Fenfluramine response in high and low functioning autistic children

Fenfluramine repurposing from weight loss to epilepsy: What we do and do not know

In 2020, racemic-fenfluramine was approved in the U.S. and Europe for the treatment of seizures associated with Dravet syndrome, through a restricted/controlled access program aimed at minimizing safety risks. Fenfluramine had been used extensively in the past as an appetite suppressant, but it was withdrawn from the market in 1997 when it was found to cause cardiac valvulopathy. Available evidence indicates that appetite suppression and cardiac valvulopathy are mediated by different serotonergic mechanisms. In particular, appetite suppression can be ascribed mainly to the enantiomers d-fenfluramine and d-norfenfluramine, the primary metabolite of d-fenfluramine, whereas cardiac valvulopathy can be ascribed mainly to d-norfenfluramine. Because of early observations of markedly improved seizure control in some forms of epilepsy, fenfluramine remained available in Belgium through a Royal Decree after 1997 for use in a clinical trial in patients with Dravet syndrome at average dosages lower than those generally prescribed for appetite suppression. More recently, double-blind placebo-controlled trials established its efficacy in the treatment of convulsive seizures associated with Dravet syndrome and of drop seizures associated with Lennox-Gastaut syndrome, at doses up to 0.7 mg/kg/day (maximum 26 mg/day). Although no cardiovascular toxicity has been associated with the use of fenfluramine in epilepsy, the number of patients exposed to date has been limited and only few patients had duration of exposure longer than 3 years. This article analyzes available evidence on the mechanisms involved in fenfluramine-induced appetite suppression, antiseizure effects and cardiovascular toxicity. Despite evidence that stimulation of 5-HT_2B receptors (the main mechanism leading to cardiac valvulopathy) is not required for antiseizure activity, there are many critical gaps in understanding fenfluramine's properties which are relevant to its use in epilepsy. Particular emphasis is placed on the remarkable lack of publicly accessible information about the comparative activity of the individual enantiomers of fenfluramine and norfenfluramine in experimental models of seizures and epilepsy, and on receptors systems considered to be involved in antiseizure effects. Preliminary data suggest that l-fenfluramine retains prominent antiseizure effects in a genetic zebrafish model of Dravet syndrome. If these findings are confirmed and extended to other seizure/epilepsy models, there would be an incentive for a chiral switch from racemic-fenfluramine to l-fenfluramine, which could minimize the risk of cardiovascular toxicity and reduce the incidence of adverse effects such as loss of appetite and weight loss.

Studying the neurobiology of human social interaction: Making the case for ecological validity

With this commentary we make the case for an increased focus on the ecological validity of the measures used to assess aspects of human social functioning. Impairments in social functioning are seen in many types of psychopathology, negatively affecting the lives of psychiatric patients and those around them. Yet the neurobiology underlying abnormal social interaction remains unclear. As an example of human social neuroscience research with relevance to biological psychiatry and clinical psychopharmacology, this commentary discusses published experimental studies involving manipulation of the human brain serotonin system that included assessments of social behavior. To date, these studies have mostly been laboratory-based and included computer tasks, observations by others, or single-administration self-report measures. Most laboratory measures used so far inform about the role of serotonin in aspects of social interaction, but the relevance for real-life interaction is often unclear. Few studies have used naturalistic assessments in real life. We suggest several laboratory methods with high ecological validity as well as ecological momentary assessment, which involves intensive repeated measures in naturalistic settings. In sum, this commentary intends to stimulate experimental research on the neurobiology of human social interaction as it occurs in real life.

The autistic spectrum: subgroups, boundaries, and treatment

There is consensus about the disorders that comprise the autistic spectrum, with autistic disorder, Asperger's disorder, and PDD-NOS as the most typical examples and Rett's disorder and disintegrative disorder as the other components. Important controversies regarding the precise definitions of autistic spectrum disorders and the boundaries between the milder manifestations of those disorders, particularly PDD-NOS, and non-autistic conditions have not been and cannot be resolved fully as long as there is no known biologic cause or consistent biologic or psychological marker. This includes issues as basic as whether the autistic spectrum is a predominantly unitary entity or a collection of more or less similar phenotypes with multiple, varying etiologies. This is why the highest long-term priority in the area of definite diagnosis is the search for biologic marker(s) for autism and related autism spectrum disorders [91]. In the absence of a medical test to unequivocally diagnose autism, definitions of autism and related conditions are based only on manifestations in overt behavior, with all the unreliability this entails. In the future, the discovery of biologic correlates, causes, and pathogenetic pathways will undoubtedly change the way in which autism is diagnosed and lead to a new nosology [95]. Until that time the definitions in the current versions of the classification systems should be considered in a state of evolution. The key problem of the current classification systems is the fact that the boundaries between the various disorders are fuzzy. Instead of a categorical approach, a more useful description might be that of "autistic spectrum disorder," which reflects the range of severity of symptoms. Such a dimensional understanding of PDD is useful to clinicians, who may otherwise use nonspecific terms to avoid the categorical diagnosis of autism [31]. Rutter and Schopler [96] argued for separate clinical and research schemes because clinical and research needs are different. For research purposes it is desirable to have as much direct comparability across studies as possible. The focus is on a high degree of homogeneity within diagnostic groupings. A price must be paid for this detailed specification, and the main cost lies in the proportion of cases left undiagnosed. For example, there may be good scientific reasons for a narrowly defined categorical diagnosis that includes only individuals who definitely and clearly have a specifically defined condition and excludes individuals who may have the condition. For clinicians and educators, classification helps guide the selection of treatments for an individual. From this point of view, broader diagnostic concepts may be most appropriate [95].

