Homocystinuria due to cystathionine beta-synthase (CBS) deficiency presents with Marfanoid habitus, ectopia lentis, thromboembolism, and intellectual disability. The lens dislocation in homocystinuria is characteristically in which direction, distinguishing it from Marfan syndrome?

• A Inferonasal (down and in), opposite to Marfan ✓
• B Superotemporal (up and out), same as Marfan
• C Posterior (towards vitreous)
• D Anterior (into anterior chamber)

Explanation

In homocystinuria, ectopia lentis occurs inferonasal (downward and inward) due to weakening of zonular fibers by homocysteine (which disrupts disulfide crosslinks). In Marfan syndrome, lens dislocation is characteristically superotemporal (upward and outward). This directional distinction is a classic NEET PG clinical discriminator. Homocystinuria is also distinguished by thromboembolism, mental retardation, and autosomal recessive inheritance.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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