Xeroderma pigmentosum
| Xeroderma pigmentosum | |
|---|---|
 |
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| An eight-year-old girl from Guatemala with xeroderma pigmentosum | |
| Classification and external resources | |
| Specialty | medical genetics |
| ICD-10 | Q82.1 |
| ICD-9-CM | 757.33 |
| OMIM | 278700 |
| DiseasesDB | 14198 |
| MedlinePlus | 001467 |
| eMedicine | derm/462 neuro/399 |
| Patient UK | Xeroderma pigmentosum |
| MeSH | D014983 |
| GeneReviews | |
| Orphanet | 910 |
Xeroderma pigmentosum (XP) is a rare autosomal recessive genetic disorder of DNA repair in which the ability to repair damage caused by ultraviolet (UV) light is deficient. In extreme cases, all exposure to sunlight must be forbidden, no matter how small; as such, individuals with the disease are often colloquially referred to as "Moon child". Multiple basal cell carcinomas (basaliomas) and other skin malignancies frequently occur at a young age in those with XP; metastatic malignant melanoma and squamous cell carcinoma are the two most common causes of death in XP victims. This disease is present in both genders and in all races, with an incidence of 1:250,000 in the United States. XP is roughly six times more common in Japanese people than in other groups.
Normally, damage to DNA in epidermal cells occurs during exposure to UV light. The absorption of the high-energy light leads to the formation of pyrimidine dimers, namely cyclobutane-pyrimidine dimers and pyrimidine-6-4-pyrimidone photoproducts. In a healthy, normal human being, the damage is first excised by endonucleases. DNA polymerase then repairs the missing sequence, and ligase "seals" the transaction. This process is known as nucleotide excision repair.
One of the most frequent defects in xeroderma pigmentosum is an autosomal recessive genetic defect in which nucleotide excision repair (NER) enzymes are mutated, leading to a reduction in or elimination of NER. If left unchecked, damage caused by ultraviolet light can cause mutations in individual cell's DNA. The causes of the neurological abnormalities are poorly understood and are not connected with exposure to ultraviolet light. The most current theories suggest that oxidative DNA damage is generated during normal metabolism in the central nervous system, and that some types of this damage must be repaired by NER
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