Updated report on tools to measure outcomes of clinical trials in fragile X syndrome

Clinical Development of Targeted Fragile X Syndrome Treatments: An Industry Perspective

Fragile X syndrome (FXS) is the leading known cause of inherited intellectual disability and autism spectrum disorder. It is caused by a mutation of the fragile X mental retardation 1 (FMR1) gene, resulting in a deficit of fragile X mental retardation protein (FMRP). The clinical presentation of FXS is variable, and is typically associated with developmental delays, intellectual disability, a wide range of behavioral issues, and certain identifying physical features. Over the past 25 years, researchers have worked to understand the complex relationship between FMRP deficiency and the symptoms of FXS and, in the process, have identified several potential targeted therapeutics, some of which have been tested in clinical trials. Whereas most of the basic research to date has been led by experts at academic institutions, the pharmaceutical industry is becoming increasingly involved with not only the scientific community, but also with patient advocacy organizations, as more promising pharmacological agents are moving into the clinical stages of development. The objective of this review is to provide an industry perspective on the ongoing development of mechanism-based treatments for FXS, including identification of challenges and recommendations for future clinical trials.

From bedside to bench and back: Translating ASD models

Autism spectrum disorders (ASD) represent a heterogeneous group of disorders defined by deficits in social interaction/communication and restricted interests, behaviors, or activities. Models of ASD, developed based on clinical data and observations, are used in basic science, the "bench," to better understand the pathophysiology of ASD and provide therapeutic options for patients in the clinic, the "bedside." Translational medicine creates a bridge between the bench and bedside that allows for clinical and basic science discoveries to challenge one another to improve the opportunities to bring novel therapies to patients. From the clinical side, biomarker work is expanding our understanding of possible mechanisms of ASD through measures of behavior, genetics, imaging modalities, and serum markers. These biomarkers could help to subclassify patients with ASD in order to better target treatments to a more homogeneous groups of patients most likely to respond to a candidate therapy. In turn, basic science has been responding to developments in clinical evaluation by improving bench models to mechanistically and phenotypically recapitulate the ASD phenotypes observed in clinic. While genetic models are identifying novel therapeutics targets at the bench, the clinical efforts are making progress by defining better outcome measures that are most representative of meaningful patient responses. In this review, we discuss some of these challenges in translational research in ASD and strategies for the bench and bedside to bridge the gap to achieve better benefits to patients.

Fragile X-Associated Disorders in Serbia: Baseline Quantitative and Qualitative Survey of Knowledge, Attitudes and Practices Among Medical Professionals

We conducted a knowledge, attitude, and practice (KAP) survey of fragile X-associated disorders (FXD) in Serbia in order to obtain baseline quantitative and qualitative KAP data on fragile X mental retardation 1 gene (FMR1) pre- and full mutations (PM, FM). The survey's 16-item questionnaire included a knowledge component (12/16), such as self-assessment knowledge (SAK) and factual knowledge (FK, 2/5 questions for PM, FXTAS and FXPOI). Education-directed attitudes in the FXD field and FMR1 DNA testing practices had 4/16 items, including brief case vignettes of FXTAS and FXPOI, respectively. The study's cohort consisted of primary care physicians (referred to as “physicians” in the rest of the text) throughout Serbia (n = 284, aged 26–64 years, 176/284, 62.2% in Belgrade, Serbia) and senior medical students (n = 245, aged 23–30 years; 33.5% males) at the Belgrade School of Medicine. Strikingly, half of the survey respondents indicated “not having any” knowledge for the fragile X gene premutation and FXD. Physicians were more likely to indicate “not having any” knowledge than students (41.2% of physicians vs. 13.1% of students, P < 0.05). Roughly half of the students had “minimal knowledge” (53.5 vs. 30.5% of physicians, P < 0.05). Low FK was common in the cohort, as few physicians had “all correct answers” (7.5 vs. 3.7% of students, P < 0.05; 16.5 vs. 9.5% of students for the 2/5 premutation-related questions). Statistical analyses identified physicians' practice setting and length of clinical experience as predictors of the lack of FK on questions related to FXD. Physicians were more likely than students to indicate “strongly agreed” to expand their knowledge of the gene premutation and FXD (90.9 vs. 66.7% of students, P < 0.01). However, students more frequently indicated that they are willing to recommend DNA testing in their future practices than physicians (93.5 vs. 64.8% of physicians, P < 0.001). In conclusion, there is a major gap in knowledge regarding fragile X gene PM and FXD among the study's participants in Serbia. The study's informative-educational survey serves as an initial step in the process of enhancing the KAP of medical professionals with regards to the fragile X gene premutation and FXD.

