Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0004352 (autism)
 32,579 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The well-replicated platelet hyperserotonemia of autism has stimulated interest in serotonin (5-HT) in autism. We have examined the effects of the serotonin transporter gene (5-HTT, locus SLC6A4) promoter polymorphism (5-HTTLPR) on platelet 5-HT physiology in autism. Platelet 5-HT uptake rates and affinities (V(max) and K(m)), uptake site densities (B(max)) and 5-HT levels were examined in 31 French individuals with autism genotyped with respect to the 5-HTTLPR. Platelet 5-HT uptake and 5-HT levels were measured using HPLC; uptake sites were determined by radioligand binding. A 1.5-fold increased rate (V(max)) of platelet 5-HT uptake was observed in ll genotype individuals compared to those with ls and ss genotypes (Mann- Whitney U-test, P = 0.022). However, no significant relationship was observed between genotype and uptake site density (U-test, P = 0.51). Although median levels of platelet 5-HT in platelet-rich plasma were higher in the ll group, only trend level significance was observed (U-test, P= 0.069); platelet 5-HT content measured in whole blood was similar across genotypes. Uptake rates were well correlated with B(max) values (r = 0.66, P = 0.002); correlations between uptake and platelet 5-HT levels and between B(max) values and 5-HT levels were somewhat lower. While 5-HTTLPR alleles had an appreciable effect on platelet 5-HT uptake rates, effects on 5-HT levels and uptake site density were smaller or absent. Based on these preliminary data and prior studies of allele frequencies, we conclude that the 5-HTTLPR is not a major determinant of the group mean platelet serotonin elevation seen in autism. However, a role for increased uptake in the hyperserotonemia of autism can not be ruled out. In addition, it appears that studies of platelet 5-HT measures in autism and other disorders should take account of the effects of 5-HTTLPR genotype on 5-HT uptake
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PMID:Serotonin transporter promoter variants in autism: functional effects and relationship to platelet hyperserotonemia. 1223 75

Recently, the addition of drugs with prominent 5-HT(2) receptor antagonist properties (risperidone, olanzapine, mirtazapine, and mianserin) to selective serotonin reuptake inhibitors (SSRIs) has been shown to enhance therapeutic responses in patients with major depression and treatment-refractory obsessive-compulsive disorder (OCD). These 5-HT(2) antagonists may also be effective in ameliorating some symptoms associated with autism and other pervasive developmental disorders (PDDs). At the doses used, these drugs would be expected to saturate 5-HT(2A) receptors. These findings suggest that the simultaneous blockade of 5-HT(2A) receptors and activation of an unknown constellation of other 5-HT receptors indirectly as a result of 5-HT uptake inhibition might have greater therapeutic efficacy than either action alone. Animal studies have suggested that activation of 5-HT(1A) and 5-HT(2C) receptors may counteract the effects of activating 5-HT(2A) receptors. Additional 5-HT receptors, such as the 5-HT(1B/1D/5/7) receptors, may similarly counteract the effects of 5-HT(2A) receptor activation. These clinical and preclinical observations suggest that the combination of highly selective 5-HT(2A) antagonists and SSRIs, as well as strategies to combine high-potency 5-HT(2A) receptor and 5-HT transporter blockade in a single compound, offer the potential for therapeutic advances in a number of neuropsychiatric disorders.
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PMID:Synergistic action of 5-HT2A antagonists and selective serotonin reuptake inhibitors in neuropsychiatric disorders. 1258 95

