A 6-year-old boy is brought to the office due to a persistent facial ulcer for the past 2 months. His mother reports that the patient has extreme sensitivity to sunlight and has developed freckles on his face, neck, and limbs since infancy. On physical examination, the skin in sun-exposed areas is dry and rough with numerous freckles and erythematous macules. There is an ulcerated plaque on the left face; a biopsy reveals squamous cell carcinoma. Further testing leads to a diagnosis of xeroderma pigmentosum. A defect in which of the following enzymes is most likely causing this patient's condition?

Question

A 6-year-old boy is brought to the office due to a persistent facial ulcer for the past 2 months.  His mother reports that the patient has extreme sensitivity to sunlight and has developed freckles on his face, neck, and limbs since infancy.  On physical examination, the skin in sun-exposed areas is dry and rough with numerous freckles and erythematous macules.  There is an ulcerated plaque on the left face; a biopsy reveals squamous cell carcinoma.  Further testing leads to a diagnosis of xeroderma pigmentosum.  A defect in which of the following enzymes is most likely causing this patient's condition?

Quizplus · Accepted Answer

Eductional Objective: Xeroderma pigmentosum is an autosomal recessive disorder characterized by defective nucleotide excision repair often caused by a deficiency in UV-specific endonuclease.  Affected children usually have severe photosensitivity, hyperpigmentation in sun-exposed areas, and a greatly increased risk for skin cancer.

A 6-Year-Old Boy Is Brought to the Office Due to a Persistent