Hair Whorl

Whether the whorl in the scalp hair of the occipital area shows clockwise or counterclockwise rotation is genetically determined. Bernstein (1946) suggested that clockwise direction is dominant to counterclockwise direction. Brewster (1925) reported a family with double whorls or double crown. Lauterback and Knight (1927) described 3 crowns in 1 subject, 1 of which was conspicuous in the frontal area. Frontal 'cowlicks' are usual in the FG syndrome (Thompson et al., 1985). Sharma (1987) found a possible association between twinning and double occipital hair whorls; such was found in 25 of 244 twins, but in only 4 of 166 singletons.

Klar (2003) provided evidence for a link between handedness (139900) and the orientation of hair whorls on the scalp, suggesting the possibility that the same system that patterns hair may also play a role in left-right asymmetry in the brain. In a sample of the general population, consisting of mostly right-handers (RH), he found that 42 (8.4%) of 500 individuals showed counterclockwise whorl rotation. Non-right-handers (NRH, i.e., left-handers and ambidextrous) displayed a random mixture of clockwise and counterclockwise swirling patterns. Confirming this finding, in another independent sample of individuals chosen because of their counterclockwise rotation, half were found to be NRH. Klar (2003) stated that these findings of coupling in RH and uncoupling in NRH unequivocally established that these traits develop from a common genetic mechanism. Another finding, concerning handedness of the progeny of discordant monozygotic twins, suggested that lefties are 1 gene apart from righties. Together, these results suggested that a single gene controls handedness, whorl orientation, and twin concordance and discordance, and that neuronal and visceral forms of bilateral asymmetry are coded by separate sets of genetic pathways.

Hair whorls and other macroscopic hair patterns are found in a variety of mammalian species, including humans. Guo et al. (2004) showed that the frizzled-6 gene (FZD6; 603409) controls macroscopic hair patterning in the mouse. They found that Mfz6 is expressed in the skin and hair follicles and that targeted deletion of the Mfz6 gene produced stereotyped whorls on the hind feet, variable whorls and tufts on the head, and misorientation of hairs on the torso. Embryo chimera experiments implied that Mfz6 acts locally to control or propagate the macroscopic hair pattern and that epithelial cells rather than melanocytes are the source of Mfz6-dependent signaling. The Mfz6 phenotype strongly resembled the wing-hair and bristle patterning defects observed in Drosophila 'frizzled' mutants. These data implied that hair patterning in mammals uses a FZD6-dependent tissue polarity system similar to the one that patterns the Drosophila cuticle.