Elizabeth Berry-Kravis

Fragile X premutation tremor/ataxia syndrome: molecular, clinical, and neuroimaging correlates.

We present a series of 26 patients, all >50 years of age, who are carriers of the fragile X premutation and are affected by a multisystem, progressive neurological disorder. The two main clinical features of this new syndrome are cerebellar ataxia and/or intention tremor, which were chosen as clinical inclusion criteria for this series. Other documented symptoms were short-term memory loss, executive function deficits, cognitive decline, parkinsonism, peripheral neuropathy, lower limb proximal muscle weakness, and autonomic dysfunction. Symmetrical regions of increased T2 signal intensity in the middle cerebellar peduncles and adjacent cerebellar white matter are thought to be highly sensitive for this neurologic condition, and their presence is the radiological inclusion criterion for this series. Molecular findings include elevated mRNA and low-normal or mildly decreased levels of fragile X mental retardation 1 protein. The clinical presentation of these patients, coupled with a specific lesion visible on magnetic resonance imaging and with neuropathological findings, affords a more complete delineation of this fragile X premutation-associated tremor/ataxia syndrome and distinguishes it from other movement disorders.

Advances in the Treatment of Fragile X Syndrome

The FMR1 mutations can cause a variety of disabilities, including cognitive deficits, attention-deficit/hyperactivity disorder, autism, and other socioemotional problems, in individuals with the full mutation form (fragile X syndrome) and distinct difficulties, including primary ovarian insufficiency, neuropathy and the fragile X-associated tremor/ataxia syndrome, in some older premutation carriers. Therefore, multigenerational family involvement is commonly encountered when a proband is identified with a FMR1 mutation. Studies of metabotropic glutamate receptor 5 pathway antagonists in animal models of fragile X syndrome have demonstrated benefits in reducing seizures, improving behavior, and enhancing cognition. Trials of metabotropic glutamate receptor 5 antagonists are beginning with individuals with fragile X syndrome. Targeted treatments, medical and behavioral interventions, genetic counseling, and family supports are reviewed here.

A pilot open-label single-dose trial of fenobam in adults with fragile X syndrome

Objective: A pilot open label, single dose trial of fenobam, an mGluR5 antagonist, was conducted to provide an initial evaluation of safety and pharmacokinetics in adult males and females with fragile X syndrome (FXS). Methods: Twelve subjects, recruited from two fragile X clinics, received a single oral dose of 50–150 mg of fenobam. Blood for pharmacokinetic testing, vital signs and side effect screening was obtained at baseline and numerous time points for 6 h after dosing. Outcome measures included prepulse inhibition (PPI) and a continuous performance test (CPT) obtained before and after dosing to explore the effects of fenobam on core phenotypic measures of sensory gating, attention and inhibition. Results: There were no significant adverse reactions to fenobam administration. Pharmacokinetic analysis showed that fenobam concentrations were dose dependent but variable, with mean (SEM) peak values of 39.7 (18.4) ng/ml at 180 min after the 150 mg dose. PPI met a response criterion of an improvement of at least 20% over baseline in 6 of 12 individuals (4/6 males and 2/6 females). The CPT did not display improvement with treatment due to ceiling effects. Conclusions: Clinically significant adverse effects were not identified in this study of single dose fenobam across the range of dosages utilised. The positive effects seen in animal models of FXS treated with fenobam or other mGluR5 antagonists, the apparent lack of clinically significant adverse effects, and the potential beneficial clinical effects seen in this pilot trial support further study of the compound in adults with FXS.

