A 5-year-old boy with severe short stature presents with a photosensitive telangiectatic erythema over the malar area and nose. He has had recurrent respiratory infections and has a family history of early-onset cancer. The defective protein is a:

• A DNA endonuclease
• B DNA helicase ✓
• C RNA splicing factor
• D Topoisomerase

Explanation

Bloom syndrome is an autosomal recessive disorder caused by mutations in the BLM gene, which encodes a RecQ DNA helicase. This leads to chromosomal instability and sister chromatid exchanges. The characteristic features include severe pre- and postnatal growth failure, photosensitive telangiectatic erythema in a malar distribution, immunodeficiency, and a marked predisposition to various malignancies. RECQL4 mutations cause Rothmund-Thomson syndrome, ERCC6 causes Cockayne syndrome, and TGM1 causes lamellar ichthyosis.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.