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A Genetic Appeal?

Newsweek describes the case of a convicted man attempting to use the so-called "warrior gene" as the basis of an appeal in the 2012 murder of his girlfriend's step-grandfather.

Anthony Blas Yepez and his lawyer are arguing before the New Mexico Supreme Court this week, K. Thor Jensen notes. They suggest Yepez should receive a new trial for strangling and setting the elderly man on fire, based on positive results from a "$99 procedure to test Yepez for a genetic mutation that has been scientifically linked to increased aggression."

The monoamine oxidase A (MAOA) enzyme-coding gene has been implicated in aggressive behavior for decades. For example, a variant associated with lower-than-usual MAOA levels appeared to be overrepresented in repeat violent offenders in a 2014 study. Even so, its causal role in aggression has been disputed and mutations in the gene are relatively common.

That has New Mexico prosecutors calling the MAOA defense "a novel and unsubstantiated theory," according to an Associated Press piece by Morgan Lee that was picked up by The Washington Post.

In 2015, Yepez was convicted of a handful of crimes, including second-degree murder and evidence tampering. In the past, prosecutors in the case successfully argued that science related to MAOA "was not settled … preventing Yepez's lawyer from pursuing the strategy in court."

"If Yepez's appeal is successful, it will set a new precedent in the United States on the acceptability of the 'warrior gene' defense in violent crimes," Jensen notes in Newsweek.

The appeal could see the case sent back to New Mexico's First Judicial District Court, reporter Robert Nott explains in the Santa Fe New Mexican, where the genetic evidence could potentially impact the sentence Yepez receives for the crime and "provide an example to courts around the nation" around the application of behavioral genetics theories.

In 2014, the New York State Psychiatric Institute's Paul Appelbaum and others raised concerns around the use — and potential misinterpretation — of genetics in criminal and civil court cases.