About a million tourists descend upon Roatán each year. The island, just off the coast of Honduras, boasts a large barrier reef ideal for scuba diving and snorkeling, and it has the beaches, jungles and slow pace of life prized by cruise ship types. One group of visitors, however, recently visited Roatán with a less conventional goal in mind: They’ve opted to become some of the first genetically enhanced humans.

These medical tourists came to receive a homegrown gene therapy made by Minicircle Inc., a small US startup. The therapy, delivered via injection, turbocharges the body’s production of follistatin, a protein that helps manage production of other proteins and hormones. The company’s founders say the therapy can reduce inflammation throughout the body, increase muscle mass and bone density, extend exercise endurance and improve hair and skin. It is, according to Minicircle, “the holy grail of muscle, bone and fat” and one of humanity’s best hopes for “extreme longevity.”