Fragile-X syndrome in Hawaii: a summary of clinical experience

Characterization of ultrasonic vocalizations of Fragile X mice

Fragile X Syndrome (FXS) is the leading form of inherited intellectual disability. It is caused by the transcriptional silencing of FMR1, the gene which codes for the Fragile X Mental Retardation Protein (FMRP). Patients who have FXS exhibit numerous behavioral and cognitive impairments, such as attention-deficit/hyperactivity disorder, obsessive compulsive disorder, and autistic-like behaviors. In addition to these behavioral abnormalities, FXS patients have also been shown to exhibit various deficits in communication such as abnormal sentence structures, increased utterances, repetition of sounds and words, and reduced articulation. These deficits can dramatically hinder communication for FXS patients, exacerbating learning and cognition impairments while decreasing their quality of life. To examine the biological underpinnings of these communication abnormalities, studies have used a mouse model of the Fragile X Syndrome; however, these vocalization studies have resulted in inconsistent findings that often do not correlate with abnormalities observed in FXS patients. Interestingly, a detailed examination of frequency modulated vocalizations that are believed to be a better assessment of rodent communication has never been conducted. The following study used courtship separation to conduct a detailed examination of frequency modulated ultrasonic vocalizations (USV) in FXS mice. Our analyses of frequency modulated USVs demonstrated that adult FXS mice exhibited longer phrases and more motifs. Phrases are vocalizations consisting of multiple frequency modulated ultrasonic vocalizations, while motifs are repeated frequency modulated USV patterns. Fragile X mice had a higher proportion of "u" syllables in all USVs and phrases while their wildtype counterparts preferred isolated "h" syllables. Although the specific importance of these syllables towards communication deficits still needs to be evaluated, these findings in production of USVs are consistent with the repetitive and perseverative speech patterns observed in FXS patients. This study demonstrates that FXS mice can be used to study the underlying biological mechanism(s) mediating FXS vocalization abnormalities.

Speech fluency in fragile X syndrome

The present study investigated the dysfluencies in the speech of nine French speaking individuals with fragile X syndrome. Type, number, and loci of dysfluencies were analysed. The study confirms that dysfluencies are a common feature of the speech of individuals with fragile X syndrome but also indicates that the dysfluency pattern displayed is not identical to developmental stuttering. To what extent the pattern of dysfluency in individuals with fragile X syndrome is syndrome specific is not yet clear.

Fluency disorders in genetic syndromes

The characteristics of various genetic syndromes have included "stuttering" as a primary symptom associated with that syndrome. Specifically, Down syndrome, fragile X syndrome, Prader-Willi syndrome, Tourette syndrome, Neurofibromatosis type I, and Turner syndrome all list "stuttering" as a characteristic of that syndrome. An extensive review of these syndromes indicated clients diagnosed with these syndromes do show evidence of nonfluency patterns, but not all would be considered stuttering. Many of the syndromes are marked by degrees of mental retardation that probably contribute to a higher than average prevalence of stuttering, as well as a higher than average prevalence of other fluency disorders (when compared to the population at large). An in-depth analysis of the available data indicates that some of these genetic syndromes show patterns of stuttering that may be indicative of only that syndrome (or similar syndromes) that can be differentially diagnosed from developmental stuttering. Among these patterns are the word-final nonfluencies noted in Prader-Willi syndrome; the presence of stuttering in the absence of secondary behaviors noted in Prader-Willi syndrome and; the presence of palilalia, word-final and word-medial nonfluencies, and word-medial and word-final nonfluencies in Tourette syndrome. Implications for future research are discussed in light of these findings.

EDUCATIONAL OBJECTIVES

The reader will be able to: (1) describe the various different genetic syndromes that are associated with fluency disorders; (2) describe the types of nonfluencies that are associated with the major types of genetic syndromes that have fluency disorders; (3) describe the behaviors that may assist in differentially diagnosing different types of speech characteristics associated with various genetic syndromes.

Articulation rate and vowel space characteristics of young males with fragile X syndrome: preliminary acoustic findings

PURPOSE

Increased speaking rate is a commonly reported perceptual characteristic among males with fragile X syndrome (FXS). The objective of this preliminary study was to determine articulation rate-one component of perceived speaking rate-and vowel space characteristics of young males with FXS.

METHOD

Young males with FXS (n = 38), developmental age (DA)-matched males (n = 21), and chronological age (CA)-matched males (n = 16) were audiotaped while engaged in spontaneous conversation and a picture-naming task. Articulation rate in syllables per second during intelligible utterances and vowel space area/dispersion measures were acoustically determined for each speaker.

