Secretin as a Treatment for Autism: A Review of the Evidence

The Potential Role of Gut Peptide Hormones in Autism Spectrum Disorder

Gut peptide hormones are one group of secretory factors produced from gastrointestinal endocrine cells with potent functions in modulating digestive functions. In recent decades, they have been found across different brain regions, many of which are involved in autism-related social, emotional and cognitive deficits. Clinical studies have revealed possible correlation between those hormones and autism spectrum disorder pathogenesis. In animal models, gut peptide hormones modulate neurodevelopment, synaptic transmission and neural plasticity, explaining their behavioral relevance. This review article will summarize major findings from both clinical and basic research showing the role of gut peptide hormones in mediating autism-related neurological functions, and their potential implications in autism pathogenesis. The pharmaceutical value of gut hormones in alleviating autism-associated behavioral syndromes will be discussed to provide new insights for future drug development.

Use of GFCF Diets in Children with ASD. An Investigation into Parents' Beliefs Using the Theory of Planned Behaviour

Gluten free/Casein free (GFCF) diets are one of the most common types of Complementary and Alternative Medicines (CAM) used in Autism Spectrum Disorders (ASD) despite little evidence to support positive effects. There has been no theory driven literature that has investigated parent’s reasons for their use. The Theory of Planned Behaviour (TPB) was used to examine parent’s intentions to use GFCF diets for their child with an ASD. Treatment and causal beliefs were also examined. Parents (n = 33, children aged 3–17 years) were influenced by anticipated regret, positive outcomes and attitude. Future interventions should provide information to parents and health professionals about the possible causes of ASD and therapy options which are in line with current recommendations.

Systematic review of the effectiveness of pharmacological treatments for adolescents and adults with autism spectrum disorder

The variable expression of autism over the lifespan is likely to lead to different symptoms and support requirements, and to distinct responses to pharmacotherapy treatment, in older patients compared to children. This systematic review considers the effectiveness of pharmacological treatment in managing autism spectrum disorder in adolescents and adults. Following a comprehensive search of literature published in English from 1980, methodological criteria were applied to identify studies designed to reliably assess treatment effectiveness. Only five double-blind, randomized controlled trials were eligible for appraisal. All had small sample sizes (mean = 30) and brief treatment duration of no more than 12 weeks. The paucity of trials and their methodological limitations means that there is only preliminary evidence about the short-term effectiveness of a few drug treatments for this age group. There was also a lack of reliable data reported on drug safety profiles. Methodological challenges and directions for future research are discussed.

Proposed toxic and hypoxic impairment of a brainstem locus in autism

Electrophysiological findings implicate site-specific impairment of the nucleus tractus solitarius (NTS) in autism. This invites hypothetical consideration of a large role for this small brainstem structure as the basis for seemingly disjointed behavioral and somatic features of autism. The NTS is the brain's point of entry for visceral afference, its relay for vagal reflexes, and its integration center for autonomic control of circulatory, immunological, gastrointestinal, and laryngeal function. The NTS facilitates normal cerebrovascular perfusion, and is the seminal point for an ascending noradrenergic system that modulates many complex behaviors. Microvascular configuration predisposes the NTS to focal hypoxia. A subregion--the "pNTS"--permits exposure to all blood-borne neurotoxins, including those that do not readily transit the blood-brain barrier. Impairment of acetylcholinesterase (mercury and cadmium cations, nitrates/nitrites, organophosphates, monosodium glutamate), competition for hemoglobin (carbon monoxide, nitrates/nitrites), and higher blood viscosity (net systemic oxidative stress) are suggested to potentiate microcirculatory insufficiency of the NTS, and thus autism.

Global hormone profiling of murine placenta reveals Secretin expression

OBJECTIVE

To elucidate and categorize the murine placental hormones expressed across gestation, including the expression of hormones with previously undescribed roles.

STUDY DESIGN

Expression levels of all genes with known or predicted hormone activity expressed in two separate tissues, the placenta and maternal decidua, were assessed across a timecourse spanning the full lifetime of the placenta. Novel expression patterns were confirmed by in situ hybridization and protein level measurements.

RESULTS

A combination of temporal and spatial information defines five groups that can accurately predict the patterns of uncharacterized hormones. Our analysis identified Secretin, a novel placental hormone that is expressed specifically by the trophoblast at levels many times greater than in any other tissue.

CONCLUSIONS

The characteristics of Secretin fit the paradigm of known placental hormones and suggest that it may play an important role during pregnancy.