Epigenetic Modification of the FMR1 Gene in Fragile X Syndrome Is Associated with Differential Response to the mGluR5 Antagonist AFQ056

An antagonist for the metabotropic glutamate receptor may improve symptoms in patients with fragile X syndrome whose FMR1 promoters are fully methylated. A Methylation Marker for Fragile X Syndrome Through the practice of meditation, students of Eastern philosophies are taught to turn down the noise to find the silence within. But for patients suffering from fragile X syndrome, it is the silence within that turns up the noise. In this disorder, a defect in the fragile X mental retardation 1 gene (FMR1) silences its expression, which gives rise to myriad molecular changes, most notably a turning up of signaling through the metabotropic glutamate receptor mGluR5. This noisy signaling pathway contributes to the cognitive deficits and differences that first become apparent in patients during childhood, and currently these symptoms are treatable only with supportive behavioral measures. But in mice and fruit flies that carry the same genetic defects as patients and also show enhanced glutamate receptor signaling and behavioral problems, administration of an mGluR5 antagonist improves the symptoms. Jacquemont et al. have now treated a group of 30 fragile X patients with such an antagonist. Not all subjects showed improvement, but an analysis of those who did revealed that the promoter of the FMR1 gene in drug-responsive patients is fully methylated, a sign that gene expression is completely silenced. This molecular aberration might serve as a signature that defines fragile X patients who could benefit from treatment with mGluR5 antagonists. In individuals with fragile X syndrome, the FMR1 gene can contain as many as several thousand extra repeats of the triplet base pairs CGG, a distortion that is accompanied by extra methylation at the gene’s promoter and thus impaired transcription. Because the number of triplet repeats differs widely from person to person—and even from generation to generation—there is a broad variation among patients in the structure of the gene and its methylation pattern. So when the authors tested the effects of a newly described mGluR5 inhibitor on fragile X patients, they assayed the methylation status of the FMR1 promoter, as well as running a large battery of behavioral tests designed to detect stereotypic behavior, hyperactivity, and inappropriate speech. In this clinical trial, the mGluR5 antagonist had no effect on the behaviors measured by these primary tests, but administration of the drug did correlate with differences observed in a secondary collection of tests, when the drug-treated patient group was compared with subjects who were given a placebo treatment. In a subsequent exploratory analysis, the authors found that each member of the subgroup of patients who harbored fully methylated FMR1 promoters showed improvement by the primary behavioral measures, exhibiting a boost in performance 19 or 20 days after treatment was started. The patient group with partially methylated promoters showed no such changes. This correlation between response to treatment and methylation status of the FMR1 promoter provides the basis for a larger study, appropriately designed to test whether methylation can serve as a predictor of a positive antagonist response in a population of patients with fragile X syndrome. It also offers hope that inhibition of the metabotropic glutamate system—believed to underlie many of the characteristic behaviors associated with fragile X—may be accomplished routinely, at least in patients in which the silence within lies in the FMR1 promoter. Fragile X syndrome (FXS) is an X-linked condition associated with intellectual disability and behavioral problems. It is caused by expansion of a CGG repeat in the 5′ untranslated region of the fragile X mental retardation 1 (FMR1) gene. This mutation is associated with hypermethylation at the FMR1 promoter and resultant transcriptional silencing. FMR1 silencing has many consequences, including up-regulation of metabotropic glutamate receptor 5 (mGluR5)–mediated signaling. mGluR5 receptor antagonists have shown promise in preclinical FXS models and in one small open-label study of FXS. We examined whether a receptor subtype–selective inhibitor of mGluR5, AFQ056, improves the behavioral symptoms of FXS in a randomized, double-blind, two-treatment, two-period, crossover study of 30 male FXS patients aged 18 to 35 years. We detected no significant effects of treatment on the primary outcome measure, the Aberrant Behavior Checklist–Community Edition (ABC-C) score, at day 19 or 20 of treatment. In an exploratory analysis, however, seven patients with full FMR1 promoter methylation and no detectable FMR1 messenger RNA improved, as measured with the ABC-C, significantly more after AFQ056 treatment than with placebo (P < 0.001). We detected no response in 18 patients with partial promoter methylation. Twenty-four patients experienced an adverse event, which was mostly mild to moderately severe fatigue or headache. If confirmed in larger and longer-term studies, these results suggest that blockade of the mGluR5 receptor in patients with full methylation at the FMR1 promoter may show improvement in the behavioral attributes of FXS.

Idiopathic congenital central hypoventilation syndrome: analysis of genes pertinent to early autonomic nervous system embryologic development and identification of mutations in PHOX2b.

