Familial DNA searches may misidentify family members

Familial searching is a relatively new forensic technique to identify a perpetrator if a crime scene DNA sample has no matches in a DNA database. In such a situation, law enforcement can look for a partial match to a known person in the database - a ‘near miss’ - in the hope that the closeness of the genetic profiles indicates that one of that person’s relatives is the perpetrator.

But research published in the journal PLOS ONE, conducted by Rori Rohlfs and colleagues from the University of California at Berkeley and New York University, indicates that familial search methods may identify distant relatives as being closer to the perpetrator than they actually are.

The researchers adopted the criteria used by the state of California and carried out the method on a simulation study of randomly generated profiles of related and unrelated individuals. They found that while there is a low probability of unrelated individuals being identified as a first-degree relative (ie, parent, sibling or offspring), there is a 3-18% chance that a first cousin of a known offender could be misidentified as a full sibling (depending on the population background) and up to a 42% chance that a half sibling could be misidentified as a full sibling.

The prevalence of familial searches currently varies throughout the world. The researchers say the UK is “the most prominent and longstanding advocate of the technique”, while the US states most actively pursuing the technique are California, Colorado, Virginia and Texas. The researchers revealed the success rate of the technique as reported in the UK (11-27%) and California (7%).

The researchers have determined that the technique not only has accuracy issues but also ethical issues: “privacy, equality and democratic accountability concerns”. The risk of misidentification means the real perpetrators could be getting away, while the immediate family of their distant relatives is wrongly targeted for further investigation.

And even if the technique is honed to become more accurate, the researchers say investigators may “widen their net of investigation to include more distant relations” if the source can’t be found among first-degree relatives. It has further been suggested that in the US the method may have a discriminatory effect, because DNA databases contain the profiles of certain racial minorities in disproportion to their presence in the population.