Insights into synaptic function from mouse models of human cognitive disorders

Modern approaches to the investigation of the molecular mechanisms underlying human cognitive disease often include multidisciplinary examination of animal models engineered with specific mutations that spatially and temporally restrict expression of a gene of interest. This approach not only makes possible the development of animal models that demonstrate phenotypic similarities to their respective human disorders, but has also allowed for significant progress towards understanding the processes that mediate synaptic function and memory formation in the nondiseased state. Examples of successful mouse models where genetic manipulation of the mouse resulted in recapitulation of the symptomatology of the human disorder and was used to significantly expand our understanding of the molecular mechanisms underlying normal synaptic plasticity and memory formation are discussed in this article. These studies have broadened our knowledge of several signal transduction cascades that function throughout life to mediate synaptic physiology. Defining these events is key for developing therapies to address disorders of cognitive ability.

Secretin deficiency causes impairment in survival of neural progenitor cells in mice

Hippocampal neurogenesis is the lifelong production of new neurons in the central nervous system (CNS), and affects many physiological and pathophysiological conditions, including neurobehavioral disorders. The early postnatal stage is the most prominent neurogenesis period; however, the functional role of neurogenesis in this developing stage has not been well characterized. To understand the role of hippocampal neurogenesis in the postnatal developing period, we analyzed secretin, a neuropeptide, which is expressed significantly higher in the development stage. Secretin is a pleiotropic neuropeptide hormone that belongs to the secretin/VIP/glucagon peptide family. Although secretin was originally isolated in the gastrointestinal system, it has been found that secretin itself acts as a neuropeptide in the CNS. Here, we report a new function of secretin as a survival factor for neural progenitor cells in the hippocampus. We found that secretin-deficient mice exhibit decreased numbers of BrdU-labeled new neurons and dramatically increased apoptosis of doublecortin-positive neural progenitor cells in the subgranular zone of the dentate gyrus (DG) during the early postnatal period. Furthermore, we found that reduced survival of neural progenitor cells leads to decreased volume of DG, reduced long-term potentiation and impaired spatial learning ability in adults. Our studies demonstrate that secretin has important implications for neurogenesis in postnatal development, and affects neurobehavioral function in the adult mouse.

Emerging drugs for the treatment of symptoms associated with autism spectrum disorders

IMPORTANCE OF THE FIELD

Autism spectrum disorders, or pervasive developmental disorders (PDDs), are neurodevelopmental disorders defined by qualitative impairment in social interaction, impaired communication and stereotyped patterns of behavior. The most common forms of PDD are autistic disorder (autism), Asperger's disorder and PDD not otherwise specified. Recent surveillance studies reveal an increase in the prevalence of autism and related PDDs. The use of pharmacologic agents in the treatment of these disorders can reduce the impact of interfering symptoms, providing relief for affected individuals and their families.

AREAS COVERED IN THIS REVIEW

This review examines results from neurobiologic research in an attempt to both elucidate the pathophysiology of autism and guide the development of pharmacologic agents for the treatment of associated symptoms. The safety and efficacy data of drugs currently in clinical use for the treatment of these symptoms, as well as pharmaceuticals currently under development, are discussed.

WHAT THE READER WILL GAIN

This comprehensive review will deepen the reader's current understanding of the research guiding the pharmacologic treatment of symptoms associated with autism and related PDDs. Areas of focus for future research are also discussed. The need for large-scale investigation of some commonly used pharmacologic agents, in addition to the development of drugs with improved efficacy and safety profiles, is made evident.

TAKE HOME MESSAGE

Despite progress in the development of pharmacologic treatments for a number of interfering symptom domains associated with autism and other PDDs, a great deal of work remains.

Neurofeedback for autistic spectrum disorder: a review of the literature

There is a need for effective interventions to address the core symptoms and problems associated with autistic spectrum disorder (ASD). Behavior therapy improves communication and behavioral functioning. Additional treatment options include psychopharmacological and biomedical interventions. Although these approaches help children with autistic problems, they may be associated with side effects, risks or require ongoing or long-term treatment. Neurofeedback is a noninvasive approach shown to enhance neuroregulation and metabolic function in ASD. We present a review of the literature on the application of Neurofeedback to the multiple problems associated with ASD. Directions for future research are discussed.

What's new in autism?

