8-year-old with rare, fatal disease shows dramatic improvement on experimental treatment

Medical illustration of a mitochondrion against a black background. The outline of the mitochondrion is in fluorescent purple and is undulating. Inside, there are fluorescent orange and yellow blobs and circles, as well as patches of fluorescent green and blue. .

The 8-year-old boy declined rapidly over only a few months. In August 2023, he was running and playing soccer, but by September, involuntary muscle contractions took hold of both his ankles. By October, he'd lost the ability to run and play sports, and by late November, he fell down frequently enough that physical therapists advised his family to get him a wheelchair.

Genetic testing confirmed the cause of the child's sudden deterioration: He carried two mutant copies of a gene called HPDL. The HPDL protein helps make an antioxidant, called coenzyme Q10, that is critical to the functioning of mitochondria, the powerhouses of cells.