Question

A 5-year-old girl is brought to the physician by her mother. The mother tells you that the girl's skin becomes red and scaling with only minimal sun exposure. She began to notice this phenomenon when the child was 7 months old. Now the girl's skin is thin and hyperpigmented. The patient has a few nevi on her hands that have been rapidly enlarging. The defective gene in this patient is responsible for

Option 1: Regulation of cell cycle
Option 2: Signal transduction
Option 3: DNA excision repair
Option 4: DNA mismatch repair

Answer 1

The patient's symptoms suggest she has xeroderma pigmentosum, which is caused by a defective gene responsible for DNA excision repair, leading to a high risk of skin cancer.

Step-by-step explanation:

The defective gene in the patient described, who exhibits symptoms of red, scaling skin with minimal sun exposure and rapidly enlarging nevi, is responsible for DNA excision repair, specifically nucleotide excision repair (NER). This is indicative of the condition known as xeroderma pigmentosum, where patients are unable to repair damage caused by UV light, such as the formation of thymine dimers. These dimers significantly distort the DNA structure, leading to an increased risk of skin cancer.