Relationship between age and IQ among fragile X males: A multicenter study

Abstract

Longitudinal decline in IQ among fragile X males was reported recently. However, there are problems in retesting IQ that may affect scores. Two such factors are intertest time interval and score obtained on the first test. To determine the generality of IQ score changes, we examined 101 fragile X males from 6 centers. To ensure high test-retest reliability, only results from Stanford-Binet and Wechsler tests were used. Thus there were retest scores from 60 subjects. Test-retest reliability between first and last scores was very good (r = 0.85) and comparable to those seen in nonfragile X mentally retarded individuals. Also computed were z-scores of differences in IQ scores. The z-score differences were distributed about a mean at 1 SD below the expected zero value. Eighteen subjects showed statistically significant decreases in IQ, 6 showed statistically significant increases, while 5 showed the same scores. Z-score differences were not correlated with type of residence or elapsed intertest interval, but were negatively correlated with first score obtained, indicating a regression-to-the-mean effect. Using a multiple regression analysis, we found first score obtained, age tested, and age retested significant predictors of score differences, accounting for 19% of the total variance. These results suggest that factors previously identified as affecting retest scores have a smaller effect than originally thought. It is suspected that decline in IQ is associated with dynamic neurological processes and needs to be investigated further.

Adaptive behavior in the fragile X syndrome: Profile and development

“…It is evident that there is a stagnation in intellectual growth, confirming other research data in this area [Fisch et al, 1991;Hodapp et al, 1990;Wiegers et al, 19921. Despite this, self-help skills continue to grow with age at remarkable speed.…”

Screening for Fragile X Syndrome: Information Needs for Health Planners

“…31 However, IQ studies must be interpreted with caution as they are complicated by the use of different measures of intelligence and the presence of cognitive and behavioural problems. "…”

Longitudinal changes in IQ among fragile X males: Clinical evidence of more than one mutation?

“…Lachiewicz et d. [1987] and Hagerman et al [1989] found significant declines in IQ while Fisch et al [1991] found both significant increases and decreases. Although age has been identified as a salient factor in IQ decline, not all males appear to be so affected.…”

“…Moreover, factors unrelated to age were found to have a significant effect on standardized differences in IQ scores (Zdiff). For example, Fisch et al [1991] noted a significant regression-to-the-mean effect in test-retest scores. Fisch et al also observed that despite its longitudinal effect on cognitive development, age contributed only a small proportion to the overall variance in Zdiff scores.…”