Age-related language characteristics of children and adolescents with fragile X syndrome

In addition to moderate-to-severe mental retardation (MR), the fragile X [fra(X)] mutation produces significant impediments in speech and language. Severe delays in speech and language have been demonstrated in both adult males and young individuals with the fra(X) mutation. Having observed longitudinal declines in IQ scores in young males with fra(X) and given the relationship between cognitive ability and language skill, we wanted to determine whether speech-language deficits in young males with fra(X) were age-related in ways comparable with those observed in cognitive deficits. We examined a small sample (n = 16) of children and adolescents, ages 6-17 years, using the Clinical Evaluation of Language Fundamental-Preschool (CELF-P). The CELF-P is used to evaluate language deficits in preschool children and assesses receptive and expressive language ability. It is standardized for children ages 3-7 years and provides age-normed standard scores. To evaluate changes in language scores, we converted raw scores into age-equivalents. Results indicate that males with fra(X) have significantly lower age equivalent scores compared with females. A cross-sectional analysis of males' age-equivalent scores reveals that a plateau is reached at approximately 48 months. Our findings suggest that, as with IQ and adaptive behavior scores, language development in young, fully mutated fra(X) individuals appears to reach a plateau as they age.     

Lack of association between mutation size and cognitive/behavior deficits in fragile X males: A brief report

Previously, researchers reported molecular-neurobehavioral or molecular-cognitive associations in individuals with fra(X) (fragile X) mutation. However, not all investigators have noted molecular-behavioral relationships. Consequently, we examined prospectively 30 fra(X) males age 3–15 years from four testing sites to determine whether there was a relationship between mutation size and degree of either cognitive or adaptive behavior deficit. To measure cognitive abilities, all individuals were administered the Stanford-Binet (4th edition) IQ test. To evaluate adaptive behavior (DQ) skills, all individuals were assessed using the Vineland Adaptive Behavior Scale. To determine fra(X) status, genomic DNA from all individuals was extracted and digested with EcoRI and EagI restriction enzymes. Southern blots were prepared and hybridized with the pE5.1 probe. The Pearson correlation coefficient between full mutation size and composite IQ score revealed a nonsignificant, near-zero association (r = 0.06; P > .76). The Pearson coefficient between mutation size and DQ also showed a nonsignificant, near-zero association (r = 0.06; P > .73). We conclude that while fra(X) mutation produces cognitive and behavior deficits in males who inherit the defective gene, there is no relationship between mutation size and degree of deficit. © 1996 Wiley-Liss, Inc.     

Longitudinal assessment of adaptive and maladaptive behaviors in fragile X males: growth, development, and profiles

As young fully mutated fragile X [fra(X)] males age, cognitive levels (IQ scores) and adaptive behavior levels (DQ scores) decline. Given the variable behavioral profiles reported previously, we wondered whether changes in specific attributes of adaptive behavior are related to declines in composite adaptive behavior levels. We also examined maladaptive behavior to determine if changes are related to age. Therefore, we evaluated three areas of adaptive behavior, as well as maladaptive behavior, in 28 fully mutated fra(X) males, ages 4-14 years. To develop a profile of adaptive behavior, we analyzed nine subscale scores from the Vine-land Adaptive Behavior Scale (VABS). To assess maladaptive behavior, we graded part I of the VABS Maladaptive Behavior Scale. Subjects were sorted into three age cohorts, according to their initial test age: younger than 6 years; 6 to 9 years; older than 9 years. Results indicate that, in all age groups, the communications domain is the most severely impacted compared with either the socialization domain or daily living skills and that, in all age groups, the socialization domain is a relative strength compared with either the communications domain or daily living skills. The youngest cohort manifested significant increases in age-equivalent community living skills. Significant differences in age-equivalent scores between cohorts were observed in written language and play skills. Maladaptive behavior scores were available from cross-sectional data only. Twenty males (74%) showed significantly higher maladaptive scores than expected from other children their age. Our data analysis also revealed a moderate and significant negative correlation between maladaptive behavior levels and age (r = -0.54; P < 0.01). Curiously, adaptive and maladaptive behaviors did not correlate with each other.     

Cognitive-behavioral profiles of females with the fragile X mutation

The fragile X (FRAXA) mutation is typically manifested as either a full mutation (FM) or premutation (PM), and is often associated with some form of learning impairment. The study by Lachiewicz et al. in this issue suggests that females with the FM or PM exhibit a specific profile of strengths in verbal abilities and significant weaknesses in quantitative skills. We examined 17 females with either the FM or PM using a standard cognitive-behavioral battery consisting of the Stanford-Binet (4th Edition; SBFE) and the Vineland Adaptive Behavior Scale (VABS). Although we found the expected differences in composite IQ scores and adaptive behavior composite scores (DQ) between FM and PM females, we found no significant differences between verbal and quantitative reasoning in either group.     

