Xeroderma pigmentosum

Xeroderma pigmentosum

An eight-year-old girl from Guatemala with xeroderma pigmentosum[1]
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
Child suffering from xeroderma pigmentosum in Rukum, Nepal
Xeroderma pigmentosum has an autosomal recessive pattern of inheritance.

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.[2]:574 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".[3] 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[4] are the two most common causes of death in XP victims. This disease involves both sexes and all races, with an incidence of 1:250,000 in the United States.[5] XP is roughly six times more common in Japanese people[4] 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.

Genetics

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.[6] 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[7]

Since DNA repair is under genetic control, it can easily undergo mutations. Many genetic disorders such as xeroderma pigmentosum (XP; MIM 278700) are caused by mutations in genes that repair DNA.[7] If the gene was not repaired correctly it could cause xeroderma pigmentosum in individuals. The autosomal recessive disorder xeroderma pigmentosum or XP has a frequency of 1 in every 250,000 individuals of all races and ethnic groups.[8] Those affected with the autosomal recessive disorder XP are extremely sensitive to UV light produced by the sun and even with a short exposure to it causes dry, flaking skin and pigmented spots that can develop into skin cancer. Individuals with XP are about 1,000 times more likely to develop skin cancer than individuals without the disorder.

The molecular defects in XP cells result in a greatly elevated induction of mutations in sun-exposed skin of affected individuals. This increased mutation frequency probably accounts for the pigmentation changes and the skin cancers. Examination of mutations in the p53 gene in tumors from XP patients reveal p53 mutations characteristic of UV exposure in the majority of tumors[8] As with all genetic disorders, genetic counseling and psychological support is appropriate for the families, to discuss probability of occurrence in future pregnancies, feelings of isolation and concern about career prospects. Although there is no cure for xeroderma pigmentosum, the effects can be minimized by getting protection from the sunlight and if possible early removal of precancerous lesions. The most common fate for individuals with XP is early death from cancer due to the fact that they need to take outstanding measures to protect themselves from the dangers of the UV light. But if there is an absence of neurological problems and are always protected or away from the sunlight, the prognosis is good.

Types

There are seven complementation groups, plus one variant form:

Type Diseases Database OMIM Gene Locus Also known as / description
Type A, I, XPA29877 278700 XPA 9q22.3 Xeroderma pigmentosum group A - the classical form of XP
Type B, II, XPB 29878 133510 XPB 2q21 Xeroderma pigmentosum group B
Type C, III, XPC 29879 278720 XPC 3p25 Xeroderma pigmentosum group C
Type D, IV, XPD 29880 278730 278800 XPD ERCC6 19q13.2-q13.3, 10q11 Xeroderma pigmentosum group D or De Sanctis-Cacchione syndrome (can be considered a subtype of XPD)
Type E, V, XPE 29881 278740 DDB2 11p12-p11 Xeroderma pigmentosum group E
Type F, VI, XPF 29882 278760 ERCC4 16p13.3-p13.13 Xeroderma pigmentosum group F
Type G, VII, XPG 29883 278780 133530 RAD2 ERCC5 13q33 Xeroderma pigmentosum group G and COFS syndrome type 3
Type V, XPV 278750 POLH 6p21.1-p12 Xeroderma pigmentosum variant - these patients suffer from mutation in a gene that codes for a specialized DNA polymerase called polymerase-η (eta). Polymerase-η can replicate over the damage and is needed when cells enter S-phase in the presence of a DNA-replication.

Symptoms

Symptoms include:

Treatment

The most obvious, and often important part of treatment, is avoiding exposure to sunlight. This includes wearing protective clothing and using sunscreen (physical and chemical).[9] Keratoses can also be treated using cryotherapy or fluorouracil.[1]

Prognosis

Fewer than 40% of individuals with the disease survive beyond the age of 20. Some XP victims with less severe cases do manage to live well into their 40s.

In popular culture

These fictional characters have XP:

See also

References

  1. 1 2 Halpern, J.; Hopping, B.; Brostoff, J. (2008). "Photosensitivity, corneal scarring and developmental delay: Xeroderma Pigmentosum in a tropical country". Cases journal 1 (1): 254. doi:10.1186/1757-1626-1-254. PMC 2577106. PMID 18937855.
  2. ↑ James, William; Berger, Timothy; Elston, Dirk (2005). Andrews' Diseases of the Skin: Clinical Dermatology. (10th ed.). Saunders. ISBN 0-7216-2921-0.
  3. ↑ Medical Biochemistry at a Glance. John Wiley & Sons. 28 November 2011. ISBN 1118292405. Retrieved 17 June 2011. Xeroderma pigmentosa is a rare, autosomal recessive disease caused by a defective UV-specific endonuclease. Patients with mutations are unable to repair DNA damage caused by sunlight and have been described as "children of the night."
  4. 1 2 Li, Lei (January 8, 2007). "Chapter 3 Nucleotide Excision Repair". DNA REPAIR, GENETIC INSTABILITY, AND CANCER. World Scientific Publishing. pp. 75–76. ISBN 981-270-014-5.
  5. ↑ Lehmann AR, McGibbon D, Stefanini M (2011). "Xeroderma pigmentosum". Orphanet J Rare Dis 6: 70. doi:10.1186/1750-1172-6-70. PMC 3221642. PMID 22044607.
  6. ↑ E. C. Friedberg, G. C. Walker, W. Siede, R. D. Wood, R. A. Schultz and T. Ellenberger (2006). DNA repair and mutagenesis. Washington: ASM Press. p. 1118. ISBN 978-1-55581-319-2.
  7. 1 2 Brooks PJ DNA Repair (Amst). 2014 March 2; 7(7):1168-79.
  8. 1 2 Daya-Grosjean L, Sarasin A Mutat Res. 2014 March 2; 571(1-2):43-56
  9. ↑ Nussbaum, Robert; McInnes, Roderick; Willard, Huntington. Genetics in Medicine. Elsevier. ISBN 978-14377-0696-3.
  10. ↑ See the website of the movie, in German: http://www.mondscheinkinder-der-film.de/
  11. ↑ https://www.goodreads.com/book/show/18248415-the-deepest-secret?ac=1

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