This review on autism spectrum disorder (ASD) focusses on recent insights in the clinical picture, such as continuity of the phenotype and the concept of broader phenotype, on epidemiology and on clinical issues relevant to physicians, including new methods for early screening and diagnosis, psychiatric and somatic co-morbidity, and the expansion of so-called complementary and alternative treatments. ASD is a disorder with mainly genetic causes and recent insights show that a variety of genetic mechanisms may be involved, i.e. single gene disorders, copy number variations and polygenic mechanisms. Technological advances in genetics have lead to a number of promising findings, which, together with other lines of fundamental research, suggest that ASD may be a disorder of connectivity in the brain, at least in a subgroup of patients. It is possible that part of the genetic load in autism actually reflects gene-environment interaction, but there is no evidence for purely environmental causes in a substantial number of cases. Clinical research suggests that ASD may be a multi-system disorder in at least a subgroup of subjects, affecting the gastro-intestinal (GI) tract, the immune system and perhaps other systems. Behavioural treatments remain the cornerstone of management, and are mainly aimed at stimulation of the domains of impaired development and reducing secondary behaviours. These treatments are constantly being refined, but the main progress in this area may be the increase of research on effectiveness.

The cyclic AMP phenotype of fragile X and autism

Cyclic AMP (cAMP) is a second messenger involved in many processes including mnemonic processing and anxiety. Memory deficits and anxiety are noted in the phenotype of fragile X (FX), the most common heritable cause of mental retardation and autism. Here we review reported observations of altered cAMP cascade function in FX and autism. Cyclic AMP is a potentially useful biochemical marker to distinguish autism comorbid with FX from autism per se and the cAMP cascade may be a viable therapeutic target for both FX and autism.

[Substitutive and dietetic approaches in childhood autistic disorder: interests and limits]

INTRODUCTION

Autism is a developmental disorder that requires specialized therapeutic approaches. Influenced by various theoretical hypotheses, therapeutic programs are typically structured on a psychodynamic, biological or educative basis. Presently, educational strategies are recommended in the treatment of autism, without excluding other approaches when they are necessary. Some authors recommend dietetic or complementary approaches to the treatment of autism, which often stimulates great interest in the parents but also provokes controversy for professionals. Nevertheless, professionals must be informed about this approach because parents are actively in demand of it.

LITERATURE FINDINGS

First of all, enzymatic disorders and metabolic errors are those most frequently evoked in the literature. The well-known phenylalanine hydroxylase deficit responsible for phenylketonuria has been described as being associated with autism. In this case, adapted diet prevents mental retardation and autistic symptoms. Some enzymatic errors are also corrected by supplementation with uridine or ribose for example, but these supplementations are the responsibility of specialized medical teams in the domain of neurology and cannot be applied by parents alone. Secondly, increased opoid activity due to an excess of peptides is also supposed to be at the origin of some autistic symptoms. Gluten-free or casein-free diets have thus been tested in controlled studies, with contradictory results. With such diets, some studies show symptom regression but others report negative side effects, essentially protein malnutrition. Methodological bias, small sample sizes, the use of various diagnostic criteria or heterogeneity of evaluation interfere with data analysis and interpretation, which prompted professionals to be cautious with such diets. The third hypothesis emphasized in the literature is the amino acid domain. Some autistic children lack some amino acids such as glutamic or aspartic acids for example and this deficiency would create autistic symptoms. However, for some authors, these deficits are attributed to nutritional deficits caused by the food selectivity of children. A fourth hypothesis concerning metabolic implication in autism is the suspicion that a food allergy phenomenon could interfere with development, and it has been observed that Ig levels are higher in autistic children than in control children. Autistic children with a positive reaction to food Ig would have a more favourable outcome with diet excluding some kinds of food; but most of those diets are drastic and ethically debatable. Fifth, glucidic catabolism could be deleterious with an excess of ketonic products that will initiate comitial seizures. Few studies with ketogenic diet have been conducted but, as it has been described with epileptic subjects, those diets would diminish autistic symptoms. Not enough studies have been conducted that would allow one to draw any firm conclusions. The sixth hypothesis is linked with vitamin deficiencies that are a notably important area of research in the treatment of autism. Vitamin B12 or B6 deficiencies have been studied in several articles, and many of them were controlled studies. French teams also emphasize an interest in supplementation with B12 or B6. The two last hypotheses concern auto-immune patterns and the toxic effects of heavy metals like mercury. There is a paucity of methodologically satisfying studies that support these two hypotheses and diet recommendations. Following these assumptions, some dietetic approaches have been recommended, even though the methodological aspects of supporting studies are poor. The most famous diet is the gluten-free and/or casein-free diet. Only two controlled studies attracted our attention. Even if for some autistic children such a diet was positive, for others, gluten-free or casein-free diets were poorly tolerated and, for some authors, not without considerable side effects, the more prejudicial of which was the Kwashiorkor risk. Ketogenic diets have been studied in one non controlled study, but even if positive results have been noted by the authors, the ketogenic diet is very restricting and the long term effects have not been evaluated. Vitamin supplementation is the one and only diet domain where there have been many repeated and placebo-controlled studies. Side effects are rare and mild even if high doses of vitamin B6 are advocated in these studies. In total, as evoked by Rimland, 11 controlled placebo-blind studies have been conducted and 50% of autistic children with this supplementation had improved autistic signs. However, these results still remain debated. Finally, more rarely, enzymatic abnormalities need specific diets which have some positive consequences, but such diets could not be applied by parents alone and are the responsibility of specialized teams. For discussion purposes we can emphasize that, in spite of the amount of studies concerning the effects of specialized diets, few are methodologically satisfying. We can not ignore that some side effects are possible with such approaches and parents need to be informed of them. Some are even potentially serious, such as diets with metal chelators. In spite of those results, vitamin supplementation seems to be the only one that some specialized teams in autism could apply, always with parent agreement. In conclusion, within this scientific field, studies on eating habits of autistic children should be conducted because of their food selectivity or avoidance.