New Insights Into the Role of Cav2 Protein Family in Calcium Flux Deregulation in Fmr1-KO Neurons

Fragile X syndrome (FXS), the most common form of inherited intellectual disability (ID) and a leading cause of autism, results from the loss of expression of the Fmr1 gene which encodes the RNA-binding protein Fragile X Mental Retardation Protein (FMRP). Among the thousands mRNA targets of FMRP, numerous encode regulators of ion homeostasis. It has also been described that FMRP directly interacts with Ca²⁺ channels modulating their activity. Collectively these findings suggest that FMRP plays critical roles in Ca²⁺ homeostasis during nervous system development. We carried out a functional analysis of Ca²⁺ regulation using a calcium imaging approach in Fmr1-KO cultured neurons and we show that these cells display impaired steady state Ca²⁺ concentration and an altered entry of Ca²⁺ after KCl-triggered depolarization. Consistent with these data, we show that the protein product of the Cacna1a gene, the pore-forming subunit of the Ca_v2.1 channel, is less expressed at the plasma membrane of Fmr1-KO neurons compared to wild-type (WT). Thus, our findings point out the critical role that Ca_v2.1 plays in the altered Ca²⁺ flux in Fmr1-KO neurons, impacting Ca²⁺ homeostasis of these cells. Remarkably, we highlight a new phenotype of cultured Fmr1-KO neurons that can be considered a novel cellular biomarker and is amenable to small molecule screening and identification of new drugs to treat FXS.

Key issues in Rett syndrome: emotional, behavioural and autonomic dysregulation (EBAD) - a target for clinical trials

Complex neurodevelopmental disorders need multi-disciplinary treatment approaches for optimal care. The clinical effectiveness of treatments is limited in patients with rare genetic syndromes with multisystem morbidity. Emotional and behavioural dysregulation is common across many neurodevelopmental disorders. It can manifest in children across multiple diagnostic groups, including those on the autism spectrum and in rare genetic syndromes such as Rett Syndrome (RTT). There is, however a remarkable scarcity in the literature on the impact of the autonomic component on emotional and behavioural regulation in these disorders, and on the longer-term outcomes on disorder burden.RTT is a debilitating and often life-threatening disorder involving multiple overlapping physiological systems. Autonomic dysregulation otherwise known as dysautonomia is a cardinal feature of RTT characterised by an imbalance between the sympathetic and parasympathetic arms of the autonomic nervous system. Unlocking the autonomic component of emotional and behavioural dysregulation would be central in reducing the impairment seen in patients with RTT. In this vein, Emotional, Behavioural and Autonomic Dysregulation (EBAD) would be a useful construct to target for treatment which could mitigate burden and improve the quality of life of patients.RTT can be considered as a congenital dysautonomia and because EBAD can give rise to impairments occurring in multiple overlapping physiological systems, understanding these physiological responses arising out of EBAD would be a critical part to consider when planning treatment strategies and improving clinical outcomes in these patients. Biometric guided pharmacological and bio-feedback therapy for the behavioural and emotional aspects of the disorder offers an attracting perspective to manage EBAD in these patients. This can also allow for the stratification of patients into clinical trials and could ultimately help streamline the patient care pathway for optimal outcomes.The objectives of this review are to emphasise the key issues relating to the management of EBAD in patients with RTT, appraise clinical trials done in RTT from the perspective of autonomic physiology and to discuss the potential of EBAD as a target for clinical trials.

Narrative Language Sampling in Typical Development: Implications for Clinical Trials

PURPOSE

This study examined cross-sectional age-related trajectories of expressive language variables (syntactic complexity, lexical diversity, unintelligibility, dysfluency, and talkativeness) derived from a narrative language sampling procedure.

METHOD

Narrative samples were analyzed from 103 typically developing individuals, ages 4-21 years.

