Dermatoglyphics are the dermal ridge configurations on the digits, palms and soles. They begin to develop about the thirteenth week of prenatal life as the foetal mounds on the digit tips, interdigital, thenar and hypothenar areas of the hand and the corresponding areas of the foot. The pattern formation is complete by the nineteenth week.
The patterns on the fingertips are of the three basic types, the arches, loops and whorls or mixtures of them. Fig. 35. The loops may be ulnar or radial loops. Fig. 36. The pattern frequencies vary somewhat with the side and sex, with females having slightly more arches and fewer whorls than males. Racial differences too exist with Orientals having a higher frequency of whorls than European-Americans. A triradius is a three way fork, a confluence of three ridge systems. Arches have no triradii, a loop has one and the whorl has two or more. A triradius is seen at the base of the palm, the axial triradius. This may be displaced distally in certain conditions. In the soles too patterns are defined but not so prominently, except in the hallucal region.
Arch Loop Whorl
The palmar creases are usually made up of proximal and distal transverse creases and a thenar crease. Fig. 37. A single distal transverse crease is called a Simian crease. Fig. 38. A proximal transverse crease is called a Sydney crease. Fig. 39. These are seen in 6% and 11% respectively of normal individuals, but are also associated with certain disorders.*
The prints are made using special ink pads and papers. As they are laid down fairly early in embryogenesis, and determined largely by the genotype, abnormal patterns are evidence of developmental disturbances. They are particularly useful in cases of Down syndrome. A few examples seen in genetic disorders follow.
Trisomy 21 Usually all are ulnar loops and Simian Creases in 50%.
Turner syndrome Predominance of whorls
47, XXY Excess of arches
Trisomy 13 Excess of arches and Simian creases in 60%
Trisomy 18 6 - 10 arches and Simian creases in 30%
Cri du Chat(5p-) Excess of arches and Simian creases in 90%