Bit · Genetics
NF1 vs NF2 vs Tuberous Sclerosis vs VHL
Four autosomal dominant neurocutaneous (phakomatosis) syndromes. Each has a different tumor-suppressor gene and a different signature tumor / skin lesion.
Mechanism
Each is autosomal dominant with high penetrance, caused by loss of a different tumor suppressor:
- Neurofibromatosis Type 1 (NF1) — chromosome 17, NF1 gene → encodes neurofibromin (negative regulator of Ras). Findings (NIH criteria — need 2+): café-au-lait macules (≥6, >5 mm prepubertal or >15 mm post), cutaneous neurofibromas, axillary/inguinal freckling, Lisch nodules (iris hamartomas), optic glioma, sphenoid wing dysplasia, first-degree relative. Increased risk of pheochromocytoma.
- Neurofibromatosis Type 2 (NF2) — chromosome 22, NF2 gene → encodes merlin. Signature lesion: bilateral vestibular schwannomas (CN VIII, often presenting in teens/young adults with hearing loss). Also juvenile cataracts, meningiomas, ependymomas. Skin findings minimal compared to NF1.
- Tuberous Sclerosis Complex (TSC) — TSC1 (hamartin, chr 9) or TSC2 (tuberin, chr 16) → mTOR pathway overactivation. Signature lesions: ash-leaf spots (hypopigmented macules, best seen under Wood lamp), shagreen patches, angiofibromas ('adenoma sebaceum') on the face, subependymal giant cell astrocytomas, cortical tubers (cause seizures + intellectual disability), cardiac rhabdomyomas (often regress), renal angiomyolipomas.
- von Hippel-Lindau (VHL) — chromosome 3p, VHL gene → HIF-α regulation. Findings: hemangioblastomas (cerebellum, spine, retina), clear cell renal cell carcinoma (multiple, bilateral), pheochromocytoma, pancreatic neuroendocrine tumors, endolymphatic sac tumors.
Differentiator Table
| NF1 | NF2 | Tuberous Sclerosis | VHL | |
| Gene / chromosome | NF1 (neurofibromin) / 17 | NF2 (merlin) / 22 | TSC1 (hamartin, 9) / TSC2 (tuberin, 16) | VHL / 3p |
| Inheritance | Autosomal dominant | Autosomal dominant | Autosomal dominant | Autosomal dominant |
| Skin findings | Café-au-lait, freckling, neurofibromas | Few skin findings | Ash-leaf spots, shagreen patches, angiofibromas | Few skin findings |
| Eye findings | Lisch nodules, optic glioma | Juvenile cataracts | Retinal hamartomas | Retinal hemangioblastoma |
| Signature tumor | Neurofibroma, optic glioma, MPNST | Bilateral vestibular schwannomas | Cortical tubers, SEGA, cardiac rhabdomyoma, renal angiomyolipoma | Cerebellar/retinal hemangioblastoma, clear-cell RCC, pheochromocytoma |
| Seizures / intellectual disability | Variable | Uncommon | COMMON (cortical tubers) | Uncommon |
| Mnemonic for the chromosome | '17' — NF1 (count letters) | '22' — NF2 doubled | 9 and 16 | VHL: chromosome 3p ('Von HippeL = 3 letters') |
The Pivot
Three questions:
- Café-au-lait macules + neurofibromas + Lisch nodules? → NF1.
- Bilateral hearing loss + vestibular schwannomas? → NF2.
- Ash-leaf spots + seizures + cardiac rhabdomyoma? → TSC.
- Cerebellar hemangioblastoma + clear-cell RCC + pheochromocytoma? → VHL.
Pheochromocytoma overlap: VHL, NF1, and MEN 2A/2B all increase pheo risk — check for the syndromic features.
NBME-Style Stem
A 4-year-old girl with epilepsy is found to have multiple hypopigmented macules on her trunk (visible under Wood lamp), a thickened plaque on her lower back, and small papules on her cheeks. Brain MRI shows multiple cortical tubers and a subependymal giant cell astrocytoma. Echocardiogram reveals a cardiac mass. Which of the following is the most likely diagnosis?
Concept Anchor
Four neurocutaneous syndromes, four tumor suppressors, four signature tumors: neurofibromin (NF1), merlin (NF2), hamartin/tuberin (TSC), VHL. The skin lesion and the signature tumor tell you which one before any genetic test.