You are examining a 7-year-old girl brought to you by her parents because they are concerned about the severe skin blistering on her arms and back of her neck a few days after she played in the sun for 15 minutes without sunscreen. Physical examination shows the girl has numerous freckles on her face, neck, arms, and hands. In addition she has numerous telangiectasias on her arms as well as crusty and scaly patches of skin. You suspect the child may have xeroderma pigmentosum. Which of the following processes is most likely to be defective in this child if your diagnosis is correct?

Question

Quizplus · Accepted Answer

Xeroderma pigmentosum is caused by a defect in nucleotide excision repair, which is responsible for removing thymine dimers caused by UV light. Xeroderma pigmentosum is characterized clinically by sun sensitivity that results in progressive degeneration of sun-exposed areas of the skin and eyes. Often these changes will result in neoplasia. There are currently 8 alleles whose mutations result in manifestation of XP. Seven of the genes are involved in processes of nucleotide excision repair (NER) including pyrimidine dimer removal. In most XP patients the initial symptoms are an abnormal reaction to sun exposure which includes severe sunburn with blistering and persistent erythema with minimal exposure to the sun. These symptoms most often manifest between 1 and 2 years, although some patients do not exhibit symptoms until the teens. Most XP patients will develop xerosis (dry skin) and poikiloderma (referring to areas of increased pigment alternating with areas of reduced pigment, atrophy, and telangiectasias). Telangiectasias are areas of the skin under which there are dilated superficial vessels.

You Are Examining a 7-Year-Old Girl Brought to You by Her