Empirically derived subtypes of pervasive developmental disorders: a cluster analytic study

A cluster analytic study was conducted to empirically derive behaviorally homogeneous subtypes of pervasive developmental disorders (PDD). Subjects were clustered based on a broad range of behavioral symptoms which characterize autism. Behavioral variables were measured using several of the standardized psychometric instruments most commonly employed in assessing autistic individuals. The cluster solution indicated the presence of four distinct groups. Validity checks generally confirmed significant between-group differences on independent measures of social, language, and stereotyped behaviors. In addition, the four-group cluster solution was compared to previously developed typological systems of PDD (i.e., subcategories based on IQ early onset, styles of social interaction, and DSM-III-R diagnosis). Results generally supported both the behavioral homogeneity of the four subgroups and also several important between-group differences. The potential utility of using cluster analyses to explore subtypes of PDD is discussed.

Autism and pervasive developmental disorders

Autism and pervasive developmental disorder, not otherwise specified represent a complex developmental disability in which clinical signs include language delay, social unrelatedness, and unusual or restricted interests. Gradually a better understanding of these disorders as being neurologically-based developmental disorders with multiple etiologies has replaced the idea of emotional disturbance. Although pervasive developmental disorders are rare, the potentially devastating effects make early recognition by pediatricians imperative. Yet, despite promising treatment advances in education, communication technology, behavior treatments, and pharmacology, the prognosis for these disorders remains guarded.

A novel biochemical model linking dysfunctions in brain melatonin, proopiomelanocortin peptides, and serotonin in autism

A novel biochemical model for autism is presented, which proposes that a subgroup of autistic individuals may have a hypersecretion of pineal melatonin that produces a cascade of biochemical effects including a corresponding hyposecretion of pituitary proopiomelanocortin (POMC) peptides and a hypersecretion of hypothalamic opioid peptides and serotonin (5-HT). The model is reviewed, and supporting animal and clinical research, is summarized. The first arm of the model suggests that increases in pineal melatonin results in hypersecretion of 5-HT in hypothalamus and blood. The second arm of the model indicates that hypersecretion of melatonin also inhibits the release of hypothalamic corticotrophin-releasing hormone (CRH). Hyposecretion of CRH may result in decreased release of both pituitary B-endorphin (B-E) and adrenocorticotrophin hormone (ACTH); this, in turn, may result in decreased plasma concentrations of B-E, ACTH, and cortisol. In autism, a genetically determined hypersecretion of hypothalamic B-E may further contribute to an inhibition of pituitary B-E because of negative feedback inhibition. Therefore, autism may reflect a dysfunction in the pineal-hypothalamic-pituitary-adrenal axis which, modulates POMC and 5-HT systems of the brain. This model is consistent with numerous clinical investigations implicating hypersecretion of brain 5-HT and opioid peptides in autism. The model may have heuristic importance in guiding future research in the biochemistry of autism.

A possible role of proopiomelanocortin peptides in self-injurious behavior

1. The hypothesis that opioids may be involved in self-injurious behavior is supported by fifteen years of basic animal research suggesting that opioid peptides of the brain and spinal cord participate in the modulation of antinociception in animals, and research of animal models for self-injurious behavior utilizing exogenously administered opiate agonists. 2. Clinical biochemical and pharmacological research conducted over the past five years has also suggested the possibility that opioid peptides may play an important etiological role in the elaboration of self-injurious behavior in some individuals. 3. An opioid overactivity self-injurious hypothesis is supported by results of one study indicating elevated Fraction II opioids (enkephalins) in the lumbar-thecal cerebrospinal fluid of self-injurious children compared to controls, and by the five out of six published studies demonstrating statistically significant decreases in the frequency of self-injurious behavior with the opiate antagonist, naltrexone. 4. A very recent investigation has suggested that some self-injurious individuals show abnormalities in their plasma proopiomelanocortin peptide response to naltrexone, thereby indicating a possible dysfunction in the responsitivity of the proopiomelanocortin system of the hypothalamic-pituitary-adrenal axis of these individuals. 5. These data and results of other investigations have resulted in the elaboration of the original opioid hypothesis to a more comprehensive biochemical model that focuses on this proopiomelanocortin dysregulation. 6. Because of biochemical and functional interrelationships between proopiomelanocortin peptides and certain other neurochemical systems in the brain, it is proposed that pineal melatonin and serotonin may also be involved in this dysregulation. Further basic and clinical research will be needed to test the proposed biochemical model for self-injurious behavior.

A two-year follow-up of autistic children treated with fenfluramine

Six children with autism, who were treated with fenfluramine as part of a multi-center double-blind placebo-controlled crossover design study, were continued on an open trial of this medication. Follow-up evaluation of these children after 27 months indicated that numerous problems arose in the management of these children, most often resulting in discontinuation of the medication. Particularly noted were development of tolerance, appetite and weight problems, and requirements for other kinds of interventions including introduction of other psychotropic medications and change in custodial circumstances.

The effects of fenfluramine (hydrochloride) on the behaviors of fifteen autistic children

Fifteen autistic individuals were involved in an investigation using fenfluramine and placebo in a double-blind crossover design. Subjects were assessed using IQ tests, the Real Life Rating Scale (RLRS), the Adaptive Behavior Scale-School Edition (ABS-SE), and videotaped play data on 8 of 12 visits, including 2 follow-up visits. Serotonin level in platelet-poor plasma was assessed on all 12 visits. Serotonin levels decreased with the administration of fenfluramine, and increased with the reinstatement of placebo. Statistical tests revealed no significant differences on the IQ scores, the RLRS, or the ABS-SE for the drug versus the placebo conditions. Videotaped data favored the subjects while on placebo. Group and individual data were analyzed over time and indicated no significant improvements due to the drug. The implications of this research make it difficult to recommend fenfluramine as a treatment for autism.