QDPR (quinoid dihydropteridine reductase) is a critical enzyme that catalyzes the conversion of quinonoid dihydrobiopterin into tetrahydrobiopterin (BH4), an essential cofactor for neurotransmitter synthesis and amino acid metabolism 1. The enzyme functions in the cytoplasm, mitochondria, and cytosol, playing a vital role in maintaining the BH4/BH2 ratio through its NADH and NADPH binding activities 2. QDPR deficiency leads to dihydrobiopterin (BH2) accumulation and BH4 depletion, resulting in impaired neurotransmitter synthesis, oxidative stress, and increased reactive oxygen species generation 12. This enzyme deficiency is associated with hyperphenylalaninemia due to BH4 deficiency, causing neurological symptoms and developmental delays 34. In pancreatic cancer, QDPR deficiency promotes immune suppression by recruiting myeloid-derived suppressor cells through CXCL1/CXCR2 signaling, leading to resistance to immune checkpoint blockade therapy 2. Clinically, QDPR mutations cause dopa-responsive dystonia with tremor as a prominent feature 5, and early treatment of QDPR-deficient patients can result in near-normal mental development 3. The gene is located on chromosome 4.1-4p15.1 6, and comprehensive mutation analysis has identified multiple pathogenic variants in different populations 7.