The causes of psychological disorders are notoriously difficult to find. Even mental illnesses with significant genetic heritability can only be linked to small variations in hundreds of genetic regions. Depression has been one of the most difficult conditions to trace, and postpartum depression (PPD) even more so, since it occurs only in some mothers and only for a limited time. Researchers led by a University of North Carolina team are hoping to collect 100,000 DNA samples to find clues about PPD — a lofty goal, for sure, but they’ll have help from an unlikely source.

The researchers will use an iPhone app to recruit women who have experienced PPD and compare their DNA to that of women who have never had it in hopes of discovering linked genetic factors. Finding genetic markers could allow clinicians to better predict, diagnose, and treat the maternal mental illness, which affects about 1 in 7 women.

The app is called PPD ACT, and will be available free through Apple products as part of the company’s ResearchKit. It will ask users a series of questions about depression and anxiety after pregnancy to assess for postpartum depression. The team’s theory is that PPD may involve genes identifiable during or soon after pregnancy, so the DNA collected from these women would be especially useful.

“From a genetic standpoint, this is the right time biologically to do this,” Dr. Patrick F. Sullivan, director of the University of North Carolina’s Center for Psychiatric Genomes, told The New York Times. Sullivan will lead the project’s genetic analysis.

Women who score highly on the PPD scale will be asked if they would like to submit DNA. If they agree, they’ll be mailed a kit to donate saliva. The samples, though they require personal data like names and email addresses, will be encrypted once collected.

“Each will be individually genotyped for something like 600,000 genetic markers scattered throughout the genome,” Dr. Sullivan said. The million dollar question? “Are there regions of the genome where women with postpartum depression differ systematically from women without?”

Dr. Sullivan and some colleagues recently conducted a study that suggested PPD may be more heritable than general depression and could therefore be easier to study. Some researchers disagree — David Goldstein, director of Colombia University’s Institute for Genomic Medicine, suggested that PPD’s links to hormonal fluctuations and the emotional stress of having a child may indicate it is less likely to be genetic.