RESULTS

Males with FXS did not articulate significantly faster than CA-matched males. Area and dispersion of the acoustic vowel space also were similar between the 2 groups. Males with FXS, however, used significantly shorter utterances and had a tendency to pause less often than CA-matched males. In addition, males with FXS exhibited greater intraspeaker variability of formants associated with the vowel /a/.

CONCLUSIONS

These preliminary findings suggest that articulation rate may not be a primary factor contributing to perceived speaking rate of males with FXS. Limitations of the study relative to speech production tasks and utterance intelligibility are discussed.

Genetic variation and evolutionary stability of the FMR1 CGG repeat in six closed human populations

In an attempt to understand the allelic diversity and mutability of the human FMR1 CGG repeat, we have analyzed the AGG substructure of this locus within six genetically-closed populations (Mbuti pygmy, Baka pygmy, R. surui, Karitiana, Mayan, and Hutterite). Most alleles (61/92 or 66%) possessed two AGG interspersions occurring with a periodicity of one AGG every nine or ten CGG repeats, indicating that this pattern is highly conserved in all human populations. significant differences in allele distribution were observed among the populations for rare variants possessing fewer or more AGG interruptions than the canonical FMR1 CGG repeat sequence. Comparisons of expected heterozygosity of the FMR1 CGG repeat locus with 30 other microsatellite loci, demonstrated remarkably similar levels of polymorphism within each population, suggesting that most FMR1 CGG repeat alleles mutate at rates indistinguishable from other microsatellite loci. A single allele (1 out of 92) was identified with a large uninterrupted tract of pure repeats (42 pure CGG triplets). Retrospective pedigree analysis indicated that this allele had been transmitted unstably. Although such alleles mutate rapidly and likely represent evolving premutations, our analysis suggests that in spite of the estimated frequency of their occurrence, these unstable alleles do not significantly alter the expected heterozygosity of the FMR1 CGG repeat in the human population.

Cognitive functioning and information processing of adult mentally retarded men with fragile-X syndrome

The present study describes cognitive skills and information processing strategies of mentally retarded fra(X) men. Fifty-eight fra(X) positive and 58 fra(X) negative adults, matched on sex, chronological age, length of institutionalisation, general cognitive level, and living conditions, were evaluated with the Bayley or McCarthy Scales of Mental Abilities. Mental ages were mostly situated in the severe mental handicap category and were found to be negatively influenced by chronological age. A relative strength in perceptual performance and non-verbal reasoning and a deficit in sequential information processing turned out to be typical of all mentally retarded subjects, irrespective of fra(X) or control status. Fra(X) adults could be significantly differentiated from control persons on the ground of a higher level of acquired knowledge because of better vocabulary and verbal-expressive skills. On the other hand, they were less able to imitate non-verbal patterns, had more difficulty with visual-motor integration and co-ordination, and applied less efficient general mental processing skills in solving new problems. The memory profile of fra(X) adults was strongly determined by the meaning and the complexity of the information that has to be reproduced. In this article the profile of cognitive strengths and weaknesses in the fra(X) group will be discussed and some general advice for training is suggested.

What is associated with the fragile X syndrome?

In addition to mental retardation (MR), fragile X[fra(X)] syndrome has been associated with a variety of other disorders. Despite earlier reports, it has been shown that MR fra(X) males are at no greater risk for autism than is any MR male. Therefore, studies in which fra(X) has been associated with behavioral, developmental, and psychopathological disabilities were examined to determine whether fra(X) individuals were at an increased risk for these dysfunctions as well. Psychiatric disorders among fra(X) individuals were found not to occur more frequently than in other individuals with cognitive deficits. It was also observed that hyperactivity and attention deficit disorder among MR fra(X) individuals do not occur more frequently than in other MR individuals. Pooled results from studies of cognitive profiles used to characterize fra(X) phenotypes also indicated that there are no consistent patterns in either males or females. Plausible explanations for a variable phenotype include allelic heterogeneity and pleitropy.

