Histidinemia and infantile autism

Metabolomic Signatures of Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is associated with many variations in metabolism, but the ex-act correlates of these metabolic disturbances with behavior and development and their links to other core metabolic disruptions are understudied. In this study, large-scale targeted LC-MS/MS metabolomic analysis was conducted on fasting morning plasma samples from 57 children with ASD (29 with neurodevelopmental regression, NDR) and 37 healthy controls of similar age and gender. Linear model determined the metabolic signatures of ASD with and without NDR, measures of behavior and neurodevelopment, as well as markers of oxidative stress, inflammation, redox, methylation, and mitochondrial metabolism. MetaboAnalyst ver 5.0 (the Wishart Research Group at the University of Alberta, Edmonton, Canada) identified the pathways associated with altered metabolic signatures. Differences in histidine and glutathione metabolism as well as aromatic amino acid (AAA) biosynthesis differentiated ASD from controls. NDR was associated with disruption in nicotinamide and energy metabolism. Sleep and neurodevelopment were associated with energy metabolism while neurodevelopment was also associated with purine metabolism and aminoacyl-tRNA biosynthesis. While behavior was as-sociated with some of the same pathways as neurodevelopment, it was also associated with alternations in neurotransmitter metabolism. Alterations in methylation was associated with aminoacyl-tRNA biosynthesis and branched chain amino acid (BCAA) and nicotinamide metabolism. Alterations in glutathione metabolism was associated with changes in glycine, serine and threonine, BCAA and AAA metabolism. Markers of oxidative stress and inflammation were as-sociated with energy metabolism and aminoacyl-tRNA biosynthesis. Alterations in mitochondrial metabolism was associated with alterations in energy metabolism and L-glutamine. Using behavioral and biochemical markers, this study finds convergent disturbances in specific metabolic pathways with ASD, particularly changes in energy, nicotinamide, neurotransmitters, and BCAA, as well as aminoacyl-tRNA biosynthesis.

Altered expression of histamine signaling genes in autism spectrum disorder

The histaminergic system (HS) has a critical role in cognition, sleep and other behaviors. Although not well studied in autism spectrum disorder (ASD), the HS is implicated in many neurological disorders, some of which share comorbidity with ASD, including Tourette syndrome (TS). Preliminary studies suggest that antagonism of histamine receptors 1-3 reduces symptoms and specific behaviors in ASD patients and relevant animal models. In addition, the HS mediates neuroinflammation, which may be heightened in ASD. Together, this suggests that the HS may also be altered in ASD. Using RNA sequencing (RNA-seq), we investigated genome-wide expression, as well as a focused gene set analysis of key HS genes (HDC, HNMT, HRH1, HRH2, HRH3 and HRH4) in postmortem dorsolateral prefrontal cortex (DLPFC) initially in 13 subjects with ASD and 39 matched controls. At the genome level, eight transcripts were differentially expressed (false discovery rate <0.05), six of which were small nucleolar RNAs (snoRNAs). There was no significant diagnosis effect on any of the individual HS genes but expression of the gene set of HNMT, HRH1, HRH2 and HRH3 was significantly altered. Curated HS gene sets were also significantly differentially expressed. Differential expression analysis of these gene sets in an independent RNA-seq ASD data set from DLPFC of 47 additional subjects confirmed these findings. Understanding the physiological relevance of an altered HS may suggest new therapeutic options for the treatment of ASD.

Histaminergic system in brain disorders: lessons from the translational approach and future perspectives

Histamine and its receptors were first described as part of immune and gastrointestinal systems, but their presence in the central nervous system and importance in behavior are gaining more attention. The histaminergic system modulates different processes including wakefulness, feeding, and learning and memory consolidation. Histamine receptors (H1R, H2R, H3R, and H4R) belong to the rhodopsin-like family of G protein-coupled receptors, present constitutive activity, and are subjected to inverse agonist action. The involvement of the histaminergic system in brain disorders, such as Alzheimer's disease, schizophrenia, sleep disorders, drug dependence, and Parkinson's disease, is largely studied. Data obtained from preclinical studies point antagonists of histamine receptors as promising alternatives to treat brain disorders. Thus, clinical trials are currently ongoing to assess the effects of these drugs on humans. This review summarizes the role of histaminergic system in brain disorders, as well as the effects of different histamine antagonists on animal models and humans.

B vitamin supplementation reduces excretion of urinary dicarboxylic acids in autistic children

Urinary dicarboxylic acids are an important source of information about metabolism and potential problems especially connected with energy production, intestinal dysbiosis, and nutritional individuality in autistic children. A diet rich in vitamins and macroelements is a new idea of intervention in autism. The objective of the present study was to test the hypothesis that vitamin B2, vitamin B6, and magnesium supplementation is effective in reducing the level of dicarboxylic acids in the urine of autistic children. We examined the levels of succinic, adipic, and suberic acids in the urine of autistic children before and after vitamin supplementation. Thirty children with autism received magnesium (daily dose, 200 mg), vitamin B6 (pyridoxine; daily dose, 500 mg), and vitamin B2 (riboflavin; daily dose, 20 mg). The treatment was provided for a period of 3 months. Organic acids were determined using gas chromatography/mass spectrometry. Before supplementation, the levels of succinic, adipic, and suberic acids in the urine of autistic children were 41.47 ± 50.40 μmol/mmol creatinine, 15.61 ± 15.31 μmol/mmol creatinine, 8.02 ± 6.08 μmol/mmol creatinine; and after supplementation, the levels were 9.90 ± 8.26 μmol/mmol creatinine, 2.92 ± 2.41 μmol/mmol creatinine, and 2.57 ± 3.53 μmol/mmol creatinine, respectively. The results suggest that the supplementation reduces the level of dicarboxylic acid in the urine of autistic children.