There are cumulative data indicating involvement of the 5-HT system in autistic disorder. Most studies examining 5-HT function have focused on whole blood 5-HT content. The carbohydrate-rich meal test (CRMT) is a dietary manipulation that could significantly influence platelet-poor plasma (PPP) 5-HT levels and reflect the responsiveness of the serotonergic system in 'free' plasma. In this study, CRMT was used as an indicator of 5-HT responsivity in drug-free adults with autistic disorder (n = 7), compared with normal controls (n = 10). The PPP 5-HT levels were measured at baseline and during 3 h after administration of the CRMT. A significant elevation in PPP 5-HT levels in adult autistic patients was reached 60 min after meal administration (p < 0.03 vs control and p = 0.05 vs baseline) and a significant decrease was noted after 120 min (p < 0.01 vs baseline). In contrast to the biphasic response of the autistic patients, normal controls exhibited a gradual linear increase of PPP 5-HT levels. Our results indicate that in adult autistic patients, the pattern of PPP 5-HT responsivity to a dietary challenge of CRMT is dysregulated compared with normal controls and provide further support for the role of 5-HT in autism.
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PMID:The platelet-poor plasma 5-HT response to carbohydrate rich meal administration in adult autistic patients compared with normal controls. 1285 28

The Smith-Lemli-Opitz syndrome (SLOS) is a malformation/mental retardation syndrome resulting from an inborn error in 3beta-hydroxysteroid Delta7-reductase (DHCR7), the terminal enzyme required for cholesterol biosynthesis. Using a targeting strategy designed to virtually eliminate Dhcr7 activity, we have created a SLOS mouse model that exhibits commissural deficiencies, hippocampal abnormalities, and hypermorphic development of serotonin (5-HT) neurons. The latter is of particular interest with respect to current evidence that serotonin plays a significant role in autism spectrum disorders and the recent clinical observation that 50% of SLOS patients present with autistic behavior. Immunohistochemical analyses have revealed a 306% increase in the area of 5-HT immunoreactivity (5-HT IR) in the hindbrains of mutant (Dhcr7-/-) mice as compared to age-matched wild type animals. Amount of 5-HT IR was measured as total area of IR per histological section. Additionally, a regional increase as high as 15-fold was observed for the most lateral sagittal hindbrain sections. In Dhcr7-/- mice, an expansion of 5-HT IR into the ventricular zone and floor plate region was observed. In addition, the rostral and caudal raphe groups exhibited a radial expansion in Dhcr7-/- mice, with 5-HT IR cells present in locations not seen in wild type mice. This increase in 5-HT IR appears to represent an increase in total number of 5-HT neurons and fibers. These observations may help explain the behavioral phenotype seen in SLOS, and provide clues for future therapeutic interventions that utilize pharmacological modulation of the serotonergic system.
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PMID:Abnormal serotonergic development in a mouse model for the Smith-Lemli-Opitz syndrome: implications for autism. 1465 96

The role of the serotonin system in the etiology and pathogenesis of autism spectrum disorders (ASD) is not clearly defined. High levels of platelet serotonin (5-HT) have been consistently found in a proportion of patients, and it is known that specific 5-HT transporter gene (SLC6A4) variants modulate transporter reuptake function, therefore possibly influencing the occurrence of hyperserotonemia in a subset of autistic patients. We have examined the association of platelet serotonin levels with two SLC6A4 polymorphisms, 5-HTT gene-linked polymorphic region (HTTLPR) in the promoter and intron 2 variable number of tandem repeats (VNTR), in a sample of 105 ASD patients, their parents, and 52 control children. Quantitative transmission disequilibrium test (QTDT) results showed a significant effect on 5-HT levels of each SLC6A4 marker (P=0.017 for HTTLPR; P=0.047 for intron 2 VNTR) and of haplotypes of the two markers (P=0.017), with a major contribution of the L.Stin2.10 haplotype (P=0.0013). A 5-HT mean value in the range of hyperserotonemia was associated with the homozygous L.Stin2.10 haplotype (H (1,N=97)=7.76, P=0.0054), which occurred in 33% of hyperserotonemic patients against 6% of patients with normal 5-HT levels (Fisher's exact test: P=0.013, OR=8). Allele interaction at the HTTLPR locus was found, with a significant dominance variance effect on 5-HT levels. We found no transmission disequilibrium of any of the SLC6A4 variants in ASD. Our results show that the SLC6A4 gene is a significant factor in the determination of 5-HT levels, and that specific SLC6A4 variants are associated with an increased risk for hyperserotonemia in our sample of autistic patients. The biological mechanism, however, is unlikely to involve the SLC6A4 gene solely. The associated SLC6A4 alleles likely interact with other genes or environmental factors to produce the abnormally high 5-HT levels observed in this subset of autistic patients, who possibly represent a separate etiological group.
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PMID:Variants of the serotonin transporter gene (SLC6A4) significantly contribute to hyperserotonemia in autism. 1509 87

