Lucas and Luna explore how AI diagnostic tools systematically underdiagnose patients with rare diseases—those affecting fewer than 200,000 people. They break down the data imbalance problem: rare diseases collectively affect 300 million people worldwide, but AI training datasets overwhelmingly favor common conditions. The hosts examine a 2025 study from the Journal of the American Medical Informatics Association showing that diagnostic AI models misdiagnose rare diseases at rates 30% higher than common ones, with false-negative rates reaching 60% for conditions with fewer than 1,000 documented cases. They discuss real-world consequences: delayed treatment, misdirected care, and the psychological toll of being told 'it's all in your head.' Lucas and Luna also consider potential solutions—federated learning across rare-disease registries, synthetic data augmentation, and regulatory nudges from the FDA's new AI validation guidelines proposed in March 2026. This episode asks a pointed question: how do we build AI that doesn't fail the very patients who need it most?