Autism is not associated with the fragile X syndrome

We provided a controlled test of the hypothesis that individuals with the Martin-Bell or Fragile X [fra(x)] syndrome are more autistic than mentally retarded control individuals. A sample of fra(x) individuals was obtained from the register of a clinical genetics unit and compared with mentally retarded control individuals selected from an assessment centre who were individually matched for age, sex, and IQ. A comparison of 45 pairs of fra(x) cases and control individuals on the DSM-III (R) criteria for autism and two standardized "instruments" for the assessment of autism (ABC and ADC) failed to find a higher prevalence of autism among fra(x) individuals. There was no statistically significant difference between fra(x) individuals and control individuals, and the mean differences on both the ABC and ADC scales were in the direction contrary to the hypothesis. An analysis of the study's statistical power suggested that it is unlikely the investigation failed to detect a large to medium difference between fra(x) individuals and control individuals in autistic behaviour. Subsidiary analyses of case-control differences showed that two autistic-like behaviours occurred at a higher rate among fra(x) individuals than other mentally retarded children, namely, gaze avoidance and hand flapping. These abnormalities may have misled clinicians into thinking that autism and fra(x) are associated.

Intelligence and cognitive profile in the fra(X) syndrome: a longitudinal study in 18 fra(X) boys

A longitudinal study of IQ and cognitive profile in 18 fra(X) positive boys is reported. At the time of diagnosis, four of the boys were mildly retarded, seven were moderately retarded, and five were severely mentally retarded. Intelligence was borderline in one child and normal in another. A decline in intellectual performance with age in the fra(X) syndrome indicated in previous studies was not confirmed and we review the reported data on this subject.

Fragile (X) syndrome: a study of the psychological profile in 23 prepubertal patients

In this study a further analysis of the psychological profile in the prepubertal fragile (X) (fra(X] male was performed. The results of the psycho-diagnostic examination of 23 fra(X) boys were compared to a control group of 17 males of the same age with 'non-specific' mental retardation. A number of important quantitative and qualitative differences were observed between the two groups. In the preschool age group the majority of fra(X) boys was mildly mentally retarded. In the school-age group, however, most boys were moderately to severely mentally retarded. This indication of a decline in intellectual performance with age in the fra(X) syndrome was confirmed by a longitudinal individual follow-up of seven fra(X) boys in this age group. In contrast to intellectual performance, appearance of the attention deficit disorder (or hyperkinesis), with its attendent overactivity and impulsiveness, decreases with age, and is independent of the intellectual level. Autistic behaviour was more frequently observed in the youngest fra(X) males, and was more pronounced in the moderately mentally retarded. In more than 50% of the boys of preschool age the association of hyperkinesis and autistic features was found. Language and speech development in the fra(X) syndrome is both symptomatic and specific. Beside a severe, global speech retardation, there are some distinct speech characteristics in the young fra(X) males such as rapid speech rhythm, speech impulsiveness and perseverative speech.

Fragile X and autism: a multicenter survey

We screened 183 autistic males for the fra(X) and found 24 (13.1%) to be positive. Adding the subjects of this study to those of 11 other surveys, of which 6 were positive and 5 were negative, a total of 614 autistic males have been screened. Overall 47 (7.7%) were positive. Based on this estimate and the prevalence of autism and fra(X), we estimate that 12.3% of fra(X) males are autistic. We have found that 17.3% of our fra(X) males were autistic and overall a 21.2% frequency has been reported, these higher figures are most likely due to biases in age and ascertainment. With an overall 7.7% frequency of fra(X) among autistic males and an estimated 12.3% of autism among fra(X) males, we conclude there is likely to be a significant association of fra(X) with autism. Because fra(X) appears to be the single most common cause of the condition, chromosomal testing is recommended for any autistic person with undiagnosed etiology.

Female relatives in families with the fragile X syndrome

Three problems--mental retardation, having retarded children, and fear of having retarded children--are described in women in families with the fragile X syndrome. The investigation of one family with a counselling dilemma is presented in detail.

A new X-linked mental retardation syndrome

We have studied a three-generation family with 11 moderately to severely retarded males and three mildly retarded females (presumably manifesting carriers). The patients have a phenotype different from that of all other previously described types of X-linked MR (XLMR). These include short stature, macrocephaly, "coarse" facial appearance including prominent forehead and supraorbital ridges, hypertelorism, broad nasal tip with anteverted nostrils, and thick lips. All postpubertal males had macroorchidism (volume greater than 25 ml). Chromosomes were normal including fragile X analysis. X-ray findings of skull, spine, and hands were normal. The intellectually normal relatives do not resemble their affected relatives except for increased head size and testicular size. These findings suggest a new variant of XLMR different from fragile X-linked MR, the Coffin-Lowry syndrome, and other XLMR conditions.