The genetics of palmar creases. A study in the inheritance of liability estimated from the incidence among relatives.

Six-hundred and fifty-nine Chinese children and 613 first degree relatives were studied with regard to four variations in the palmar creases: the simian crease, the Sydney line, the radial border termination of the thenar crease, and the distal border termination of the distal crease. With the exception of the Sydney line, these palmar crease variations were found to occur with significantly increased frequency in the parents of the propositi compared with 400 controls, indicating the presence of genetic factors in their embryogenesis. If the polygenic hypothesis is accepted, the very high heritability of liability (100%) to the radial border termination of the thenar crease is a further demonstration of the importance of the genetic contribution. Variations in the palmar creases thus cannot be totally explained away by early flexional folding in the skin of the developing hand.