Fluctuating dermatoglyphic asymmetry in psychotic twins.

Fluctuating asymmetry of bilateral morphological traits is the result of prenatal developmental instability and has been shown to be greater in organisms having more homozygous genotypes (aabb vs. AaBb, for example). This expected increase in fluctuating asymmetry has been found among individuals having a high degree of liability for schizophrenia, as this disorder appears to have a polygenic basis. We tested the additional prediction that the greater genetic liability for schizophrenia necessary for concordance between twins should be associated with greater fluctuating asymmetry in twin pairs in which both twins are mentally ill compared to twin pairs in which one individual is normal. Our analysis of asymmetry for finger ridge counts from fingerprints of concordant and discordant pairs of twins supports this prediction and provides additional indirect support for the roles of polygenic transmission and prenatal epigenetic vulnerability in schizophrenia.