Walker Burger is beside himself with worry.
The 33-year-old relies on an experimental medicine to treat an ultra-rare disease called Barth syndrome that causes an enlarged heart, muscle weakness, and a shortened life expectancy. But the Food and Drug Administration last year refused to review the drug, despite prolonged efforts by its manufacturer, Stealth BioTherapeutics, to gather hard-to-come-by clinical data on such a tiny patient population.