A Milestone Years in the Making: Dr. Michio Hirano’s Breakthrough in Treating TK2 Deficiency

More than a decade ago, Dr. Michio Hirano began investigating an ultra-rare and fatal mitochondrial disease known as Thymidine Kinase 2 deficiency (TK2d). One of his earliest patients was Arturo Estopiñán Jr. (pictured right with his family), who was diagnosed at just about a year old and not expected to survive to his third birthday. 

In 2012, Dr. Hirano was developing a mouse model to better understand TK2d and lay the groundwork for potential treatment. Two years later, his team had published the first evidence of in vivo efficacy and safety for deoxynucleoside therapy, opening the door for compassionate-use treatment in Arturo and a small number of children worldwide. By 2018, Arturo was attending school, learning to read and write, and steadily gaining strength—an outcome once unimaginable.

Last week, following newly published study results by Dr. Hirano and colleagues, the FDA approved KYGEVVI®, the first therapy for TK2 deficiency. In the announcement, Arturo’s mother, Olga, said: “Dr. Hirano and his team gave my son a second chance at life.” 

We extend our deepest congratulations to Dr. Hirano and team, whose unwavering commitment to TK2d research has changed the course of a once-untreatable disease and transformed what is possible for patients everywhere. We are equally grateful to the Estopiñán family and to the many TK2d families whose trust, advocacy, and fundraising helped sustain this effort, and to the Muscular Dystrophy Association (MDA) and National Institutes of Health (NIH) for their steadfast support of both the science and the families behind it.

The MDA has released a short video telling Arturo’s very moving story, featuring Dr. Hirano’s reflections on the path from compassionate use to FDA approval. To learn more or explore ways to support this work, please contact Matthew Reals.