von Hippel-Lindau disease

VHL disease follows Knudson's two-hit hypothesis: patients inherit one mutated VHL allele (tumor suppressor gene) and require a somatic mutation in the second allele for tumorigenesis. The VHL protein normally targets HIF-1α for ubiquitination and degradation under normoxic conditions. Loss of functional VHL protein leads to HIF-1α accumulation even in normoxia, causing pseudohypoxia and upregulation of VEGF, PDGF, and erythropoietin—explaining the highly vascular tumors and secondary polycythemia seen in this disease. Clinical manifestations include: (1) CNS hemangioblastomas (most commonly cerebellum, also spinal cord and retina) which can cause secondary erythrocytosis due to ectopic EPO production; (2) clear cell renal cell carcinoma (often bilateral and multiple, major cause of mortality); (3) pheochromocytomas (bilateral, often extra-adrenal); (4) pancreatic cysts and neuroendocrine tumors; (5) endolymphatic sac tumors; and (6) epididymal/broad ligament cystadenomas. Diagnosis is based on clinical criteria plus genetic testing for VHL mutations. Management involves surveillance with MRI brain/spine, abdominal imaging, and biochemical screening for pheochromocytoma, with surgical resection of tumors as needed. This is a classic board topic often tested by presenting a young patient with cerebellar mass (hemangioblastoma) plus polycythemia, or bilateral renal cell carcinomas at young age, or association with pheochromocytoma—triggering consideration of VHL syndrome and its relationship to HIF/VEGF pathway, which is also clinically relevant for understanding VEGF-targeted therapies (e.g., sunitinib, bevacizumab) in renal cell carcinoma.