Which genetic defect is associated with Lesch-Nyhan syndrome?

Lesch-Nyhan syndrome is directly caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). This enzyme is crucial in the purine salvage pathway, which recycles purines to form nucleotides. When HGPRT is deficient, there is an accumulation of uric acid due to the increased degradation of purines, leading to hyperuricemia. This metabolic disturbance is associated with the hallmark features of Lesch-Nyhan syndrome, which include self-mutilating behaviors, neurological manifestations, and gout-like symptoms.

The other choices do not relate to Lesch-Nyhan syndrome. The XIST gene relates to X chromosome inactivation, and its mutations are associated with disorders related to X-linked conditions and not specifically Lesch-Nyhan syndrome. Phenylalanine hydroxylase deficiency is the cause of phenylketonuria, an entirely different metabolic disorder characterized by the inability to metabolize phenylalanine. The beta-globin gene mutation is associated with various forms of anemia, including sickle cell disease and beta-thalassemia, which again are unrelated to Lesch-Nyhan syndrome. Hence, HGPRTase deficiency is the correct