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

Longitudinal changes in IQ among mentally retarded (MR) fragile X [fra(x)] males have been reported previously. While age is associated with decline in IQ, not all males are so affected. This suggests that there may be more than one subtype of affected fra(X) male. Therefore, we examined the distribution of standardized difference scores (Zdiff) in IQ to determine if subjects were from an admixture of at least 2 populations. Cluster analysis of Zdiff scores was used to partition subjects into 2 groups. Goodness-of-fit tests indicated that scores were more likely to come from an admixture. Discriminant functions (DF) were calculated to determine predictive validity of Zdiff scores. To eliminate the effect of skewing, a power transform was applied to Zdiff scores and DFs recomputed. Zdiff and transformed scores provided similar results. The mean and variance for one group showed no differences in test-retest scores as would be expected from examining any population while the mean for the second group indicated significant decline in IQ nearly 4 standard errors below the first test score. These results suggest that there may be clinical evidence for 2 types of fra(X) mutation: One which causes MR but is static, and a second mutation which causes MR but is dynamic and contributes to an apparent longitudinal decline in cognitive function.     

Individual variation and specific cognitive deficits in the fra(X) syndrome

Mental retardation has been associated with fra(X) but comprehensive psychological evaluation has rarely been applied to 2 major behavioral questions 1) the extent of individual variation in IQ among fra(X) males and the possibility of some fra(X) males being of normal IQ; and 2) whether there is a depression in general IQ or whether specific abilities are impaired. The problems of developing an effective battery of tests for assessing fra(X) are discussed. These questions were examined in 54 individuals, comprising fra(X) males, their obligate carrier mothers and those sisters shown to have the fra(X). Among noninstitutionalised males nonverbal IQ as measured on a Block Design test ranged from 100 to 0, and vocabulary scores while generally higher, ranged from 79-33. The males scored low on a digit span memory task, while performance on a memory of objects task was adequate. Despite lower overall scores, a similar pattern and variability emerged in institutionalised males. Daughters were extremely variable in performance and the mothers performed much better, supporting the view that women who have children are a selected subset of fra(X) syndrome individuals. The performance of one male is discussed in detail. His vocabulary and nonverbal IQ scores were normal, despite his having other specific cognitive deficits. The pattern of abilities and behavior seen in fra(X) may result in an overestimation of intelligence and underestimation of penetrance when based on clinical impressions rather than formal psychological assessment. The implications of this for molecular and for population genetic approaches to fra(X) are discussed.     

A. Donald Merritt,M.D.

Mental retardation has been associated with fra(X) but comprehensive psychological evaluation has rarely been applied to 2 major behavioral questions 1) the extent of individual variation in IQ among fra(X) males and the possibility of some fra(X) males being of normal IQ; and 2) whether there is a depression in general IQ or whether specific abilities are impaired. The problems of developing an effective battery of tests for assessing fra(X) are discussed. These questions were examined in 54 individuals, comprising fra(X) males, their obligate carrier mothers and those sisters shown to have the fra(X). Among noninstitutionalised males nonverbal IQ as measured on a Block Design test ranged from 100 to 0, and vocabulary scores while generally higher, ranged from 79–33. The males scored low on a digit span memory task, while performance on a memory of objects task was adequate. Despite lower overall scores, a similar pattern and variability emerged in institutionalised males. Daughters were extremely variable in performance and the mothers performed much better, supporting the view that women who have children are a selected subset of fra(X) syndrome individuals. The performance of one male is discussed in detail. His vocabulary and nonverbal IQ scores were normal, despite his having other specific cognitive deficits. The pattern of abilities and behavior seen in fra(X) may result in an overestimation of intelligence and underestimation of penetrance when based on clinical impressions rather than formal psychological assessment. The implications of this for molecular and for population genetic approaches to fra(X) are discussed.     

