Imagine this scenario: A couple is involved in a heated custody dispute over their only child. As part of the effort to make the case of being a better guardian, one parent goes on a "genetic fishing expedition": this parent obtains a DNA sample from the other parent with the hope that such data will identify some genetic predisposition to a psychiatric condition (e.g., schizophrenia) and tilt the judge's custody decision in his or her favor.

As knowledge of psychiatric genetics is growing, it is likely to be introduced in civil cases, such as child custody disputes and education-related cases, raising a tangle of ethical and legal questions.

This is an example of how "behavioral genetic evidence" -- an umbrella term for information gathered from family history and genetic testing about pathological behaviors, including psychiatric conditions—may in the future be brought by litigants in court proceedings. Such evidence has been discussed primarily when criminal defendants sought to introduce it to make the claim that they are not responsible for their behavior or to justify their request for reduced sentencing and more lenient punishment.

However, civil cases are an emerging frontier for behavioral genetic evidence. It has already been introduced in tort litigation, such as personal injury claims, and as knowledge of psychiatric genetics is growing, it is further likely to be introduced in other civil cases, such as child custody disputes and education-related cases. But the introduction of such evidence raises a tangle of ethical and legal questions that civil courts will need to address. For example: how should such data be obtained? Who should get to present it and under what circumstances? And does the use of such evidence fit with the purposes of administering justice?

How Did We Get Here?

That behavioral genetic evidence is entering courts is unsurprising. Scientific evidence is a common feature of judicial proceedings, and genetic information may reveal relevant findings. For example, genetic evidence may elucidate whether a child's medical condition is due to genetic causes or medical malpractice, and it has been routinely used to identify alleged offenders or putative fathers. But behavioral genetic evidence is different from such other genetic data – it is shades of gray, instead of black and white.

Although efforts to understand the nature and origins of human behavior are ongoing, existing and likely future knowledge about behavioral genetics is limited. Behavioral disorders are highly complex and diverse. They commonly involve not one but multiple genes, each with a relatively small effect. They are impacted by many, yet unknown, interactions between genes, familial, and environmental factors such as poverty and childhood adversity.

And a specific gene variant may be associated with more than one behavioral disorder and be manifested with significantly different symptoms. Thus, biomarkers about "predispositions" for behavioral disorders cannot generally provide a diagnosis or an accurate estimate of whether, when, and at what severity a behavioral disorder will occur. And, unlike genetic testing that can confirm litigants' identity with 99.99% probability, behavioral genetic evidence is far more speculative.

Genetic theft raises questions about whose behavioral data are being obtained, by whom, and with what authority.

Whether judges, jurors, and other experts understand the nuances of behavioral genetics is unclear. Many people over-estimate the deterministic nature of genetics, and under-estimate the role of environments, especially with regards to mental health status. The U.S. individualistic culture of self-reliance and independence may further tilt the judicial scales because litigants in civil courts may be unjustly blamed for their "bad genes" while structural and societal determinants that lead to poor behavioral outcomes are ignored.

These concerns were recently captured in the Netflix series "13 Reasons Why," depicting a negligence lawsuit against a school brought by parents of a high-school student there (Hannah) who committed suicide. The legal tides shifted from the school's negligence in tolerating a culture of bullying to parental responsibility once cross-examination of Hannah's mother revealed a family history of anxiety, and the possibility that Hannah had a predisposition for mental illness, which (arguably) required therapy even in the absence of clear symptoms.

Where Is This Going?

The concerns are exacerbated given the ways in which behavioral genetic evidence may come to court in the future. One way is through "genetic theft," where genetic evidence is obtained from deserted property, such as soft-drink cans. This method is often used for identification purposes such as criminal and paternity proceedings, and it will likely expand to behavioral genetic data once available through "home kits" that are offered by direct-to-consumer companies.

Genetic theft raises questions about whose behavioral data are being obtained, by whom, and with what authority. In the scenario of child-custody dispute, for example, the sequencing of the other parent's DNA will necessarily intrude on the privacy of that parent, even as the scientific value of such information is limited. A parent on a "genetic fishing expedition" can also secretly sequence their child for psychiatric genetic predispositions, arguably, in order to take preventative measures to reduce the child's risk for developing a behavioral disorder. But should a parent be allowed to sequence the child without the other parent's consent, or regardless of whether the results will provide medical benefits to the child?

Similarly, although schools are required, and may be held accountable for failing to identify children with behavioral disabilities and to evaluate their educational needs, some parents may decline their child's evaluation by mental health professionals. Should schools secretly obtain a sample and sequence children for behavioral disorders, regardless of parental consent? My study of parents found that the overwhelming majority opposed imposed genetic testing by school authorities. But should parental preference or the child's best interests be the determinative factor? Alternatively, could schools use secretly obtained genetic data as a defense that they are fulfilling the child-find requirement under the law?

The stigma associated with behavioral disorders may intimidate some people enough that they back down from just claims.

In general, samples obtained through genetic theft may not meet the legal requirements for admissible evidence, and as these examples suggest, they also involve privacy infringement that may be unjustified in civil litigation. But their introduction in courts may influence judicial proceedings. It is hard to disregard such evidence even if decision-makers are told to ignore it.

The costs associated with genetic testing may further intensify power differences among litigants. Because not everyone can pay for DNA sequencing, there is a risk that those with more resources will be "better off" in court proceedings. Simultaneously, the stigma associated with behavioral disorders may intimidate some people enough that they back down from just claims. For example, a good parent may give up a custody claim to avoid disclosure of his or her genetic predispositions for psychiatric conditions. Regulating this area of law is necessary to prevent misuses of scientific technologies and to ensure that powerful actors do not have an unfair advantage over weaker litigants.

Behavioral genetic evidence may also enter the courts through subpoena of data obtained in clinical, research or other commercial genomic settings such as ancestry testing (similar to the genealogy database recently used to identify the Golden State Killer). Although court orders to testify or present evidence are common, their use for obtaining behavioral genetic evidence raises concerns.

One worry is that it may be over-intrusive. Because behavioral genetics are heritable, such data may reveal information not only about the individual litigant but also about other family members who may subsequently be stigmatized as well. And, even if we assume that many people may be willing for their data in genomic databases to be used to identify relatives who committed crimes (e.g., a rapist or a murderer), we can't assume the same for civil litigation, where the public interest in disclosure is far weaker.

Another worry is that it may deter people from participating in activities that society has an interest in advancing, including medical treatment involving genetic testing and genomic research. To address this concern, existing policy provides expanded privacy protections for NIH-funded genomic research by automatically issuing a Certificate of Confidentiality that prohibits disclosure of identifiable information in any Federal, State, or local civil, criminal, and other legal proceedings.

But this policy has limitations. It applies only to specific research settings and does not cover non-NIH funded research or clinical testing. The Certificate's protections can also be waived under certain circumstances. People who volunteer to participate in non-NIH-funded genomic research for the public good may thus find themselves worse-off if embroiled in legal proceedings.

Consider the following: if a parent in a child custody dispute had participated in a genetic study on schizophrenia years earlier, should the genetic results be subpoenaed by the court – and weaponized by the other parent? Public policy should aim to reduce the risks for such individuals. The end of obtaining behavioral genetic evidence cannot, and should not, always justify the means.