Palmar dermatoglyphics of dyslexia.

Palmar dermatoglyphic prints were taken of 261 dyslexics (173 males and 88 females) and compared against those of 707 controls (372 males and 335 females). Dyslexics of both sexes were found to exhibit greater complexity in terms of ridge count and pattern location than controls, particularly on the left hand. Specifically, both male and female dyslexics exhibited higher left a-b counts, wider atd angles on both palms, and higher frequencies of pattern in left interdigital area IV. Additionally, male dyslexics also had higher right a-b counts and greater frequency of pattern in the left hypothenar area. Dyslexics of both sexes were also found to have more distally located axial triradii, and investigation of bilateral asymmetry found dyslexics to exhibit more directional asymmetry than controls in the variable of a-b count, with the left value for both groups being greater than the right. It was concluded that the study evidenced strong support for the hypothesis that some causative factor relating to the development of dyslexia is operating during the time period in which dermatoglyphic features are formed. The relevance of these findings in terms of the Geschwind hypothesis and the possible importance of prenatal testosterone are discussed.