A controlled study of longitudinal IQ changes in females and males with fragile X syndrome

The aim is this study is to compare the longitudinal changes in IQ scores of females and males with fragile X syndrome and controls and to assess the impact on IQ of molecular variations of the FMR-1 gene in males. Medical records from the child development unit at a university-affiliated children's hospital were retrospectively reviewed. Chart review yielded 35 males with fragile X (19 with a fully methylated full mutation, 9 with a mosaic pattern, and 7 with a partially unmethylated full mutation) 16 females with fragile X and a full mutation, 9 female controls, and 9 male controls who had repeated standardized IQ testing separated by 7 months to 13 years. The differences between the first and last IQ scores from the same IQ test were compared by t tests and subsequently by analysis of variance. Overall, a significant IQ decline was seen in 10/35 (28%) of fragile X males, 0/9 (0%) of control males, 6/16 (36%) of fragile X females, and 1/9 (11%) of control females. The initial t tests and analysis of variance showed a significant difference in IQ (p = 0.02) between fragile X males and control males but did not show a significant difference between males and females with fragile X syndrome or between fragile X and control females. When an analysis of covariance was carried out with the initial IQ as a covariable, a significant difference persisted between fragile X and control males, with a greater IQ decline in fragile X males. There were limitations in using the same IQ test. A comparison among the molecular subgroups of males yielded a significant IQ decline in 3/9 (33%) of mosaic males, 6/19 (32%) of fully methylated full mutation males, and 1/7 (14%) of partially methylated full mutation males. An analysis of covariance using the initial IQ and the intertest interval as covariables demonstrated significant differences between the fragile X molecular subgroups and the controls. Our findings show that a substantial percentage of both male and female fragile X patients and female control patients demonstrated significant IQ decline. There was a significant differences in the IQ change between fragile X and control males. There were no significant differences between fragile X and female controls. There were also significant differences in IQ decline among males with different molecular patterns compared with controls. Males with a mosaic pattern versus control males had the most significant decline of the molecular subtypes. Although the numbers were limited, there was no significant IQ decline in males with less than 50% methylation of the full mutation. This suggests that a small amount of FMR-1 protein production, which is often seen in males with less than 50% methylation, protects against significant IQ decline. © 1996 Wiley-Liss, Inc.     

Cognitive profiles and the spectrum of clinical manifestations in heterozygous fra (X) females

We investigated the possibility that fra(X) heterozygotes had a distinct or specific set of mental deficits ("cognitive profile") which would allow for accurate diagnosis. Wechsler Intelligence Scale for Children-Revised (WISC-R) subtest scores obtained on 8 fra(X) school age girls were compared with similar scores obtained on 8 "learning-disabled" non fra(X) girls matched on the basis of Full Scale IQ (FSIQ). The Block Design subtest score was significantly lower in fra(X) girls. In a larger sample of 22 fra(X) females, a characteristic combination of low Arithmetic, Digit Span, and Block Design subtest scores was observed. The mean discrepancy between these 3 subtest scores from the total Verbal or Performance subtest means was significant for the fra(X) group but not for a comparison group of 20 learning-disabled females. Verbal IQ (VIQ) and Performance IQ (PIQ) discrepancy was not significant in fra(X) females. Percent fra(X) positive cells was negatively correlated with VIQ and FSIQ but not with PIQ.     

The fragile X syndrome in a large family. II. Psychological investigations.

Intelligence levels and intelligence profiles were investigated in 52 members of a large family with the fragile X syndrome. The mental abilities were evaluated by the three Wechsler intelligence tests (WAIS, WISC-R, and WPPSI). Chromosomal and psychological data were then compared. In 22 non-retarded fra(X) negative family members, a mean IQ of 102 was found (males 97, females 106). Eleven non-retarded carrier females had IQs between 70 and 110 (mean 86.8), which is 20 points below the mean of normal women (alpha = 0.01). One non-retarded male with 6% fra(X) positive cells had an IQ of 98. His intelligence profile closely resembled the profile in the non-retarded female carriers. The highest IQ in the group of retarded males was 31. The mentally retarded females scored IQs between 26 and 41. In male and female patients verbal intelligence substantially exceeded performance abilities. There was a considerable gap between the highest IQ in the group of retarded females and the lowest IQ in the group of non-retarded carriers (41 and 71 respectively) and a considerable overlap was found between the IQ levels of the non-retarded carriers and normal women.     

Cognitive profiles associated with the fra(X) syndrome in males and females

Twenty-three fragile X [fra(X)] males (mean IQ 50, mean age 10 years) and 11 fra(X) females (mean IQ 84, mean age 11.3 years) were administered the Stanford-Binet Intelligence Scale, 4th ed. (S-B). The cognitive profiles generated from the S-B indicated a pattern of subtest strengths and weaknesses that was similar for both groups. Consistent weaknesses in both groups were found in quantitative skills and short-term memory recall for visually presented, abstract stimuli, whereas a consistent strength was observed for short-term memory recall of visually presented, meaningful stimuli. Strengths in verbal labeling and comprehension and deficits in spatial visualization and visual-motor coordination were identified by the S-B for the male group but not for the female group. Fragility in the female group was negatively correlated with the S-B score for the short-term memory area and the combined S-B scores for the verbal reasoning and quantitative reasoning areas. The specific, S-B-identified cognitive strengths and weaknesses associated with the fra(X) condition are potentially useful indicators for investigation of specific cognitive process deficits associated with the fra(X) condition and the design of appropriate educational interventions for fra(X) children.     