Theoretical aspects of autism: causes--a review

Autism, a member of the pervasive developmental disorders (PDDs), has been increasing dramatically since its description by Leo Kanner in 1943. First estimated to occur in 4 to 5 per 10,000 children, the incidence of autism is now 1 per 110 in the United States, and 1 per 64 in the United Kingdom, with similar incidences throughout the world. Searching information from 1943 to the present in PubMed and Ovid Medline databases, this review summarizes results that correlate the timing of changes in incidence with environmental changes. Autism could result from more than one cause, with different manifestations in different individuals that share common symptoms. Documented causes of autism include genetic mutations and/or deletions, viral infections, and encephalitis following vaccination. Therefore, autism is the result of genetic defects and/or inflammation of the brain. The inflammation could be caused by a defective placenta, immature blood-brain barrier, the immune response of the mother to infection while pregnant, a premature birth, encephalitis in the child after birth, or a toxic environment.

[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 and metabolic diseases

Autism is an etiologic heterogeneous entity caused by many different diseases occurring in the central nervous system at an early stage in life. Several metabolic defects have been associated with autistic symptoms with a rate higher than that found in the general population. Inborn errors of metabolism can probably account for less than 5% of individuals. Selective metabolic testing should be done in the presence of suggestive clinical findings, including lethargy, cyclic vomiting, early seizures, dysmorphic features, and mental retardation. In some patients, early diagnosis of the metabolic disorders and proper therapeutic interventions may significantly improve the long-term cognitive and behavioral outcome.

Autism: xenobiotic influences

The advances in medical technology during the last four decades has provided evidence for an underlying neurological basis for autism. The etiology for the variations of neurofunctional anomalies found in the autistic spectrum behaviors appears inconclusive as of this date but growing evidence supports the proposal that chronic exposure to toxic agents, i.e., xenobiotic agents, to a developing central nervous system may be the best model for defining the physiological and behavioral data found in these populations. A total of 20 subjects (15 males and 5 females) who received a formal diagnosis of autism by a developmental pediatrician, pediatric neurologist, or licensed psychologist were included. The mean age for the sample was 6.35 yrs offnge = 3-12 years). This study employed several measures that collectively would provide evidence of burden levels of xenobiotic agents and abnormal liver detoxication processes. These included: (1) Glucaric Acid Analysis, (2) blood analyses for identification of specific xenobiotic agents, and (3) Comprehensive Liver Detoxification Evaluation. Kolmogorov-Smirnov testing for a chi-square and Normal distribution of the Glucaric Acid finding indicates that each of these distributions is significantly different from expected distributions (p < .01). It is most noteworthy that of the 20 cases examined for this study, 100% of the cases showed liver detoxication profiles outside of normal. An examination of 18 autistic children in blood analyses that were available showed that 16 of these children showed evidence of levels of toxic chemicals exceeding adult maximum tolerance. In the two cases where toxic chemical levels were not found, there was abnormal D-glucaric acid findings suggesting abnormal xenobiotic influences on liver detoxication processes. A proposed mechanism for the interaction of xenobiotic toxins with immune system dysfunction and continuous and/or progressive endogenous toxicity is presented as it relates to the development of behaviors found in the autistic spectrum.

Histidinemia: a biochemical variant or a disease?

Histidemia, first described by Ghadimi in 1961, is caused by a defect in histidase. The defect results in elevated urinary excretion of histidine and its transamination products, and in high blood histidine. Blood histidine levels in histidinemic patients range from 290 to 1420 microM (normal 70-120 microM). The clinical picture of histidinemia varies from complete normality to severe retardation, with many patients being asymptomatic. No correlation has been found between clinical and biochemical data. Most reported cases have been identified in newborn screening programs. Frequency of histidinemia ranges from 1 in 8000 (Japan) to 1 in 37,000 (Sweden). Histidinemia is inherited as an autosomal recessive trait. Maternal histidinemia is believed to be benign. Studies in animal models have shown similar metabolic changes in animals and humans, but clinical changes differ. Histidinemia may be treated with a low-histidine diet, which reduces elevated histidine levels, although in most cases no improvement of clinical symptoms has been observed.

