Source / episode info

• **Episode:**662
• **Title:**DIP Ep 662: The Genetics Sprint (for Step 2 and 3) Part 2
• **Published:**2026-07-10
• Source:Episode page

One-liner

This episode is a high-yield review of autosomal dominant cancer predisposition syndromes, emphasizing the mechanism (TSG mutation/loss of heterozygosity) and classic clinical findings for NF1, NF2, VHL, TSC, Li-Fraumeni Syndrome, BRCA, and FAP.

High-yield summary

• NF1: Autosomal dominant; neurofibromin gene on Chromosome 17. Key features include café-au-lait spots, neurofibromas, Lisch nodules (iris hamartomas), and increased risk of pheochromocytoma.
• NF2: Autosomal dominant; Merlin gene mutation on Chromosome 22. Characterized by the triad of bilateral vestibular schwannomas, meningiomas, and epidermoid/appendixomas (MSME).
• VHL Disease: Autosomal dominant; VHL gene on Chromosome 3. Loss of function prevents HIF- degradation, leading to excessive angiogenic factors and hemangioblastomas (especially in the posterior fossa) and bilateral clear-cell retinal carcinomas.
• TSC Complex: Autosomal dominant; mutations in TSC1 or TSC2. Inhibits mTOR signaling. Key findings include ash leaf spots, facial angiofibromas, cardiac rhabdomyomas, and renal angiomyolipomas.
• LFS Syndrome: Autosomal dominant; mutation in the p53 gene. Associated with a "LABS" mnemonic: Leukemia, Adrenal cortical cancers, Breast cancer, Sarcomas.
• FAP: Autosomal dominant; mutation in the APC gene (Chromosome 5). Leads to constitutive WNT signaling and thousands of colonic polyps, making colon cancer nearly inevitable without prophylactic colectomy.

Learning objectives

• Differentiate the clinical manifestations and genetic basis of NF1 vs. NF2.
• Identify the key features (e.g., posterior fossa hemangioblastomas) associated with VHL disease.
• Correlate specific skin findings (ash leaf spots, café-au-lait spots) with their respective syndromes (TSC, NF1).
• Understand the mechanism of action and clinical implications of APC mutations in FAP.
• Apply knowledge of tumor suppressor gene function (e.g., p53, APC, neurofibromin) to predict associated cancers.