A 6-year-old boy with short stature, microcephaly, and bilateral absent thumbs develops progressive pancytopenia with macrocytic anemia. Bone marrow shows hypoplasia. Skin examination notes diffuse hyperpigmentation and several cafe-au-lait macules. Which confirmatory test should be ordered?

• A Plasma 7-dehydrocholesterol level
• B Serum alpha-fetoprotein level
• C Karyotype after diepoxybutane exposure of lymphocytes ✓
• D Urinary glycosaminoglycan quantification

Explanation

Fanconi anemia presents with radial ray defects such as absent or hypoplastic thumbs, short stature, skin hyperpigmentation, and bone marrow failure typically around 5 to 7 years of age. Diagnosis rests on demonstrating increased chromosomal fragility: culturing lymphocytes with diepoxybutane or mitomycin A reveals characteristic breaks and radial figures. Elevated alpha-fetoprotein suggests ataxia telangiectasia, 7-dehydrocholesterol indicates Smith-Lemli-Opitz syndrome, and glycosaminoglycans indicate mucopolysaccharidosis.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.