Final answer:
Xeroderma pigmentosa is a primary keratinization defect that affects the skin's ability to repair damage caused by UV light. It is characterized by a defect in the nucleotide excision repair enzymes, resulting in the distortion of the DNA double helix. This condition increases the risk of skin cancer.
Step-by-step explanation:
Xeroderma pigmentosa is a well-studied example of a primary keratinization defect. It is a rare genetic disorder that affects the skin's ability to repair damage caused by ultraviolet (UV) light. People with xeroderma pigmentosa have a defect in the nucleotide excision repair enzymes, which prevents them from repairing thymine dimers, causing the structure of the DNA double helix to be distorted. This condition leads to a high risk of skin cancer.