Idiopathic congenital central hypoventilation syndrome (CCHS) has been linked to autonomic nervous system dysregulation and/or dysfunction (ANSD) since it was first described in 1970. A genetic basis of CCHS has been proposed because of the reports of four families with two affected children, because of mother–child transmission, and because of a recent report of a polyalanine expansion mutation in PHOX2b in a subset of CCHS subjects. We, therefore, studied genes pertinent to early embryologic development of the ANS including mammalian achaete‐scute homolog‐1 (MASH1), bone morphogenic protein‐2 (BMP2), engrailed‐1 (EN1), TLX3, endothelin converting enzyme‐1 (ECE1), endothelin‐1 (EDN1), PHOX2a, and PHOX2b in 67 probands with CCHS, and gender‐ and ethnicity‐matched controls. No disease‐defining mutations were identified in MASH1, BMP2, EN1, TLX3, ECE1, EDN1, or PHOX2a.The 65/67 CCHS probands (97%) were found to be heterozygous for the exon 3 polyalanine expansion mutation identified previously in PHOX2b. Further, there was an association between repeat mutation length and severity of the CCHS/ANSD phenotype. Of the two probands who did not carry the expansion mutation, one had a nonsense mutation in exon 3 which truncated the protein and the other had no mutation in PHOX2b but had a previously reported EDN3 frameshift point mutation. The polyalanine expansion mutation was not found in any of 67 matched controls. Of 54 available families (including 97 unaffected parents), whose child carried the PHOX2b mutation, 4 parents demonstrated mosaicism for an expansion mutation identical to that seen in the CCHS cases, suggesting that not all mutations in affected probands with unaffected parents are de novo. We also studied four women with CCHS who were heterozygous for the PHOX2b mutation, each with one child. Three of the four children were also affected and had the same mutation, demonstrating autosomal dominant inheritance of the mutation. Assay of the PHOX2b polyalanine repeat mutation represents a highly sensitive and specific technique for confirming the diagnosis of CCHS. Identification of the CCHS mutation will lead to clarification of the phenotype, allow for prenatal diagnosis for parents of CCHS probands and adults with CCHS in future pregnancies, and potentially direct intervention strategies for the treatment of CCHS.

An Official ATS Clinical Policy Statement: Congenital Central Hypoventilation Syndrome: Genetic Basis, Diagnosis, and Management

BACKGROUND Congenital central hypoventilation syndrome (CCHS) is characterized by alveolar hypoventilation and autonomic dysregulation. PURPOSE (1) To demonstrate the importance of PHOX2B testing in diagnosing and treating patients with CCHS, (2) to summarize recent advances in understanding how mutations in the PHOX2B gene lead to the CCHS phenotype, and (3) to provide an update on recommendations for diagnosis and treatment of patients with CCHS. METHODS Committee members were invited on the basis of their expertise in CCHS and asked to review the current state of the science by independently completing literature searches. Consensus on recommendations was reached by agreement among members of the Committee. RESULTS A review of pertinent literature allowed for the development of a document that summarizes recent advances in understanding CCHS and expert interpretation of the evidence for management of affected patients. CONCLUSIONS A PHOX2B mutation is required to confirm the diagnosis of CCHS. Knowledge of the specific PHOX2B mutation aids in anticipating the CCHS phenotype severity. Parents of patients with CCHS should be tested for PHOX2B mutations. Maintaining a high index of suspicion in cases of unexplained alveolar hypoventilation will likely identify a higher incidence of milder cases of CCHS. Recommended management options aimed toward maximizing safety and optimizing neurocognitive outcome include: (1) biannual then annual in-hospital comprehensive evaluation with (i) physiologic studies during awake and asleep states to assess ventilatory needs during varying levels of activity and concentration, in all stages of sleep, with spontaneous breathing, and with artificial ventilation, and to assess ventilatory responsiveness to physiologic challenges while awake and asleep, (ii) 72-hour Holter monitoring, (iii) echocardiogram, (iv) evaluation of ANS dysregulation across all organ systems affected by the ANS, and (v) formal neurocognitive assessment; (2) barium enema or manometry and/or full thickness rectal biopsy for patients with a history of constipation; and (3) imaging for neural crest tumors in individuals at greatest risk based on PHOX2B mutation.

