Abstract

Indices for males with the fragile X [fra(X)] syndrome and for the female heterozygotes have been established. The indices were based on the increased frequencies of whorls and radial loops on the third digits of affected males and heterozygous females, increased frequency of arches on the third digits of the affected males, and an excess of low ab ridge counts and abnormal palmar creases, particularly the Sydney crease, in both sexes. The indices were calculated using the logN odds ratio based on the frequencies of the above dermatoglyphics and palmar creases in 47 males with the syndrome compared to 497 male controls and 36 heterozygous females compared to 493 female controls. The indices had similar distributions in males and females. Seventy per cent of males with the syndrome and 67% of female heterozygotes had an index greater than or equal to +0.5. Thirty-one per cent of female heterozygotes who had both the dermatoglyphic index calculated and their chromosomes examined under appropriate conditions for the fra(X) site had an index less than +0.5 and had less than 2% fragile sites (most had none). However when the two tests were considered together, only 4/35 (11%) of the heterozygotes would not have been identified using the two criteria. The data suggest that the dermatoglyphic index is a helpful adjunct test with chromosome analysis for the identification of fra(X) heterozygotes.