Autism spectrum disorders in early childhood: an overview for practicing physicians

Autism spectrum disorders (ASDs) affect approximately 1 in 166 children in the United States, making it likely for the average physician to encounter patients with ASDs in his or her practice. In particular, pediatricians and developmental neurologists play a critical role in early identification, resource referrals, and management of a variety of comorbid physical and medical concerns. This article reviews the current literature on ASDs and provides recommendations for practice in areas critical to the provision of medical services.

The status of pharmacotherapy for autism spectrum disorders

The use of pharmacologic agents as a component of treatment for children and adults with autism spectrum disorders is common and a substantial body of literature describing controlled and open-label clinical trials now exists to guide clinical practice. Empiric evidence of efficacy of risperidone, methylphenidate and some selective serotonin re-uptake inhibitors for maladaptive behaviors commonly associated with autism spectrum disorders has increased substantially in recent years. Preliminary controlled trials of valproate, atomoxetine, alpha-2 adrenergic agonists and olanzapine are promising. In addition to traditional psychotropic medications, investigators have examined the potential role of a variety of agents with glutamatergic or cholinergic mechanisms, and the results warrant further investigation. Although psychotropic medications are effective in treating some important associated behaviors, evidence of significant impact on the core features of autism spectrum disorders is very limited.

How Young is Too Young for Psychotropic Medication?

Approximately 1.5% of preschool-age children receive prescribed psychiatric medications, and most of these prescriptions are written for off-label indications. These circumstances create numerous ethical issues. Few studies support the use of psychotropic medications in children younger than age 6. In addition, the effects of these medications are not fully understood in young children with rapidly maturing brains and bodies. Suggestions for nurses are offered.

Secretin receptor-deficient mice exhibit impaired synaptic plasticity and social behavior

Secretin is a peptide hormone released from the duodenum to stimulate the secretion of digestive juice by the pancreas. Secretin also functions as a neuropeptide hormone in the brain, and exogenous administration has been reported to alleviate symptoms in some patients with autism. We have generated secretin receptor-deficient mice to explore the relationship between secretin signaling in the brain and behavioral phenotypes. Secretin receptor-deficient mice are overtly normal and fertile; however, synaptic plasticity in the hippocampus is impaired and there are slightly fewer dendritic spines in the CA1 hippocampal pyramidal cells. Furthermore, secretin receptor-deficient mice show abnormal social and cognitive behaviors. These findings suggest that the secretin receptor system has an important role in the central nervous system relating to social behavior.

Novel treatments for autistic spectrum disorders

In no area of developmental pediatric practice is there more controversy regarding the choice of treatment than related to children with autistic spectrum disorders (ASD). Complementary and alternative medical therapies (CAM) are often elected because they are perceived as treating the cause of symptoms rather than the symptoms themselves. CAM used for autism can be divided by proposed mechanism: immune modulation, gastrointestinal, supplements that affect neurotransmitter function, and nonbiologic intervention. Secretin as a therapy for autism is discussed as an example of how a clinical observation rapidly grew to a widespread treatment before well-designed studies demonstrated absence of effect. The plausibility for behavioral effect was not substantiated by clinical studies. CAM used for treatment of autism is examined in terms of rationale, evidence of efficacy, side effects, and additional commentary. Families and clinicians need access to well-designed clinical evidence to assist them in choice of therapies.

The effectiveness of interventions for children with autism

Over the past 50 years very many different treatments have been promoted as bringing about significant improvements, or even cures, for children with autism. However, few interventions involve controlled studies of any kind; randomised control trials are virtually non-existent and when appropriate research methodology has been applied the results are generally far from positive. Recent research suggests that the most effective results stem from early intensive behavioural interventions. Although many questions remain concerning the optimal age at which treatment should begin, the intensity of treatment and the many other variables that may affect outcome, there is growing evidence of general strategies that can be effective in ameliorating the problems associated with autism.