Final answer:
Xeroderma pigmentosum is caused by a deficiency in the DNA repair system, leading to an inability to repair thymine dimers formed by UV exposure and increasing the risk of skin cancer.
Step-by-step explanation:
Xeroderma pigmentosum (XP) is a genetic disorder caused by a deficiency in the body's ability to repair damage to DNA resulting from exposure to ultraviolet (UV) light. This condition stems from mutations in genes responsible for nucleotide excision repair, a crucial mechanism that fixes DNA damage caused by UV radiation. Individuals with XP are highly sensitive to sunlight, and their skin lacks the ability to repair the DNA damage caused by UV rays. Consequently, this heightened sensitivity leads to an increased risk of developing skin cancers, such as basal cell carcinoma, squamous cell carcinoma, and melanoma, at a young age. Moreover, XP patients may also experience skin changes, pigmentary abnormalities, and premature aging of the skin due to the inability to repair DNA damage caused by UV exposure. Protective measures such as avoiding sunlight and using protective clothing are essential for managing XP to reduce the risk of skin damage and cancer development. The correct answer is c. XP patients possess a deficient DNA repair system.