Cognitive-behavioral features of children with Wolf-Hirschhorn syndrome: preliminary report of 12 cases

As a subset of genetic abnormalities, subtelomeric deletions have been found in 7-10% of individuals with mental retardation (MR). One subtelomeric deletion, Wolf-Hirschhorn syndrome (WHS), causes mild to severe MR, but the cognitive-behavioral features of individuals with WHS have not been studied systematically. To that end, we administered a comprehensive cognitive-behavioral battery to 12 children with WHS, ages 4-17 years, who also had some expressive language. Using the Stanford-Binet (4th Edition), we found cognitive deficits ranged from mild to severe, with mean IQ = 44.1. Interviewing parents with the Vineland Adaptive Behavior Scales, we found mean adaptive behavior score (DQ) = 37.3, with females exhibiting slightly higher scores than males. Cognitive profiles indicated relative strengths in Verbal and Quantitative Reasoning. Adaptive behavior profiles noted significant relative strengths in the Socialization Domain. These cognitive-behavioral profiles differed from children with other subtelomeric deletion syndromes, 2q37 or 8p23. Attention deficits and hyperactivity (ADHD) were observed in 7/12 (58%) of the children we tested. One child attained a score on the Child Autism Rating Scale (CARS) suggestive of mild autism. We conclude that different genetic disorders, which cause MR, produce diverse cognitive-behavioral profiles. Consequently, cognitive-behavioral profiles of children with MR need to be assessed more comprehensively.     

Fragile (X) X-linked mental retardation I: Relationship between age and intelligence and the frequency of expression of fragil (X)(q28)

Members of eight Saskatchewan families with fragile (X) X-linked mental retardation were studied in an attempt to relate frequency to age and intelligence. The mean IQ of 37 affected men was 35 (range 10–66). The mean IQ of 32 carriers was 88 (range 57–119), and the mean IQ of 13 females who remain at risk for being carriers, have no affected sons, and who failed to demonstrate the fra(X) was 100 (range 78–126). We demonstrated a significant inverse relationship between age and frequency of the fra(X) in carriers and in affected males. However, we demonstrated a more highly significant inverse relationship between frequency of the fra(X) and IQ in carriers but to a lesser extent in affected males. Of 32 carriers, only 3 (9.4%) did not demonstrate the fra(X) after addition of 5-fluoro-2′-deoxyuridine (FUdR) to the folic acid and thymidine-reduced culture medium. From these data we would recommend that chromosome studies in individuals at risk for fra(X) X-linked mental retardation be carried out at the youngest age and that the addition of FUdR to culture medium is useful in carrier identification. It is clear that, in at least the carriers, a lower expression of the fra(X) is highly significantly correlated to higher intelligence.     

Methylation and mutation patterns in the fragile X syndrome.

Chromosomes carrying the mutation causing the fragile X [fra(X)] syndrome have been shown to have an unstable DNA sequence close to or within the fragile site. The length variation is located within a DNA fragment containing a CGG trinucleotide repeat which is unstable in both mitosis and meiosis. We have used the probe StB12.3 from the region to analyze the mutations and the methylation patterns in 21 families segregating for the fra(X) syndrome. Among 40 fra(X) males all showed an abnormal pattern. The normal 2.8 kb band was absent in 36 individuals and replaced by a heterogeneous smear of larger size. The remaining four were shown to be "mosaics" with the presence of both mutated, unmethylated and mutated, methylated fragments. We found four normal transmitting males, one which was a great-grandson of another normal transmitting male indicating that the pre-mutation can remain stable through two meioses in the female. In nine fra(X) positive females the abnormal pattern consisted of a smear, usually seen in affected males, in addition to the normal bands. Five of these females were mentally normal. Of clinical importance is the prediction of mental impairment in females. We suggest that this is not made by the detection of the full mutation alone, but rather by the degree of methylation of the normal X chromosome. Our results suggest that difference of clinical expression in monozygotic twins may be correlated with difference in methylation pattern. Six out of 33 fra(X) negative females at risk were diagnosed as carriers. Our observations indicate that molecular heterogeneity is responsible for variable expression of the fra(X) syndrome in both males and females.     

