A comparison of speed and accuracy of motor speech behaviors in fragile X syndrome and nonspecific X-linked mental retardation

The purpose of this study was to examine the speed and accuracy of motor speech behavior in individuals exhibiting fragile X syndrome and individuals exhibiting nonspecific X-linked mental retardation (XLMR). Subjects were nineteen males between the ages of twelve years seven months and forty years nine months, with I.Q.’s representing a range of severe to borderline mental retardation.

Experimental methods involved performance of diadochokinetic rate for reduplicated and nonreduplicated syllables and three repetitions of a list of twelve multisyllabic words. Multisyllabic word errors were determined phonologically.

Results essentially indicated that fragile X males and nonspecific XLMR males do not represent different populations in terms of either performance and nonperformance on diadochokinetic syllable tasks or in terms of number and patterns of errors on multisyllabic word tasks. One nonspecific XLMR kindred of four brothers was thought to be unrepresentative of the population as they displayed disproportionately poorer performance on motor speech tasks in comparison to the rest of the sample.

A high degree of variability was noted in performance by the sample. Findings are discussed in relation to assertions made previously in the literature. The data do not support apraxia versus CNS immaturity as a diagnostic label.