Fragile X-associated tremor/ataxia syndrome: clinical features, genetics, and testing guidelines.

Fragile X‐associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder with core features of action tremor and cerebellar gait ataxia. Frequent associated findings include parkinsonism, executive function deficits and dementia, neuropathy, and dysautonomia. Magnetic Resonance Imaging studies in FXTAS demonstrate increased T2 signal intensity in the middle cerebellar peduncles (MCP sign) in the majority of patients. Similar signal alterations are seen in deep and subependymal cerebral white matter, as is general cortical and subcortical atrophy. The major neuropathological feature of FXTAS is the presence of intranuclear, neuronal, and astrocytic, inclusions in broad distribution throughout the brain and brainstem. FXTAS is caused by moderate expansions (55–200 repeats; premutation range) of a CGG trinucleotide in the fragile X mental retardation 1 (FMR1) gene, the same gene which causes fragile X syndrome when in the full mutation range (200 or greater CGG repeats). The pathogenic mechanism is related to overexpression and toxicity of the FMR1 mRNA per se. Although only recently discovered, and hence currently under‐diagnosed, FXTAS is likely to be one of the most common single‐gene disorders leading to neurodegeneration in males. In this report, we review information available on the clinical, radiological, and pathological features, and prevalence and management of FXTAS. We also provide guidelines for the practitioner to assist with identifying appropriate patients for DNA testing for FXTAS, as well as recommendations for genetic counseling once a diagnosis of FXTAS is made.

Effects of STX209 (Arbaclofen) on Neurobehavioral Function in Children and Adults with Fragile X Syndrome: A Randomized, Controlled, Phase 2 Trial

Administration of a selective GABAB agonist to individuals with fragile X syndrome improves their deficits in social avoidance, a core symptom of the disease. A Fragile Balancing Act A wide array of symptoms—including intellectual disability, anxiety, seizures, and autistic behavior—are associated with fragile X syndrome (FXS). Although some symptoms can be managed (or masked) with drugs or other therapies, treatments that target the fundamental impairments are not available. Henderson et al. and Berry-Kravis et al. now provide evidence that activation of a particular neuronal receptor can improve symptoms in both mice and humans. FXS is caused by silencing of the FMR1 gene, which encodes FMRP, an RNA binding protein that inhibits protein synthesis. In a mouse model of FXS, dendritic protein synthesis is abnormally high; FMRP is believed to regulate mRNAs important for neuronal development. Furthermore, these mice—and some humans with FXS—have an increased density of dendritic spines, which are dynamic structures that make neuronal connections. Dendritic spine plasticity is linked to learning and memory. Normally, FMRP may balance mRNA translation that is stimulated by activation of synaptic receptors that respond to glutamate, an excitatory neurotransmitter. Indeed, inhibitors of these receptors rescue many irregular phenotypes in the animal models but are not yet approved for human use. These mice also exhibit deficient signaling through a different set of receptors, which respond to the inhibitory neurotransmitter GABA—and for which clinically approved agonists already exist. Henderson et al. tested one such GABAB receptor agonist, STX209, in the mouse model and found that it decreased mRNA translation in the cortex and corrected the increased dendritic spine density. Berry-Kravis et al. studied the effects of STX209 in a double-blind, placebo-controlled crossover trial, in which 63 FXS patients received placebo or drug for 4 weeks and then switched to the other treatment. Although a measure of irritability and aggression was unchanged, social avoidance improved; the drug was well tolerated. Thus, this targeted approach, which may help restore the balance between excitatory and inhibitory neurotransmission, has promise for improving social function in FXS. Research on animal models of fragile X syndrome suggests that STX209, a γ-aminobutyric acid type B (GABAB) agonist, might improve neurobehavioral function in affected patients. We evaluated whether STX209 improves behavioral symptoms of fragile X syndrome in a randomized, double-blind, placebo-controlled crossover study in 63 subjects (55 male), ages 6 to 39 years, with a full mutation in the FMR1 gene (>200 CGG triplet repeats). We found no difference from placebo on the primary endpoint, the Aberrant Behavior Checklist—Irritability (ABC-I) subscale. In the other analyses specified in the protocol, improvement was seen on the visual analog scale ratings of parent-nominated problem behaviors, with positive trends on multiple global measures. Post hoc analysis with the ABC—Social Avoidance scale, a newly validated scale for the assessment of fragile X syndrome, showed a significant beneficial treatment effect in the full study population. A post hoc subgroup of 27 subjects with more severe social impairment showed improvements on the Vineland II–Socialization raw score, on the ABC—Social Avoidance scale, and on all global measures. STX209 was well tolerated, with 8% incidences of sedation and of headache as the most frequent side effects. In this exploratory study, STX209 did not show a benefit on irritability in fragile X syndrome. Nonetheless, our results suggest that GABAB agonists have potential to improve social function and behavior in patients with fragile X syndrome.