RESULTS

Results showed that this procedure was effective for the entire age range, with participants producing an utterance on virtually every page of the wordless picture books used to prompt the narrative. Importantly, the cross-sectional trajectories for syntactic complexity and lexical diversity showed age-related increases through the age of 18 years, although measures of other dimensions of language showed different relationships with age.

CONCLUSIONS

These data inform developmental work and document the extent to which the narrative procedure can be used to characterize expressive language over a wide age range. This procedure has been proposed as an outcome measure for clinical trials and interventions involving individuals with intellectual and developmental disabilities. The present data document the developmental levels for which the procedure and metrics derived are appropriate.

A Screening Tool to Measure Eye Contact Avoidance in Boys with Fragile X Syndrome

We examined the reliability, validity and factor structure of the Eye Contact Avoidance Scale (ECAS), a new 15-item screening tool designed to measure eye contact avoidance in individuals with fragile X syndrome (FXS). Internal consistency of the scale was acceptable to excellent and convergent validity with the Social Responsiveness Scale, Second Edition (SRS-2) and the Anxiety, Depression, and Mood Scale (ADAMS) was good. Boys with a comorbid ASD diagnosis obtained significantly higher scores on the ECAS compared to boys without ASD, when controlling for communication ability. A confirmatory factor analysis indicated that a two-factor model (avoidance and aversion) provided an excellent fit to the data. The ECAS appears to be a promising reliable and valid tool that could be employed as an outcome measure in future pharmacological/behavioral treatment trials for FXS.

Classifying and characterizing the development of adaptive behavior in a naturalistic longitudinal study of young children with autism

Background

Adaptive behavior, or the ability to function independently in ones’ environment, is a key phenotypic construct in autism spectrum disorder (ASD). Few studies of the development of adaptive behavior during preschool to school-age are available, though existing data demonstrate that the degree of ability and impairment associated with ASD, and how it manifests over time, is heterogeneous. Growth mixture models are a statistical technique that can help parse this heterogeneity in trajectories.

Methods

Data from an accelerated longitudinal natural history study (n = 105 children with ASD) were subjected to growth mixture model analysis. Children were assessed up to four times between the ages of 3 to 7.99 years.

Results

The best fitting model comprised two classes of trajectory on the Adaptive Behavior Composite score of the Vineland Adaptive Behavior Scale, Second Edition—a low and decreasing trajectory (73% of the sample) and a moderate and stable class (27%).

Conclusions

These results partially replicate the classes observed in a previous study of a similarly characterized sample, suggesting that developmental trajectory may indeed serve as a phenotype. Further, the ability to predict which trajectory a child is likely to follow will be useful in planning for clinical trials.

Electronic supplementary material

The online version of this article (10.1186/s11689-017-9222-9) contains supplementary material, which is available to authorized users.

Translating genetic and preclinical findings into autism therapies

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder characterized by social deficits and repetitive/restrictive interests. ASD is associated with multiple comorbidities, including intellectual disability, anxiety, and epilepsy. Evidence that ASD is highly heritable has spurred major efforts to unravel its genetics, revealing possible contributions from hundreds of genes through rare and common variation and through copy-number changes. In this perspective, we provide an overview of the current state of ASD genetics and of how genetic research has spurred the development of in vivo and in vitro models using animals and patient cells to evaluate the impact of genetic mutations on cellular function leading to disease. Efforts to translate these findings into successful therapies have yet to bear fruit. We discuss how the valuable insight into the disorder provided by these new models can be used to better understand ASD and develop future clinical trials.

The Search for an Effective Therapy to Treat Fragile X Syndrome: Dream or Reality?

