Final answer:
People who are unable to repair thymine dimers caused by UV light suffer from xeroderma pigmentosum, resulting from a defect in nucleotide excision repair enzymes.
Step-by-step explanation:
Individuals who are genetically incapable of repairing pyrimidine dimers, specifically thymine dimers, formed due to ultraviolet light exposure are likely to suffer from xeroderma pigmentosum. This condition occurs because of a defect in the nucleotide excision repair mechanism that normally corrects such defects. As a result, thymine dimers remain uncorrected, distorting the structure of DNA and increasing the risk of skin lesions and skin cancer in affected individuals.