Autism is a neurodevelopmental disorder characterized by dysfunction in three primary behavioural domains: repetitive behaviours, social deficits, and language abnormalities. There is evidence that abnormalities exist in the serotonin (5-HT) system in autism spectrum patients. Furthermore, 5-HT is known to play a role in repetitive and social behaviours. This study examined the effect of m-chlorophenylpiperazine (m-CPP) on repetitive behaviours and prolactin response in 11 adults with autism or Aspergers disorder and 8 age- and gender-matched healthy controls via randomized double-blind, m-CPP and placebo challenges. The primary outcome measure was an instrument rating six repetitive behaviours: need to know, repeating, ordering, need to tell/ask, self-injury, and touching. Patients with autism spectrum disorders showed a significant increase in repetitive behaviours at end-point following oral m-CPP in comparison to placebo. Additionally subjects with autism spectrum disorders showed a significantly increased prolactin response to m-CPP compared to normal controls, with neither group responding to placebo. This study provides further evidence for altered 5-HT sensitivity in individuals with autism spectrum disorders, as well as a possible relationship between repetitive behaviours in autism spectrum disorders and abnormalities in the 5-HT system.
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PMID:Increased repetitive behaviours and prolactin responsivity to oral m-chlorophenylpiperazine in adults with autism spectrum disorders. 1513 62

The biological causes of autism are unknown. Since the early 1960s, the most consistent pathophysiological finding in autistic individuals has been their statistically elevated blood 5-hydroxytryptamine (5-HT, serotonin) levels. However, many autistic individuals have normal blood 5-HT levels, so this finding has been difficult to interpret. The serotonin transporter (SERT) controls 5-HT uptake by blood platelets and has been implicated in autism, but recent studies have found no correlation between SERT polymorphisms and autism. Finally, autism is considered a brain disorder, but studies have so far failed to find consistent serotonergic abnormalities in autistic brains. A simple mathematical model may account for these paradoxes, if one assumes that autism is associated with the failure of a molecular mechanism that both regulates 5-HT release from gut enterochromaffin cells and mediates 5-HT signaling in the brain. Some 5-HT receptors may play such a dual role. While the failure of such a mechanism may lead to consistent abnormalities of synaptic transmission with no alteration of brain 5-HT levels, its effects on blood 5-HT levels may appear paradoxical.
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PMID:Serotonergic paradoxes of autism replicated in a simple mathematical model. 1569 91

We report a possible association between autism in our sample and a recently described brain-expressed tryptophan hydroxylase gene (TPH2). The well-replicated involvement of the serotonin neurotransmitter system in autism has stimulated interest in many genes in the serotonin pathway as possible candidates for mutations leading to autism susceptibility. Serotonin synthesis is controlled by the rate-limiting enzyme tryptophan hydroxylase. A mouse study of the original tryptophan hydroxylase gene (TPH1) and the new isoform (TPH2) showed that while TPH1 is primarily expressed peripherally, TPH2 is found exclusively in brain tissue. We searched for human sequence variants in 6,467 nucleotides covering all 11 exons of TPH2, and also 248 nucleotides upstream of the start codon, and 935 nucleotides downstream of the stop codon. Eighteen variants were characterized in 88 subjects with autism studied at our two centers, and 95 unrelated control subjects. Using a model-free association method and empirical P value estimation, two variants showed frequency differences between autism and control subjects (P = 0.01 for a T-G variant in intron 1, and P = 0.02 for a A-T variant in intron 4). A haplotype including these variants showed slightly increased significance (P = 0.005). Further investigation of clinical phenotypes showed a possible association between presence of the variants at these two SNPs and higher scores on the Autism Diagnostic Interview (ADI) domain describing repetitive and stereotyped behaviors (P = 0.007). We conclude that TPH2 may play a modest role in autism susceptibility, perhaps relating specifically to repetitive behaviors, pending replication of this result.
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PMID:Possible association between autism and variants in the brain-expressed tryptophan hydroxylase gene (TPH2). 1576 92

