitivity to sunlight including severe blistering sunburnsPersistent redness (sunburn) even upon minimal sun exposureMarked freckling in sun-exposed areas in a child under 2 years old. Degrees of pigmentary change of the skin occur including freckling, dryness, premature skin ageing and development of skin cancers in childhood. UV light causes damage to the surface of the eyes including the cornea, conjunctiva and eyelids. Neurological abnormalities occur in approximately 30 per cent of patients and include learning disability (see entry Learning Disability), spasticity (stiffness or tightness of muscle), poor coordination and deafness. XP patients may be of small stature and demonstrate developmental delay. What are the causes? There is a defect in one of seven genes that produce proteins involved in skin repair following UV light induced DNA damage. There are at least eight different subtypes of XP; seven different genes (XP group A-G genes) are affected and an XP variant is also reported. Severity and nature of the disease relates to which gene is affected, although exceptions can occur due to different gene mutations. In general, XP group C, E and F patients (and XP variants) are spared neurological problems, whilst these variably occur in groups A, D and G. How is it diagnosed? The first symptoms of XP typically appear between age 1-2 years old and diagnosis is made based on skin, eye and neurological symptoms. Testing for XP involves measuring activity of DNA repair enzymes in a skin biopsy specimen taken from the upper arm. Once XP is considered a possibility, parents should reduce, if not totally avoid, UV light exposure in their child, as early avoidance can delay the onset of complications. How is it treated? Treatment includes rigorous protection against UV light with sunscreens, wearing of UV-blocking clothing and eyewear, and lifestyle modifications to minimise UV exposure. Patients should be monitored carefully for signs of skin cancers and treated as soon as possible. Pre-cancerous skin growths should be treated early because of their potential to become cancerous. This can involve cryotherapy (freeze-treatment), topical immunomodulators (cream/ointment applied to the affected area to alter the immune system response such as 5-fluorouracil or imiquimod) or surgery. Vitamin D is produced by skin when exposed to UV radiation. Children who are diagnosed with XP early in life are UV-protected and have very low vitamin D levels, making them prone to bone fractures. Supplementation is recommended. Inheritance patterns and prenatal diagnosis Patterns of inheritanceXP is inherited in an autosomal recessive pattern. The parents of an individual with XP will be carriers of a mutation in one of the XP genes. Prenatal diagnosisThis may be offered for families in which the disease-causing mutations have been identified. This can be performed by amniocentesis or chorionic villus sampling. Is there support? . Action for XP (formerly Teddington Trust and XP Support Group) Email: email@example.comWebsite: www.actionforxp.org Action for XP is a Scottish Regulated Charity no. SC045465. They provide practical and emotional support to patients and families affected by Xeroderma Pigmentosum, along with patient information. They aim to raise awareness of XP and to further scientific understanding of the condition. Group details updated August 2022.