Fragile-X syndrome III: dermatoglyphic studies in males.

Dermatoglyphics of 39 males with the fragile-X syndrome were compared with those of 3 groups of control subjects; 497 school boys, 15 males with non-specific mental retardation, and 15 with Down syndrome. Compared with the control males, there was an increased frequency of radial loops, whorls, and arches on the fingers and of third interdigital patterns and abnormal creases on the hands, and a decreased frequency of ulnar loops and fourth interdigital patterns in the patients with the fragile-X syndrome. The mean a-b ridge count was lower than in controls and there were more patients than controls with an a-b ridge count less than 70. All of these differences were significant at p less than 0.01. There was no differences between patients and controls with respect to total ridge count on the fingers and the dermatoglyphics in other areas of the hands or feet. From this small study a preliminary index was developed that attempts to distinguish male patients with the fragile-X syndrome from normal male controls and males with non-fragile-X forms of mental retardation. The patterns on the left and right third fingers, the a-b ridge count, and the palmar creases were used in the index. Sixty-four % of patients with the fragile-X syndrome would be selected out if greater than or equal to + 0.5 was used as the criterion and 90% of these males would be expected to have the fragile-X chromosome.