Serotonin (5-hydroxytryptamine, 5-HT) is an amine neurotransmitter derived from tryptophan and is important in brain systems regulating mood, emotional behavior, and sleep. Selective serotonin reuptake inhibitor (SSRI) drugs are used to treat disorders such as depression, stress, eating disorders, autism, and schizophrenia. It is thought that these drugs act to prolong the action of 5-HT by blocking reuptake. This may lead to decreased 5-HT content in the nerve fibers themselves; however, this has not previously been directly demonstrated. We have studied the effects of administration of two drugs, imipramine and citalopram, on levels of 5-HT in nerve fibers in the murine brain. Quantitative analysis of the areal density of 5-HT fibers throughout the brain was performed using ImageJ software. While a high density of fibers was observed in mid- and hind-brain regions and areas such as thalamus and hypothalamus, densities were far lower in areas such as cortex, where SSRIs might be thought to exert their actions. As anticipated, imipramine and citalopram produced a decline in 5-HT levels in nerve fibers, but the result was not uniform. Areas such as inferior colliculus showed significant reduction whereas little, if any, change was observed in the adjacent superior colliculus. The reason for, and significance of, this regionality is unclear. It has been proposed that serotonin effects in the brain might be linked to changes in glutamatergic transmission. Extracellular glutamate levels are regulated primarily by glial glutamate transporters. Qualitative evaluation of glutamate transporter immunolabeling in cortex of control and drug-treated mice revealed no discernable difference in intensity of glutamate transporter immunoreactivity. These data suggest that changes in intracellular and extracellular levels of serotonin do not cause concomitant changes in astroglial glutamate transporter expression, and thus cannot represent a mechanism for the delayed efficacy of antidepressants when administered clinically.
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PMID:Quantitative analysis of immunolabeling for serotonin and for glutamate transporters after administration of imipramine and citalopram. 1585 94

Serotonin regulates several aspects of brain development, and it is involved in a range of behaviors frequently disturbed in autistic disorder. The serotonin transporter is a critical component of the serotonergic system. The serotonin transporter gene (SLC6A4) is of special interest given the nature of the biological findings and the reported effects of selective serotonin reuptake inhibitors of autistic symptoms. So far the genetics researches of the SLC6A4 gene have given conflicting results. The aim of study was to investigate the association between the SLC6A4 gene and autism in the Chinese Han population. The present study was conducted with the detection of three single nucleotide polymorphisms (SNP(S)) located within the SLC6A4 gene by using the polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) analysis. We performed a family-based association study of these polymorphisms in 175 Chinese Han family trios. Linkage disequilibrium (LD) measurement (D') analysis showed the presence of LD between markers across the locus. No significant evidence of association was found at any of the markers detected by using the transmission disequilibrium test (TDT) and haplotype analyses in all samples and male samples. Our findings suggest that it is unlikely that DNA variations in the SLC6A4 gene play a significant role in the genetic predisposition to autism in the Chinese Han population or that allelic heterogeneity at the SLC6A4 loci dilutes potential disease-allele association.
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PMID:Lack of evidence for association between the serotonin transporter gene (SLC6A4) polymorphisms and autism in the Chinese trios. 1588 79


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