A review found that physical hand biomarkers may be indicative of some mental disorders. These findings were published in The European Journal of Psychiatry.
An investigator at the University of Liverpool searched publication databases through 2020 for studies of dermatoglyphics (the study of skin markings or patterns on fingers, hands, and feet), digit ratio, and palmar crease in conjunction with mental illness. A total of 29 articles met the inclusion criteria.
Dermatoglyphics was investigated in 6 studies with 953 participants, digit ratio in 12 studies with 8736, and palmar crease in 11 studies with 13,030 participants. The dermatoglyphics studies related the biomarker with 4 mental illnesses, digit ratio with 9 illnesses, and palmar crease with 5 illnesses.
The studies of dermatoglyphics found relatively consistent relationships between mental illness and the biomarker, however, no 2 studies used the exact same biometric assessment. There were 3 studies that reported Cohen’s d, which showed medium to large effect sizes (d range, -0.59 to 0.99). Most of the studies of dermatoglyphics were conducted in India and as dermatoglyphics can vary with ethnicity, these findings may not be generalizable to other cultures.
For digit ratio, all studies had good methodological procedures and were determined to have minimal biases. Despite the study quality, the presented effect sizes were relatively inconsistent (d range, -1.3916 to 0.056). In general, findings from these studies were mixed and may be reflective of the potential for hormonal exposure in utero to affect digit ratio. Overall, there was evidence that digit ratio may be an indicator for attention-deficit/hyperactivity disorder, autism spectrum disorder, and alcohol dependence but little evidence to support other relationships.
Among the palmar crease studies, all reported consistent findings, in which abnormal palmar creases were more common among individuals with neurodevelopmental disorders. The review author did note that palmar crease was more prone to bias than the other 2 phenotypes due to the subjectivity in line classification systems.
This review was limited by the high heterogeneity among underlying studies.
The review author concluded, “The evidence of this review suggests that all 3 fields, dermatoglyphics, palmar creases, and digit ratio, can indicate mental disorders to varying degrees. Palmar crease research most consistently showed a correlation to mental illness although [it] did incur higher risks of bias than the other fields. Dermatoglyphics was the next most consistent, with studies generally finding similar significant results with some inconsistencies. Digit ratio was the least consistent and, as a single biometric assessment, was perhaps too limited to account for the complexity of psychological disorders to a degree of high magnitude.”
Rook L. Biomarkers of mental illness and the human hand: A systematic review. Eur Psychiatry. Published March 25, 2022. doi:10.1016/j.pnpbp.2020.109922