Twins Samantha Schilit (left) and Arielle Schilit Nitenson (right) at Nitenson’s wedding in 2013.

In August 2015, Samantha Schilit went to her primary care doctor to get a blood draw. A PhD candidate at Harvard specializing in human genetics, she was itching to unlock the secrets of her genes with a test called whole-genome sequencing, which provides a full readout of a person’s DNA.

Patients must give their informed consent before undergoing whole-genome sequencing or any other genetic test. But there are no laws that restrict what patients can do with their own genetic information, or that require patients’ family members to be involved in the consent process. This raises questions about who owns an individual’s genetic code, since family members share many genetic traits and may harbor the same genetic abnormalities associated with certain diseases.

When Schilit got her test results back a few months later, she didn’t consider that her identical twin sister Arielle Schilit Nitenson, a PhD student in neuroscience at Brown University, would have concerns about the test. The two co-authored an article in the Journal of Genetic Counseling about their experience.

“Your genes don’t really belong to you,” Nitenson says. As identical twins, Schilit and Nitenson share nearly the same genome. So any important information Schilit learned from the test would also be relevant to Nitenson.

But unlike her sister, Nitenson wasn’t as eager to learn what possible mutations might be lurking in her DNA, and she was worried about who would have access to the data. She didn’t want her information to be used for research purposes or by an insurance company to discriminate against her. Congress passed the Genetic Information Nondiscrimination Act in 2008, but while it prevents genetic discrimination for employment and health insurance, it doesn’t cover life, disability, or long-term care insurance.

David Flannery, medical director at the American College of Medical Genetics and Genomics, an organization made up of genetics professionals, says concerns about privacy and sharing of genetic data aren’t new. But these issues have become more complex since whole-genome tests became commercially available in 2013. These tests produce huge amounts of data, only a tiny fraction of which scientists are able to link to disease risk.

As it turned out, the results of Schilit’s test showed that the twins had a pretty healthy genome. They found out they were genetic carriers for only a handful of mild medical conditions, but one of them became dangerous when Nitenson became pregnant with her first child earlier this year. One of her genetic mutations could cause problems during labor. The genetic abnormality means that certain common pain alleviation methods and delivery techniques pose a risk for Nitenson and her baby. Armed with that knowledge, Nitenson, now 28 weeks pregnant, told her obstetrician so they could make an alternative plan for her delivery.

Nitenson didn’t want to disclose the genetic abnormality over concerns for her unborn daughter’s privacy, even though her sister was willing to divulge that information publicly. But Schilit and Nitenson came to an agreement about what they are both comfortable sharing and what should be kept private.

Laura Hercher, a professor at Sarah Lawrence College who teaches ethical issues in genetic counseling, says the way the twins handled their genetic information is the best-case scenario for a family in which a member undergoes genetic testing.

The consent process for whole-genome and whole-exome sequencing is “all over the map,” she says. Some companies that manufacture these tests have their own consent forms, while clinics and health-care systems that offer genome sequencing have their own procedures for communicating to patients the possible benefits and consequences of genetic testing. Most tests require a physician’s signature for authorization, regardless of whether the doctor has any special training in genetics.

Schilit says she mentioned her twin to the physician who ordered the test, but she says “there was never a conversation about my twin and the implications” of the test results for her.

Hercher says doctors are responsible for telling patients to notify family members if genetic mutations related to certain serious diseases are discovered in a genomic sequencing test. But ultimately, “family members don’t have veto powers” over a relative’s decision to get genetic testing, she says.