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

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.     

An assessment of the use of flanking DNA markers for fra(X) syndrome carrier detection and prenatal diagnosis

One hundred and three individuals in 11 unrelated families with the fragile-X [fra(X)] syndrome were tested for polymorphisms identified by probes flanking the fra(X) site at Xq27.3. Two probes distal and 2 proximal to the fra(X) site were used. Thirteen known female carriers were analyzed retrospectively. DNA markers gave probabilities of carrying the mutation of 99% in 1 female, 89% in 8 females, and 10-55% in the other 4 females. We also estimated the probability of having inherited the mutation for 16 individuals of unknown fra(X) status using DNA markers and corrections for incomplete penetrance. The DNA marker test gave risks for females of 1-6% (7 females), 15% (1 female), and 97% (1 female). In males the risks were 1-3% (6 males) and 91% (1 male). In 3 families, DNA marker data were used to calculate probabilities of greater than or equal to 98.5% that transmission of the fra(X) mutation had occurred through normal males. In the retrospective studies, only 1 of 7 retarded males could have been diagnosed prenatally as having the fra(X) mutation with a probability of 99%. DNA marker analysis was uninformative in 5 of these males. When fra(X) carrier status cannot be established by chromosome analysis, DNA marker studies provide an alternative test that can be used to calculate individual risks more precisely. However, linkage analysis of the probe loci in these 11 families suggests that the recombination frequency between the fra(X) locus and the factor IX gene (F9) and DXS52 may be greater than previously suggested. Until the true recombination frequencies are established and the question of heterogeneity among families is fully analyzed, caution in using DNA markers as a predictive test is advised.     

FMRP expression as a potential prognostic indicator in fragile X syndrome.

Absence or deficit of FMR1 protein (FMRP) resulting from methylation of full mutation genes is the fundamental defect in fragile X syndrome. We used FMRP immunocytochemistry and detailed phenotypic assessment to investigate the relationship between degree of FMRP expression and the broad clinical spectrum of impairment in 80 individuals affected with fragile X syndrome. FMRP expression correlated with IQ in mosaic males (P=0.043), males with a partially methylated full mutation (P=0.0005), and females with a full mutation (P=0.046). In the females, FMRP expression also correlated with the number of fragile X physical features (P=0.0003). Even modest deficits in FMRP result in some manifestations of fragile X syndrome. In this initial study of 53 males, FMRP expression testing had a very high positive predictive value (100%, confidence interval of 29-100%) for a nonretarded IQ among males with expression of FMRP in > or = 50% of lymphocytes (3 males), suggesting that FMRP expression may have potential as a prognostic indicator in males with fragile X syndrome.     

Strengths and weaknesses in the cognitive profile of fra(X) patients

In this paper we present data on the cognitive abilities analyzed by systematic, standardized psychometric testing in 18 fra(X) boys who participated in a multicenter, longitudinal study. In the majority of the patients no significant differences were found between verbal and performance intelligence. Higher performance IQ than verbal IQ was found primarily in higher functioning fra(X) males, indicating a possible effect of level of functioning on the direction of verbal-performance IQ differences. Subtest-analyses showed lowest performances in Number Concept and Arithmetic Skills, whereas better performances were reached in Object Assembly and Picture Completion. These data are discussed and compared with the results in previous studies reported up to now.     

Biological and environmental contributions to adaptive behavior in fragile X syndrome

Fragile X syndrome is the most common cause of inherited developmental disability. The purpose of the present study is to understand how both biological and environmental influences affect the development of adaptive behavior in children with fragile X. In-home assessments were conducted on 120 children (80 boys and 40 girls) with the fragile X full mutation and their unaffected siblings (58 boys and 62 girls). Hierarchical multiple regression analyses were utilized. Independent variables included biological or demographic variables specific to the child (age, gender, full-scale IQ, and FMRP percentage), as well as factors specific to his/her environment (household income, home environment, maternal psychopathology, and effectiveness of educational/therapeutic services). Results of these analyses showed that for both boys with fragile X and the control sibling group, adaptive behavior was predicted by IQ, age, gender, and home environment. For girls with fragile X, adaptive behavior was most strongly associated with IQ. Adaptive behavior was not significantly associated with FMRP in boys or girls with fragile X. By examining the relative influences of biological and environmental factors on adaptive behavior in children with fragile X, we begin to lay the foundation for the development of more specific treatment studies in children with this disorder.