Question

A rare autosomal recessive disease called xeroderma pigmentosum (XP) results in a number of phenotypic traits including abnormal skin pigmentation. People with this disease also exhibit a strong predisposition to skin cancer. This can be best explained by a:

A) Defect in DNA polymerase
B) Deficiency in base excision repair
C) Impairment in nucleotide excision repair
D) Mutation in the p53 gene

Answer 1

Xeroderma pigmentosum (XP) is characterized by an impaired nucleotide excision repair mechanism that fails to correct thymine dimers caused by UV exposure, leading to DNA distortion and an increased risk of skin cancer.

Step-by-step explanation:

The phenotypic traits and increased predisposition to skin cancer in patients with xeroderma pigmentosum (XP) can be best explained by an impairment in nucleotide excision repair. Patients with XP cannot effectively employ the nucleotide excision repair mechanism, which is critical for fixing DNA lesions caused by UV light. Exposure to UV light commonly leads to the formation of pyrimidine dimers, particularly thymine dimers, which distort the DNA's double helix structure. In individuals with XP, these dimers are not properly repaired due to a defective nucleotide excision repair system, which increases the risk of erroneous DNA replication and contributes to a higher likelihood of developing skin cancer.