Receptor inhibition by immunoglobulins: specific inhibition by autistic children, their relatives, and control subjects

Forty-two parents of children with autistic disorder, 15 children with autistic disorder, 17 siblings of children with autistic disorder, and 12 unrelated normal adult controls were studied to determine if immunoglobulins isolated from their plasma would inhibit binding of the 5HT1A agonist, [3H]-8-hydroxy-N,N-dipropyl-2-aminotetralin (DPAT) to 5HT1A receptors in human hippocampal membranes. There were no significant differences among the means of percentage inhibition of DPAT binding of parents, children with autistic disorder, siblings, or unrelated controls. In addition, there were no differences in the proportion of subjects with > 15% DPAT inhibition among autistic children, their parents, their siblings, or unrelated controls. Immunoglobulin inhibition was not specific for the 5HT1A receptor binding site, since immunoglobulins inhibited binding to 5HT2, D1, D2, and alpha 2-adrenergic binding sites. The immunoglobulins isolated from normal controls inhibited [3H]-rauwolscine binding at alpha 2-adrenergic sites less than immunoglobulins of children with autistic disorder and their parents and siblings. This study did not support the hypothesis that autoantibodies to 5HT1A or 5HT2 receptors are characteristic of autistic disorder.

The neurobiology and genetics of infantile autism

Autism is a syndrome with multiple etiologies, as is made clear both by the evidence of neurobiological research and by the catalog of disorders that present with autistic behaviors. What remains unclear are the specific neuropathological mechanisms that produce autistic behaviors; for example, is there a common neuroanatomic pathology for all cases of autism, or can autistic behaviors emerge from different pathological sequences within the brain? Although it is premature to generalize, neuropathological studies appear to have identified common abnormalities in the cerebellum and limbic system of at least five autistic subjects. These subjects, with variable levels of mental retardation, demonstrated marked Purkinje cell loss in the cerebellar hemispheres, together with retained fetal neuronal circuitry in cerebellar nuclei and increased neuronal packing in specific regions of the limbic system, amygdala, and hippocampus. The architecture of the cerebral cortex was not affected. Although our knowledge of brain functioning is incomplete, alterations of the kind noted in the cerebellum and limbic system could reasonably produce autistic behaviors. For more detail, readers are directed to a review of cerebellar contributions to higher functions by Schmahmann (1991). Neuroimaging studies allow less resolution of brain structure than do neuroanatomic studies, and the reported findings from neuroimaging are somewhat contradictory. However, a number of investigators have reported structural abnormalities in ventricle size and cerebral hemispheric asymmetry using CT. MRI, which offers greater resolution, has uncovered some consistent findings, along with a variety of nonspecific abnormalities. Common abnormalities include reduced volume of cerebellar hemispheres and vermal lobules--findings not inconsistent with the above-mentioned neuropathological defects. It is also interesting to note that individuals with fragile X syndrome have similar cerebellar findings. PET and NMR studies of autism are at a preliminary stage, but these methodologies allow insight into the functioning of the brain, rather than simply brain anatomy. Recent PET studies indicating decreased association between paired regions of the brains of autistic subjects are of interest, particularly if they can be confirmed and refined by additional studies. Neurophysiological studies also offer insight into brain function, but are subject to numerous methodological criticisms. Nevertheless, recent reports of diminished P300 waves and absent NC components in autistic subjects seem to indicate fundamental defects in attention and secondary processing, which could help explain the self-stimulatory behaviors often seen in autism. The disturbances in brain development associated with autism can be produced in a number of ways, and at different times during development of the nervous system.(ABSTRACT TRUNCATED AT 400 WORDS)

Autism: familial aggregation and genetic implications

A review of the current literature suggests that genetic factors play an important role in the etiology of autism. It is likely that the etiology of currently idiopathic cases of autism will be shown to be heterogeneous, just as the few known etiologies are both environmental and genetic. Moreover, we would speculate that within the group of cases shown to have genetic etiologies, more than one genetic locus will be found. Some evidence suggests that quite often it is not autism itself that is inherited but rather some genetic abnormality of language or sociability that interacts with other factors to produce autism.

The functional neuroanatomy of infantile autism

Infantile autism is a behavioral syndrome consisting of specific disturbances of social relating and communication, language, response to objects, sensory sensitivity and motility. The uniqueness of this syndrome suggests one underlying pathophysiologic mechanism, although multiple etiologies, which could activate or replicate such a mechanism, have been demonstrated. Review of considerable experimental evidence and clinical observation suggests that the symptomatology of autism, including the disturbances of social relating and communication, can best be explained as a disorder of sensory modulation. This in turn suggests a neurophysiologic mechanism consisting of dysfunction of a cascading series of neurophysiologic levels or interacting neuronal loops in the brainstem and diencephalon which subserve modulation of sensory input. Some of those same systems modulate motor output in response to sensory input, and their dysfunction may release the abnormal perseverative motility of infantile autism. Other experimental evidence and clinical observations stress the language deficits of autism and implicate dysfunction of cortical structures. Brainstem and diencephalic centers project rostrally to telencephalic structures and these, in turn, modify brainstem and diencephalic function. Theories of rostrally and caudally directed sequences of pathoneurophysiologic contributions to the system dysfunction in autism are compared. It is concluded that the symptoms of autism can best be explained in terms of dysfunction of brainstem and related diencephalic behavioral systems and their elaboration and refinement by selected higher neural structures.