Columbia Discovery Offers Hope for Rare Muscle Disease

Experimental treatment doubles or triples lifespan of mice with TK2 deficiency, leading to FDA approval for human use.

Published on Feb. 27, 2026

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When Arthur Estopiñan's 18-month-old son Arturito was diagnosed with a rare and usually fatal genetic disorder caused by a TK2 enzyme deficiency, most doctors said no treatment existed. But Columbia neurologist Michio Hirano had developed an experimental therapy using compounds that could potentially restore mitochondrial health and prevent muscle degeneration. After seeing promising results in mouse models, Hirano was able to get the treatment approved for compassionate use, and it has now dramatically improved the condition and lifespan of Arturito and over 100 other patients.

Why it matters

Mitochondrial diseases like TK2 deficiency are individually rare but collectively affect about 1 in 5,000 people. The success of the TK2 deficiency treatment developed by Dr. Hirano and his team demonstrates that it is possible to reverse some of the effects of mitochondrial dysfunction, offering hope for patients with other rare mitochondrial disorders.

The details

Hirano created a line of mice with TK2 deficiency and found that administering certain compounds could restore mitochondrial health and prevent muscle degeneration in the mice. When Arturito Estopiñan came to Hirano's clinic in a terminal stage of the disease, he was granted emergency compassionate use of the experimental therapy. Over time, Arturito regained motor functions and is now a thriving 15-year-old student. The therapy, now called KYGEVVI, was approved by the FDA in 2025 and is now helping over 100 other patients, dramatically improving their survival and motor functions.

  • In 2012, Hirano first spoke with Arthur Estopiñan about his son Arturito's diagnosis.
  • In the early 2010s, Hirano created the mouse model of TK2 deficiency that was essential for testing potential treatments.
  • In the mid-2010s, the first TK2 deficiency patients in Spain began receiving the experimental therapy developed by Hirano.
  • In 2019, Hirano opened a phase 2 clinical trial for the TK2 deficiency therapy.
  • In November 2025, the FDA approved the therapy, now called KYGEVVI, for TK2 deficiency patients whose symptoms emerge at or before age 12.

The players

Michio Hirano

A Columbia neurologist who developed an experimental therapy for the rare genetic disorder TK2 deficiency, which has dramatically improved outcomes for patients.

Arthur Estopiñan

The father of Arturito Estopiñan, who was diagnosed with TK2 deficiency as a toddler and received Hirano's experimental therapy, which saved his life.

Arturito Estopiñan

An 18-month-old boy diagnosed with the rare and usually fatal TK2 deficiency disorder, who received Hirano's experimental therapy and has since regained motor functions and is now a thriving 15-year-old student.

Olga Estopiñan

The mother of Arturito Estopiñan, who worked with her husband Arthur to support Hirano's research and help get the experimental therapy approved for compassionate use.

KYGEVVI

The name of the therapy developed by Hirano that was approved by the FDA in 2025 for treating TK2 deficiency in patients whose symptoms emerge at or before age 12.

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What they’re saying

“When Arturito came to us, he was in terrible condition, unfortunately, and in the terminal stage of the disease. He couldn't lift his arms or legs, he couldn't lift his head; he was like a rag doll.”

— Michio Hirano, Columbia neurologist (Mirage News)

“Obviously, without this treatment, my son would not be here today. Dr. Hirano and his team gave my son a second chance at life.”

— Arthur Estopiñan, Arturito's father (Muscular Dystrophy Association)

What’s next

Hirano continues to search for even better treatments and has found that a gene therapy combined with the drug therapy is markedly more effective in mice. He is also testing a different therapy for another rare mitochondrial deficiency disease.

The takeaway

The success of the TK2 deficiency therapy developed by Dr. Hirano and his team demonstrates that it is possible to reverse some of the effects of mitochondrial dysfunction, offering hope for patients with other rare and devastating genetic disorders. This breakthrough was made possible by the dedication of the research team, the support of patient families, and the collaborative efforts of doctors, scientists, funding agencies, and pharmaceutical companies.