Defective DNA repair is associated with(LQ)
2). This extensively studied process consists of the removal and the replacement of damaged DNA with new DNA.
3). Two types of NER exist: global genome (GG-NER) and transcription coupled (TC-NER).
4). The last decade has seen the cloning of the key elements of NER, and the process has been reconstituted in vitro.
5). In addition to the defects in the repair genes, UV-B radiation also has immunosuppressive effects that may be involved in the pathogenesis of xeroderma pigmentosum. Although typical symptoms of immune deficiency, such as multiple infections, are not usually observed in patients with xeroderma pigmentosum, several immunologic abnormalities have been described in the skin of patients with xeroderma pigmentosum.
6). Clinical studies of the skin of patients with xeroderma pigmentosum indicate prominent depletion of Langerhans cells induced by UV radiation.
7). Various other defects in cell-mediated immunity have been reported in xeroderma pigmentosum.
8). These defects include impaired cutaneous responses to recall antigens, decreased ratio of circulating T-helper cells to suppressor cells, impaired lymphocyte proliferative responses to mitogen, impaired production of interferon in lymphocytes, and reduced natural killer cell activity.
9). At birth the skin is normal. First thing to appear is freckles on sun exposed area. By the age of 20, various benign and malignant tumors develop. Associated features are ocular lesions like photophobia, cojuctivitis and various neurological complications.