Genetics testing startup 23andMe announced plan​s last​ week to start using its massive DNA database to develop new medical treatments, but some experts have questions about what that means for the more than 850,000 people who have submitted their data to the company.

The Google-backed company collects genetic info through $99 “spit kits” customers voluntarily send in for testing, touting an inte​rest in DNA collection for customer’s general “self-knowledge,” and to “empower individuals and develop new ways of accelerating research.” However, it faced ethical​ questions after partnering with major companies for drug development, and the scrutiny remains as it begins in-house, potentially lucrative drug development.

The move was seen by ​many as a “big​ shift” for the company, but Marcy Darnovsky, executive director Center for Genetics and Society, a nonprofit devoted to responsible uses of genetic technologies, suspects this was 23andMe’s plan from the outset.

“This wasn't a change in their business plan, it was the fulfillment of the next phase of the plan they’ve had since the beginning,” she told Motherboard. “To some people, it was clear...