Erik J. Mulder

Platelet Serotonin Levels in Pervasive Developmental Disorders and Mental Retardation: Diagnostic Group Differences, Within-Group Distribution, and Behavioral Correlates

OBJECTIVE To investigate group differences, the within-group distributions, and the clinical correlates of platelet serotonin (5-HT) levels in pervasive developmental disorders (PDD). METHOD Platelet 5-HT levels were measured in Dutch children and young adults, recruited from 2001 through 2003, with PDD (autism, Aspergers, and PDD-not otherwise specified [PDD-NOS]; n = 81) or with mental retardation (MR; n = 54) but without PDD, and in normal controls (n = 60). The distribution of platelet 5-HT levels was assessed using mixture-modeling analyses. Relationships between platelet 5-HT levels and a full range of demographic, clinical, and behavioral variables were examined. RESULTS Group mean (+/- SD) platelet 5-HT levels (nmol/10 platelets) were significantly higher in the autistic (4.51 +/- 1.61, n = 33) and PDD-NOS (4.90 +/- 1.54, n = 43) groups compared to the MR (3.48 +/- 1.33, n = 54) or the normal control (3.58 +/- 1.08, n = 60) groups (F4,190 = 9.35, p <.001). Platelet 5-HT values in the combined PDD group showed a bimodal distribution, and an empirical cutpoint for hyperserotonemia was determined. None of the behavioral variables examined was significantly associated with platelet 5-HT levels. CONCLUSIONS The platelet hyperserotonemia of autism was replicated in Dutch subjects. Platelet 5-HT levels were also increased in PDD-NOS, while no elevation was seen in MR. Platelet 5-HT levels appeared to be bimodally distributed in the PDD group, with an apparent hyperserotonemic subgroup.

High-density SNP association study and copy number variation analysis of the AUTS1 and AUTS5 loci implicate the IMMP2L-DOCK4 gene region in autism susceptibility.

Autism spectrum disorders are a group of highly heritable neurodevelopmental disorders with a complex genetic etiology. The International Molecular Genetic Study of Autism Consortium previously identified linkage loci on chromosomes 7 and 2, termed AUTS1 and AUTS5, respectively. In this study, we performed a high-density association analysis in AUTS1 and AUTS5, testing more than 3000 single nucleotide polymorphisms (SNPs) in all known genes in each region, as well as SNPs in non-genic highly conserved sequences. SNP genotype data were also used to investigate copy number variation within these regions. The study sample consisted of 127 and 126 families, showing linkage to the AUTS1 and AUTS5 regions, respectively, and 188 gender-matched controls. Further investigation of the strongest association results was conducted in an independent European family sample containing 390 affected individuals. Association and copy number variant analysis highlighted several genes that warrant further investigation, including IMMP2L and DOCK4 on chromosome 7. Evidence for the involvement of DOCK4 in autism susceptibility was supported by independent replication of association at rs2217262 and the finding of a deletion segregating in a sib-pair family.

Macrophage migration inhibitory factor and autism spectrum disorders

OBJECTIVE. Autistic spectrum disorders are childhood neurodevelopmental disorders characterized by social and communicative impairment and repetitive and stereotypical behavior. Macrophage migration inhibitory factor (MIF) is an upstream regulator of innate immunity that promotes monocyte/macrophage-activation responses by increasing the expression of Toll-like receptors and inhibiting activation-induced apoptosis. On the basis of results of previous genetic linkage studies and reported altered innate immune response in autism spectrum disorder, we hypothesized that MIF could represent a candidate gene for autism spectrum disorder or its diagnostic components. METHODS. Genetic association between autism spectrum disorder and MIF was investigated in 2 independent sets of families of probands with autism spectrum disorder, from the United States (527 participants from 152 families) and Holland (532 participants from 183 families). Probands and their siblings, when available, were evaluated with clinical instruments used for autism spectrum disorder diagnoses. Genotyping was performed for 2 polymorphisms in the promoter region of the MIF gene in both samples sequentially. In addition, MIF plasma analyses were conducted in a subset of Dutch patients from whom plasma was available. RESULTS. There were genetic associations between known functional polymorphisms in the promoter for MIF and autism spectrum disorder–related behaviors. Also, probands with autism spectrum disorder exhibited higher circulating MIF levels than did their unaffected siblings, and plasma MIF concentrations correlated with the severity of multiple autism spectrum disorder symptoms. CONCLUSIONS. These results identify MIF as a possible susceptibility gene for autism spectrum disorder. Additional research is warranted on the precise relationship between MIF and the behavioral components of autism spectrum disorder, the mechanism by which MIF contributes to autism spectrum disorder pathogenesis, and the clinical use of MIF genotyping.

Serotonin transporter intron 2 polymorphism associated with rigid-compulsive behaviors in Dutch individuals with pervasive developmental disorder

Two putatively functional polymorphisms of the serotonin transporter gene (HTT, SLC6A4) were examined for associations with risk for pervasive developmental disorders (PDDs) and specific autism phenotypes. Dutch patients diagnosed with PDD (N = 125, age range 5–20 years, DSM‐IV‐TR based criteria, ADI‐R and ADOS behavioral assessments) and their parents (N = 230) were genotyped for promoter ins/del (5‐HTTLPR) and intron 2 variable number of tandem repeats (VNTR) alleles. Using the transmission disequilibrium test (TDT), no disorder‐specific preferential transmission of promoter (long and short) or intron 2 (10‐ and 12‐repeat) alleles was observed. However, multivariate analysis of continuous autism‐related behavioral measures revealed that subjects with intron 2 12/12 genotype were significantly more impaired in the rigid‐compulsive domain (P = 0.008). Quantitative TDT (QTDT) analysis also showed significant association of the intron 2 VNTR 12‐repeat allele with rigid‐compulsive behavior (P = 0.015). These results suggest that intron 2 VNTR alleles or nearby polymorphisms in linkage disequilibrium may play a role in specific aspects of the behavioral phenotype of autism.

