Xeroderma Pigmintosum (XP)

Medical Biochemistry and molecular Biology Department

Group Leader : 93-Esraa Samy Faried Abdelghafar.Members :91-Esraa Raafat Ahmed Ahmed. 92-Esraa Reda Hashem Tewfik.94-Esraa Saad Abaas Hamed.95-Esraa Shawkey Abdelhak Abolaban. 96-Esraa Sobhi Mohammed Abdelazez.97-Esraa Sabry Mohamed Ahmed Ali.98-Esraa Taher Elhosseiny Farag .

Researchers

Intended learninng outcomes (ILOS):1-Definition of XP disease.2- clinical introduction to the disease.3-illustration of biochemical and molecular mechanisms of disease.4-Symptoms of disease.5-Treatment of disease.6-summary.7-Refrences of information.

Disease definition• Xeroderma Pigmentosa (XP) is a genetic disorder

inherited as recessive autosomal trait that is caused by a defect in mechanisms that repair DNA mutations (as those caused by a ultraviolet light ) and is characterized by the development of pigment abnormalities and multiple skin cancers in areas exposed to the sun

Clinical introduction:

• XP is a disease happens because there is a defect in the DNA repair system. It is autosomally recessive inherited disease. Meaning that one must have2 reccesive XP genes to show signs of the disease. XP deos not allow the DNA repair system to mend the cell damage caused by UV rays,So the epidermis fall off with skin blisters.

Exposure of a cell to Ultraviolet light can result in covalent linking of adjacent pyrimidines (usually thymine) in the same DNA strand producing a dimar (pyrimidine»Thymine « dimar. ( The dimar prevent DNA polymerase action .)prevent DNA replication)

Biochemical and molecular mechanisms

• Repair of Thymine-Thymine dimers

• T^T dimers may be repaired by two mechanisms:

• (a) In photoreactivation repair, the PRE enzyme activated by blue light breaks the dimer, restoring the normal base pairing.

• (b) In excision repair,(The normal repair process)entails nucleotide excision. The damage is excised by endonucleases, then the gap is filled by a DNA polymerase and "sealed" by a ligase.

• Genatic defect in nucleotide excision repair system produce XP where thymine dimers are formed in the skin exposed to sun with producing of multiple skin cancer because some important genes has been badly affected , such as tumour suppressor genes and this disorder may lead to cancer.

symptoms:

• 1-Oozing,pussing,and blistering are seen on the epidermis. 2-The blisters eventually fall off along the epidermis .3-The epidermis is destroyed following an exposure to sun light,person is often prone to developing cancer.4-Spider like blood vessels under the skin.5-An eye exam show( keratisis,lid tumor and blepharitis).

Treatment of XP disease:• 1-patients need to use sun block with high SPF and must avoid all

contact with UV rays.2-Oral retinoids have been shown to decrease happening of skin cancer.3-Repairing DNA damage after UV exposure by delivery of DNA repair enzyme into the skin by means of SEL.4-Gene therapy for XP is still in an experimental stage by grafting skin that has the genitic defect.

Summary

1-WWW.emedicine.medscape.com.2-www.xps.org.

References of information: