Fragile X syndrome

Fragile X syndrome is the most important X-linked etiology of mental retardation and developmental disability currently known. Accumulating evidence also indicates that male and female carriers of the fragile X genetic abnormality demonstrate a relatively specific pattern of psychiatric disturbance. Fragile X males frequently manifest behaviors from the autistic spectrum whereas females show dysfunction in social interaction, thought processes, and affective regulation. In this review, an overview of the fragile X syndrome is presented with a focus on the occurrence of particular neuropsychiatric characteristics in males and females. Relevant data from recent genetic and neurobiological research is also described. The ability to study individuals with a specific genetic cause of psychopathology such as fragile X syndrome makes this condition of particular interest to biological psychiatry.     

A family with Alport syndrome and psychosis

A family is described with a history of both hereditary nephritis (Alport syndrome) and chronic psychosis in multiple family members. Although the disorders do not segregate together in all cases, the finding of this family may provide a clue for the location of a psychosis gene. Alport syndrome has been mapped to the long arm of the X chromosome. Some studies also support a genomic locus on the X chromosome in at least some cases of manic-depressive disorder and schizophrenia.     

Phenotypic checklist to screen for fragile X syndrome in people with mental retardation

The development of a phenotypic checklist for identifying people with fragile X syndrome is described. The checklist was designed to identify people with developmental disabilities of unknown causes for molecular genetic testing for fragile X syndrome. The list consists of 28 items (7 on physical characteristics and 21 on behavioral features). Validation data were collected for 110 boys and men with fragile X syndrome and for 79 members of a control group, matched for CA, level of cognitive development, and social (mal)adaptation. On the basis of checklist results, those boys who are likely to be diagnosed as having fragile X syndrome can be identified. The screening list can be considered to be a consistent, reliable, and valid instrument.     

Decreased expression of the GABAA receptor in fragile X syndrome

After our initial discovery of under expression of the GABA(A) receptor delta subunit in a genome wide screening for differentially expressed mRNAs in brain of fragile X mice, a validated model for fragile X mental retardation syndrome, we analyzed expression of the 17 remaining subunits of the GABA(A) receptor using real-time PCR. We confirmed nearly 50% under expression of the delta subunit and found a significant 35%-50% reduction in expression of 7 additional subunit mRNAs, namely alpha(1), alpha(3), and alpha(4), beta(1) and beta(2) and gamma(1) and gamma(2), in fragile X mice compared to wild-type littermates. In concordance with previous results, under expression was found in cortex, but not in cerebellum. Moreover, decreased expression of specific GABA(A) receptor subunits in fragile X syndrome seems to be an evolutionary conserved hallmark since in the fragile X fly (Drosophila melanogaster) model we also found almost 50% under expression of all 3 subunits which make up the invertebrate GABA receptor, namely Grd, Rdl and Lcch3. In addition, we demonstrated a direct correlation between the amount of dFmrp and the expression of the GABA receptor subunits Rdl and Grd. Our results add evidence to previous observations of an altered GABAergic system in fragile X syndrome. Because GABA(A) receptors are the major inhibitory receptors in brain, involved in anxiety, depression, insomnia, learning and memory and epilepsy, processes also disturbed in fragile X patients, the well described GABA(A) receptor pharmacology might open new powerful opportunities for treatment of the behavioral and epileptic phenotype associated with fragile X syndrome.     

Fragile X-associated tremor/ataxia syndrome in sisters related to X-inactivation

Fragile X tremor/ataxia syndrome (FXTAS) is a recently described condition consisting of tremor, ataxia, parkinsonism, and executive dysfunction, presenting predominantly in male carriers of a fragile X mental retardation 1 premutation. In this report, we present premutation carrier sisters in whom severity of clinical signs correlated with a molecular pattern of X-inactivation favoring higher expression of the premutation allele. In these women with a common genetic background, we suggest that symptom severity may be dictated by X-inactivation, and thus a higher percentage of cells producing the premutation-containing mRNA result in increased toxicity and disease.     

Collaboration in referential communication: comparison of youth with down syndrome or fragile X syndrome

Referential communication was examined in youth with Down syndrome or fragile X syndrome in comparison to each other and to MA-matched typically developing children. A non-face-to-face task was used in which the participant repeatedly described novel shapes to listeners. Several dimensions of referential communication were especially challenging for the syndrome groups (i.e., they displayed below-MA performance), although there were differences in the dimensions that each syndrome group found to be most challenging. Independently assessed expressive language ability contributed to variations in referential performance, especially for participants with Down syndrome.     

Auditory evoked magnetic fields in adults with fragile X syndrome

Hyper-reactivity and anxiety to sensory stimuli have been described in patients with fragile X syndrome (FXS), and may be related to abnormal processing in afferent sensory pathways. We used magnetoencephalography (MEG) to measure auditory responses to pure tones in 11 adults with FXS and 11 non-FXS subjects. The amplitude for the N100m auditory evoked field component was significantly higher for patients with FXS than for subjects. FXS subjects also had less lateralized N100m anterior-posterior dipole locations. These data may suggest that more neurons are activated by acoustic stimuli in FXS, consistent with subjective experience of increased stimulus intensity. Anomalous cerebral lateralization may suggest an early critical window for effects on neocortical development of the fragile X mental retardation protein (FMRP) produced by the FMR1 gene in individuals with FXS.     

The fragile X syndrome

Males who possess the fragile X chromosome, a marker on the end of the X chromosome at position Xq27.3, have a distinct form of mental retardation, which has come to be known as the fragile X [fra(X)] syndrome. This X-linked syndrome is the most common Mendelian form of mental retardation. Males who inherit the fra(X) chromosome are usually moderately to severely retarded. There are also normal carrier men who are nonpenetrant for the mutation. They transmit the mutation to their daughters, who can have affected sons. The development of methods for detecting fra(X) in blood and amniotic fluid cells has allowed for population screening and prenatal diagnosis of the syndrome. New methods using DNA probes and restriction fragment length polymorphisms (RFLPs) are being applied to study the inheritance of fra(X). They have revealed apparent genetic linkage heterogeneity. Molecular studies to analyze the underlying mutation are underway to define the structural basis.     

The psychiatric phenotype in triple X syndrome: New hypotheses illustrated in two cases

Background: Triple X syndrome (47,XXX or trisomy X) is a relatively frequent cytogenetic condition with a large variety of physical and behavioural phenotypes.

Method: Two adult patients with a triple X karyotype are described.

Results: Their karyotype was unknown until some years ago. What these patients have in common is that they were diagnosed with a broader autism phenotype, they were sexually abused, they suffer from psychotic illness and they show challenging behaviour, suicidality and a decline in occupational capacity.

Discussion: These gene–environment interactions are discussed. Gene–environment interactions may explain the variety of behavioural and psychiatric phenotypes in triple X syndrome. Ongoing atypical development in adults is hypothesized.

Conclusions: Gene–environment interactions and ongoing atypical development in adults should be taken into account in research concerning the psychiatric phenotype of developmental disorders, especially those involving triple X syndrome.     

Klinefelter syndrome and associated Fragile-X syndrome

ABSTRACT. During screening of male individuals for Fragile-X syndrome in a residential facility for persons with mental retardation, the authors found a 21-year-old profoundly retarded man who displayed facial features and behaviour suggestive of Fragile-X syndrome. The chromosome analysis revealed 47, fra(X)(q27)fra(X)(q27)Y. His physically and intellectually normal sister had 14% of X chromosomes with a fragile site. Her two sons, who were subsequently examined, were found to have Fragile-X syndrome.
Thus, the identification of Fragile-X syndrome in the proband during the screening process of a large institution led to the investigation of the proband's family and the subsequent diagnosis of Fragile-X syndrome in the proband's two nephews. The ascertainment of the two affected boys permitted prompt introduction of early intervention and special education services. Genetic counselling of other at-risk family members was carried out.     

Neurological findings in patients with the fragile-X syndrome.

We report two brothers with previously unexplained mental retardation and seizures who had dysmorphic facial features, macro-orchidism, and a fragile site at the X chromosome. This recently described syndrome is the second most common chromosome aberration associated with mental retardation after Down's syndrome. In order to determine the prevalence of seizures and the frequency of specific neurological features, we studied a total of 17 patients with the fragile X syndrome. 41% had grand mal seizures; 41% had extensor plantar responses; 47% had hyperactive behaviour and 65% exhibited stereotypics; 59% had incoordination and 35% had blepharospasm. We emphasise the need for chromosome analysis of patients with unexplained mental retardation, specific phenotypic abnormalities, and large testes.     

A case of Turner syndrome with schizophrenia: Genetic relationship between Turner syndrome and psychosis

Abstract An 82-year-old woman with Turner syndrome and schizophrenia, and her 46-year-old daughter with schizophrenia are described. 45X/46XX chromosomal mosaicism was identified in the peripheral leukocytes of the mother, who showed several Turner dysmorphisms and cavum septi pellucidum in the brain. She had a normal reproductive life-span. The daughter resembled the mother in terms of schizophrenic symptoms, but she did not show any signs of Turner dysmorphism or chromosomal abnormality. The phenotype-karyotype relationship of Turner syndrome and the genetic relationship with psychosis are discussed.     

Familial X-linked mental retardation syndrome associated with minor congenital anomalies, macro-orchidism, and fragile X-chromosome

Three young males of Azorian origin who exhibited significant mental retardation, minor congenital anomalies, behavior disorders, and macro-orchidism were described. The chromosomal analysis revealed a fragile X chromosome in all three patients.     

Autism and the fragile X syndrome

The fragile X chromosome is an important factor in inherited mental retardation in males. It has also been reported that infantile autism is associated with fragile X. Recently, an article reported an examination of a small sample of autistic children in whom the fragile X chromosome was not found. Its authors concluded that if an association between fragile X and autism exists, it is infrequent. In the present study of 144 autistic male subjects, 18 were found to have the fragile X chromosome, supporting other (epidemiological) findings that the association between fragile X and autism occurs relatively frequently.     

Girl with partial Turner syndrome and absence epilepsy

This report describes a 16-year-old girl with short stature (-5 standard deviations), normal puberty, panic attacks, absence epilepsy, some stigmata of Turner syndrome, and a Madelung deformity. Routine chromosomal analysis revealed a female karyotype with one abnormal chromosome X, with the suspicion of additional material on the short arm. With fluorescent in situ hybridization and array-multiplex amplifiable probe hybridization methodology, a complex aberration was detected, with a deletion of the distal part of Xp22.33 (including the short-stature homeobox gene) and a duplication of Xp22.32-p22.12 proximal to the deleted segment. The deletion in our patient involves the Xp22.33 region. Two genes in this region may contribute to the patient's phenotype: short-stature homeobox, and visuospatial/perceptual abilities. The duplication in our patient involves the Xp22.12-p22.32 region, which, according to the Online Mendelian Inheritance in Man database, contains at least 93 genes, 49 of which are of unknown function. It is difficult to conjecture which gene overexpression in this region may have contributed to the phenotype of our patient. To our knowledge, this small, complex chromosome X aberration was not described previously.     

Initial diagnoses given to persons with the fragile X associated tremor/ataxia syndrome (FXTAS)

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a newly described disorder that occurs in premutation carriers of the fragile X mental retardation 1 (FMR1) gene. Fifty-six patients with FXTAS were given 98 prior diagnoses: most were in the categories of parkinsonism, tremor, ataxia, dementia, or stroke. Data from this study and others were used to develop guidelines for FMR1 diagnostic testing for FXTAS.     

Peripheral nervous system pathology in fragile X tremor/ataxia syndrome (FXTAS)

Fragile X tremor/ataxia syndrome (FXTAS) occurs in individuals with moderate CGG expansion of the fragile X mental retardation 1 (FMR1) gene and is associated with intranuclear inclusions in neurons and astrocytes. Although the neuropathologic findings in the brain and spinal cord were described, pathological features in the peripheral nervous system were not reported. Here, we report on novel neuropathological findings in the peripheral nervous system and especially in autonomic ganglia at autopsy in a man with FXTAS. In addition to the characteristic brain and spinal cord findings, typical intranuclear inclusions were identified in the ganglion cells of adrenal medulla, dorsal root ganglia, paraspinal sympathetic ganglia, myenteric ganglia of the stomach and subepicardial autonomic ganglion of the heart. Our findings indicate that FXTAS diffusely involves the central and peripheral nervous systems, which explains the protean neurological symptoms ranging from dementia to dysautonomia.     

Cyclic AMP metabolism in fragile X syndrome.

Cyclic AMP (cAMP) metabolism was studied in platelets from a series of 14 patients with fragile X syndrome (fra X) and 21 control individuals. 1-Isobutyl-3-methylxanthine was used to inhibit phosphodiesterase and thus measure cAMP production, prostaglandin E1 was used to assess receptor-mediated cAMP accumulation, and forskolin was used to directly stimulate the catalytic subunit. In patients with fra X, basal production was 63% of that of control subjects (p = 0.019). Prostaglandin E1- and forskolin-stimulated production were 61% (p = 0.039) and 56% (p = 0.012) of that of control subjects, respectively. cAMP production in 8 patients with fra X overlapped the control range, whereas measures of production in 6 patients formed a cluster with values lower than any of the 21 control subjects assayed, suggesting possible biochemical heterogeneity within patients with fra X. Results obtained from the group of patients with fra X suggest possible abnormal function or regulation of the catalytic subunit of adenylate cyclase in at least a subgroup of patients with fra X. Variability of biochemical findings in patients with fra X may reflect the known high variability of the clinical syndrome.     

Adult fragile X syndrome

Summary Fragile X syndrome [fra (X)] is currently accepted as the second most frequent chromosomal disorder associated with developmental disability. Although next to Down syndrome in frequency, no postmortem studies of confirmed adult cases had been reported.The autopsy examination of a 62-year-old, moderately retarded man with the fra (X) syndrome confirmed the preferential involvement of cerebral and testicular structures in this disorder.Dendritic spine abnormalities of the type observed in trisomic chromosomal disorders were associated with synaptic immaturity. Severe testicular hypogonadism accompanied bilateralmacro-orchidism, normal penis, and unilateral hydrocele. Valvular, articular, and testicular interstitial compartments showed normal histochemical staining characteristics for glycoproteins and lipids.     

Cutis verticis gyrata, mental retardation and Lennox-Gastaut syndrome: a case report

Cutis verticis gyrata (CVG) is an abnormality of the scalp characterized by the formation of furrows and folds which cannot be flattened by traction or pressure. Primary and secondary forms of CVG have been described. We report on a patient affected by cutis verticis gyrata, mental regression and Lennox-Gastaut syndrome (LGS). Serum hormonal levels, karyotype and X fragile studies were normal. Magnetic resonance imaging of the brain showed only atrophic changes. The etiology of primary CVG remains unknown as does its relation with LGS. Received: 29 March 2001 / Accepted in revised form: 2 June 2001