Abnormal elevation of FMR1 mRNA is associated with psychological symptoms in individuals with the fragile X premutation

Until recently, individuals with premutation alleles (55–200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene were believed to be psychologically unaffected. However, the recent documentation of abnormal elevation of FMR1 mRNA, discovery of fragile X‐associated tremor/ataxia syndrome (FXTAS), and reports of psychiatric disorders in children and adults with the premutation have suggested a pathogenic gene–brain–behavior mechanism. In a large collaborative study, 68 men and 144 women with the FMR1 premutation completed a psychological symptoms checklist and FMR1 genetic testing, including determination of CGG repeat size, percentage of FMR1 protein (FMRP)‐positive lymphocytes, and FMR1 mRNA levels. Relative to published norms, men and women with FXTAS symptoms reported higher levels of several types of psychological symptoms. In addition, men and women with the premutation and no overt evidence of FXTAS reported higher levels of obsessive‐compulsive symptoms. Elevated FMR1 mRNA, but not CGG repeat size or reduced FMRP (as measured by immunocytochemistry), was significantly associated with increased psychological symptoms, predominantly obsessive‐compulsive symptoms and psychoticism, in premutation men with and without FXTAS symptoms. There was no relationship between CGG repeat size, FMR1 mRNA or FMRP and psychological symptoms in premutation women unless the sample was restricted to those with skewed X‐activation ratio toward >50% active premutation alleles. The results of this study support the hypothesis that FMR1 function is associated with psychological difficulties in individuals with the premutation, and provide evidence concordant with an RNA toxic gain‐of‐function model in a neuropsychiatric phenotype.

Apolipoprotein E 4 allele, AD pathology, and the clinical expression of Alzheimer's disease

Objective: To test the hypothesis that the APOE ε4 allele is associated with the clinical manifestations of AD through an association with the pathologic hallmarks of disease. Methods: Participants were older Catholic nuns, priests, and brothers who agreed to annual neurologic and neuropsychological evaluation for AD and other common neurologic conditions and brain autopsy at the time of death. There were 77 persons without dementia and 51 with probable AD; 38 participants had one or more ε4 alleles. Results: In logistic regression analyses, controlling for age, sex, and education, the ε4 allele was strongly associated with the likelihood of clinical AD (odds = 3.46, 95% CI = 1.44 to 8.33). However, controlling for the effect of AD pathology, the association of the ε allele with clinical AD was reduced by >50% and was no longer significant (odds = 1.58, 95% CI = 0.56 to 4.43). Similarly, in linear regression analyses, controlling for age, sex, and education, the ε4 allele was strongly associated with level of cognitive function proximate to death (regression coefficient = −0.477, p = 0.005). However, after controlling for the effect of AD pathology, the association of the ε4 allele with level of cognition was reduced by >80% and was no longer significant (regression coefficient = −0.093). Similar results were found in analyses using separate measures of neuritic plaques, diffuse plaques, and neurofibrillary tangles, and in analyses of five different cognitive systems (episodic memory, semantic memory, working memory, perceptual speed, and visuospatial ability). Conclusions: The APOE ε4 allele appears to be associated with the clinical manifestations of AD through an association with the pathologic hallmarks of AD rather than another mechanism.