Which disorder is characterized by a purine metabolism defect leading to orange sand?

Lesch-Nyhan disorder is a genetic condition caused by a defect in purine metabolism, specifically due to the absence of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). This enzyme is critical for the recycling of purines, which are essential building blocks of DNA and RNA. The lack of HGPRT leads to an accumulation of uric acid in the body. As uric acid concentrations increase, it can crystallize and be excreted in the urine, manifesting as orange sand, which is essentially crystallized uric acid deposits that can be seen on the diaper of infants or in urine samples.

This condition not only leads to physical symptoms but also neurological issues, such as self-injurious behavior. The association of orange sand in the urine with Lesch-Nyhan disorder is a distinguishing feature that helps in its identification, providing insight into the metabolic disruption occurring in the body.

The other options—hemophilia, alkaptonuria, and phenylketonuria—are associated with different metabolic defects and clinical presentations, which do not involve the characteristic orange sand in urine due to purine metabolism disruptions.