Question

Child presents with sunlight causing eruptions, diagnosed with a DNA repair defect. Which defect could it be?

• A. Nucleotide excision
• B. Base excision repair
• C. Mismatch repair defect
• D. Recombination defect

Hint:

Nucleotide excision repair (NER) defects are associated with diseases such as xeroderma pigmentosum, where the body cannot repair UV-induced DNA damage.

Answer 1

The Correct Option is A

The child is experiencing skin eruptions when exposed to sunlight, a condition commonly associated with DNA repair defects. One notable disorder linked to this symptom is Xeroderma Pigmentosum (XP), which results from a defect in the Nucleotide Excision Repair (NER) pathway.

Here is why NER is the correct choice:

• Nucleotide Excision Repair: This pathway is responsible for repairing bulky DNA lesions, such as pyrimidine dimers, that result from ultraviolet (UV) radiation exposure. UV light from sunlight can damage the DNA by forming these dimers, which distort the DNA helix and require specialized repair mechanisms like NER.
• Base Excision Repair: This pathway fixes small, non-helix-distorting base lesions, such as those caused by oxidative damage, not necessarily related to sunlight exposure.
• Mismatch Repair defect: This system rectifies errors introduced during DNA replication, unrelated to direct sunlight damage.
• Recombination defect: Involves the repair of double-strand breaks and does not directly relate to UV-induced damage.

Given the symptoms and causal relationship between sunlight exposure and DNA repair mechanisms, a defect in Nucleotide Excision Repair is the most plausible cause for the condition exhibited by the child.