**Core Concept**
Xeroderma Pigmentosum (XP) is a rare genetic disorder characterized by an impaired ability to repair DNA damage caused by ultraviolet (UV) radiation from the sun or other sources. This impairment leads to an increased risk of skin cancer and other skin-related complications.

**Why the Correct Answer is Right**
XP is primarily caused by mutations in genes involved in the nucleotide excision repair (NER) pathway, which is responsible for repairing UV-induced DNA damage. The correct inheritance pattern for XP is autosomal recessive, not autosomal dominant. This means that an individual must inherit two mutated copies of the gene (one from each parent) to express the condition. The defective DNA repair mechanism in XP leads to the accumulation of mutations, particularly in genes involved in cell cycle regulation, resulting in an increased risk of skin cancer, including squamous cell carcinoma.

**Why Each Wrong Option is Incorrect**
**Option A:** XP is not inherited in an autosomal dominant manner. Autosomal dominant inheritance would require only one mutated copy of the gene to express the condition.
**Option B:** This statement is true. XP is indeed caused by defective DNA repair mechanisms, specifically the NER pathway.
**Option C:** This statement is true. XP is associated with an increased risk of skin cancers, including squamous cell carcinoma, due to the impaired DNA repair mechanism.
**Option D:** This statement is related to the pathophysiology of XP. Thymine dimers are a type of DNA damage caused by UV radiation, which is repaired by the NER pathway in individuals with normal DNA repair function.

**Clinical Pearl / High-Yield Fact**
XP patients are highly susceptible to skin cancer due to their impaired ability to repair UV-induced DNA damage. A key clinical correlation is that XP patients often develop skin cancers at a younger age than the general population, highlighting the importance of sun protection measures in this patient group.

**✓ Correct Answer: A. It is autosomal dominant inheritance**