SCID

Enzymatic defects in purine and pyrimidine metabolism can present with diverse clinical features, including failure to thrive, megaloblastic anemia, hyperuricemia, or hyperammonemia. Key disorders include UMP synthase deficiency (orotic aciduria), OTC deficiency, ADA deficiency leading to SCID, and Lesch-Nyhan syndrome. Regulation through feedback inhibition and enzyme targets like ribonucleotide reductase are essential concepts for understanding metabolism and clinical interventions.