A 15-item checklist for screening mentally retarded males for the fragile X syndrome

Abstract

A 15-item checklist, including physical and behavioral features frequently observed in fragile X syndrome, was used in a prospective study of 188 mentally retarded males in order to identify males at risk for this syndrome. Of the 188 males, 19 were found to have the fragile X syndrome, while the remaining 169 males had no recognizable cause of their mental retardation, including normal chromosomes. Significant differences (p less than 0.01) were found between mentally retarded males with and without the fragile X syndrome with increased hyperactivity; shorter attention span; more tactile defensiveness, hand-flapping, perseverative speech, and hyperextensibility; large ears and testes; higher frequency of simian creases or Sydney lines and plantar creases; and more positive family histories of mental retardation in the fragile X syndrome males. Multiple regression and discriminant analyses of the 188 males indicated several physical features were useful predictors for inclusion in the fragile X syndrome group. An overall correct classification rate of 93% was achieved based on 6 variables (plantar crease, simian crease, hyperflexibility, large testes, large ears, and a positive family history of mental retardation) that were entered into the discriminant equation. Therefore, our experience with a 15-item checklist suggests the potential of screening for the fragile X syndrome in mentally retarded males and that 6 of the 15 variables were particularly good predictors of this syndrome.

Fig. 1

Frequency of each checklist item on the mentally retarded males with and without the fragile X syndrome.

Fig. 2

Percentage of mentally retarded males with and without the fragile X syndrome assigned to each checklist score interval.

Fig. 3

The distribution of checklist scores for the mentally retarded males with and without the fragile X syndrome.

Fig. 4

Histogram depicting mentally retarded males with and without the fragile X syndrome classified by discriminant analysis. The discriminant equation is as follows: D = −1.848 + 0.902 (plantar crease) + 0.258 (family history of MR) + 1.182 (simian crease) + 0.396 (large testes) + 0.338 (large ears) + 0.477 (hyperextensibility). To calculate the discriminant value, insert the checklist score for each of the variables into the equation [score = 2 (if definitely present); 1 (if present in past or borderline); 0 (never present)].