Dermal ridge patterns are the result of the interaction of 2 embryologic processes: the formation and later regression of the volar pads between the eighth and twelfth week of gestation and dermal ridge differentiation at around the twelfth week of gestation. The size and shape of the volar pad at the time of ridge differentiation influences the ultimate ridge pattern: in general, if the pad is large, a whorl will be formed, whereas if the pad is small, a plain arch will be formed. A loop is an intermediate pattern. In Caucasians, the loop is the most common pattern, and the arch is a rare pattern comprising 4 to 5% of fingertip patterns in the population. Fingertip arches are more common in females than males (Reed et al., 2006). [from
OMIM]