Fragile X Syndrome (FXS) is the most common form of intellectual disability and a primary cause of autism. It originates from the lack of the Fragile X Mental Retardation Protein (FMRP), which is an RNA-binding protein encoded by the Fragile X Mental Retardation Gene 1 (FMR1) gene. Multiple roles have been attributed to this protein, ranging from RNA transport (from the nucleus to the cytoplasm, but also along neurites) to translational control of mRNAs. Over the last 20 years many studies have found a large number of FMRP mRNA targets, but it is still not clear which are those playing a critical role in the etiology of FXS. So far, no therapy for FXS has been found, making the quest for novel targets of considerable importance. Several pharmacological approaches have been attempted, but, despite some promising preclinical results, no strategy gave successful outcomes, due either to the induction of major side effects or to the lack of improvement of the phenotypes. However, these studies suggested that, in order to measure the effectiveness of a specific treatment, trials should be redesigned and new endpoints defined in FXS patients. Nevertheless, the search for new therapeutic targets for FXS is very active. In this context, the advances in animal modeling, coupled with better understanding of neurobiology and physiopathology of FXS, are of crucial importance in developing new selected treatments. Here, we discuss the pathways that were recently linked to the physiopathology of FXS (mGluR, GABAR, insulin, Insulin-like Growth Factor 1 (IGF-1), MPP-9, serotonin, oxytocin and endocannabinoid signaling) and that suggest new approaches to find an effective therapy for this disorder. Our goal with this review article is to summarize some recent relevant findings on FXS treatment strategies in order to have a clearer view of the different pathways analyzed to date emphasizing those shared with other synaptic disorders.

Fragile X syndrome

Fragile X syndrome (FXS) is the leading inherited form of intellectual disability and autism spectrum disorder, and patients can present with severe behavioural alterations, including hyperactivity, impulsivity and anxiety, in addition to poor language development and seizures. FXS is a trinucleotide repeat disorder, in which >200 repeats of the CGG motif in FMR1 leads to silencing of the gene and the consequent loss of its product, fragile X mental retardation 1 protein (FMRP). FMRP has a central role in gene expression and regulates the translation of potentially hundreds of mRNAs, many of which are involved in the development and maintenance of neuronal synaptic connections. Indeed, disturbances in neuroplasticity is a key finding in FXS animal models, and an imbalance in inhibitory and excitatory neuronal circuits is believed to underlie many of the clinical manifestations of this disorder. Our knowledge of the proteins that are regulated by FMRP is rapidly growing, and this has led to the identification of multiple targets for therapeutic intervention, some of which have already moved into clinical trials or clinical practice.

Arbaclofen in fragile X syndrome: results of phase 3 trials

Background

Arbaclofen improved multiple abnormal phenotypes in animal models of fragile X syndrome (FXS) and showed promising results in a phase 2 clinical study. The objective of the study is to determine safety and efficacy of arbaclofen for social avoidance in FXS.

Methods

Two phase 3 placebo-controlled trials were conducted, a flexible dose trial in subjects age 12–50 (209FX301, adolescent/adult study) and a fixed dose trial in subjects age 5–11 (209FX302, child study). The primary endpoint for both trials was the Social Avoidance subscale of the Aberrant Behavior Checklist-Community Edition, FXS-specific (ABC-C_FX). Secondary outcomes included other ABC-C_FX subscale scores, Clinical Global Impression-Improvement (CGI-I), Clinical Global Impression-Severity (CGI-S), and Vineland Adaptive Behavior Scales, Second Edition (Vineland-II) Socialization domain score.

Results

A total 119 of 125 randomized subjects completed the adolescent/adult study (n = 57 arbaclofen, 62 placebo) and 159/172 completed the child study (arbaclofen 5 BID n = 38; 10 BID n = 39; 10 TID n = 38; placebo n = 44). There were no serious adverse events (AEs); the most common AEs included somatic (headache, vomiting, nausea), neurobehavioral (irritability/agitation, anxiety, hyperactivity), decreased appetite, and infectious conditions, many of which were also common on placebo. In the combined studies, there were 13 discontinuations (n = 12 arbaclofen, 1 placebo) due to AEs (all neurobehavioral). The adolescent/adult study did not show benefit for arbaclofen over placebo for any measure. In the child study, the highest dose group showed benefit over placebo on the ABC-C_FX Irritability subscale (p = 0.03) and Parenting Stress Index (PSI, p = 0.03) and trends toward benefit on the ABC-C_FX Social Avoidance and Hyperactivity subscales (both p < 0.1) and CGI-I (p = 0.119). Effect size in the highest dose group was similar to effect sizes for FDA-approved serotonin reuptake inhibitors (SSRIs).

Conclusions

Arbaclofen did not meet the primary outcome of improved social avoidance in FXS in either study. Data from secondary measures in the child study suggests younger patients may derive benefit, but additional studies with a larger cohort on higher doses would be required to confirm this finding. The reported studies illustrate the challenges but represent a significant step forward in translating targeted treatments from preclinical models to clinical trials in humans with FXS.