GCH1 and cancer: Specifically, GCH1 mutations can lead to tetrahydrobiopterin deficiency, resulting in phenylketonuria (37, 48, 51); elevated NAMPT expression may enhance cancer cell growth and survival, contributing to tumor development (52, 53); UGDH dysfunction can disrupt extracellular matrix composition, affecting tissue structure and function, with links to cancer and fibrosis (54); and increased P4HA expression may facilitate tumor progression and metastasis (55).