Linkage and candidate gene studies of autism spectrum disorders in European populations.

Over the past decade, research on the genetic variants underlying susceptibility to autism and autism spectrum disorders (ASDs) has focused on linkage and candidate gene studies. This research has implicated various chromosomal loci and genes. Candidate gene studies have proven to be particularly intractable, with many studies failing to replicate previously reported associations. In this paper, we investigate previously implicated genomic regions for a role in ASD susceptibility, using four cohorts of European ancestry. Initially, a 384 SNP Illumina GoldenGate array was used to examine linkage at six previously implicated loci. We identify linkage approaching genome-wide suggestive levels on chromosome 2 (rs2885116, MLOD=1.89). Association analysis showed significant associations in MKL2 with ASD (rs756472, P=4.31 × 10−5) and between SND1 and strict autism (rs1881084, P=7.76 × 10−5) in the Finnish and Northern Dutch populations, respectively. Subsequently, we used a second 384 SNP Illumina GoldenGate array to examine the association in seven candidate genes, and evidence for association was found in RELN (rs362780, P=0.00165). Further increasing the sample size strengthened the association with RELN (rs362780, P=0.001) and produced a second significant result in GRIK2 (rs2518261, P=0.008). Our results strengthen the case for a more detailed study of the role of RELN and GRIK2 in autism susceptibility, as well as identifying two new potential candidate genes, MKL2 and SND1.

Polymorphisms in leucine-rich repeat genes are associated with autism spectrum disorder susceptibility in populations of European ancestry

BackgroundAutism spectrum disorders (ASDs) are a group of highly heritable neurodevelopmental disorders which are characteristically comprised of impairments in social interaction, communication and restricted interests/behaviours. Several cell adhesion transmembrane leucine-rich repeat (LRR) proteins are highly expressed in the nervous system and are thought to be key regulators of its development. Here we present an association study analysing the roles of four promising candidate genes - LRRTM1 (2p), LRRTM3 (10q), LRRN1 (3p) and LRRN3 (7q) - in order to identify common genetic risk factors underlying ASDs.MethodsIn order to gain a better understanding of how the genetic variation within these four gene regions may influence susceptibility to ASDs, a family-based association study was undertaken in 661 families of European ancestry selected from four different ASD cohorts. In addition, a case-control study was undertaken across the four LRR genes, using logistic regression in probands with ASD of each population against 295 ECACC controls.ResultsSignificant results were found for LRRN3 and LRRTM3 (P < 0.005), using both single locus and haplotype approaches. These results were further supported by a case-control analysis, which also highlighted additional SNPs in LRRTM3.ConclusionsOverall, our findings implicate the neuronal leucine-rich genes LRRN3 and LRRTM3 in ASD susceptibility.

Validity of the Children’s Social Behavior Questionnaire (CSBQ) in Children with Intellectual Disability: Comparing the CSBQ with ADI-R, ADOS, and Clinical DSM-IV-TR Classification

The Children’s Social Behavior Questionnaire (CSBQ) was compared with the Autism Diagnostic Interview-Revised (ADI-R), Autism Diagnostic Observation Schedule (ADOS), and clinical classification in children with mild and moderate intellectual disability (ID), to investigate its criterion related validity. The contribution of the CSBQ to a classification of Autism Spectrum Disorder (ASD) was most specific for the subscales ‘contact’ and ‘stereotyped’, with high coherence with all three classification methods. The CSBQ may be used as a signaling, screening, or describing instrument for children with ASD and ID, as it complements other methods by adding unique information about the clinical presentation.

Urinary Excretion of 5-Hydroxyindoleacetic Acid, Serotonin and 6-Sulphatoxymelatonin in Normoserotonemic and Hyperserotonemic Autistic Individuals

Objective: A substantial proportion of individuals with autism have elevated levels of platelet serotonin (5-HT). We examined whether platelet hyperserotonemia is associated with increased gut 5-HT synthesis, altered 5-HT catabolism or altered melatonin production. Methods: Urinary excretion of 5-hydroxyindoleacetic acid (5-HIAA) and 5-HT was compared in 10 normoserotonemic and 10 hyperserotonemic age-matched autistic individuals. The relationship of urinary 6-sulfatoxymelatonin (6-SM) excretion to platelet 5-HT, and to urinary 5-HT and 5-HIAA excretion, was also examined. Results: In the hyperserotonemic group, significant increases at trend level in urinary excretion of 5-HIAA (p = 0.061) and 5-HT (p = 0.071) and a significant decrease for 6-SM were found (p = 0.027). The urinary 5-HIAA:5-HT ratio was similar in the normo- versus the hyperserotonemic groups. Conclusions: The catabolism of 5-HT does not differ in the groups, but greater exposure of the platelet to 5-HT cannot be ruled out as a cause of the platelet hyperserotonemia of autism. Although only trend level significant, the data point to a need for larger studies to examine more thoroughly the relationships between platelet hyperserotonemia, gut 5-HT synthesis and melatonin production.

Risperidone-induced weight gain in referred children with autism spectrum disorders is associated with a common polymorphism in the 5-hydroxytryptamine 2C receptor gene.

Weight gain is an important adverse effect of risperidone, but predictors of significant weight gain have yet to be identified in pediatric patients. Here, we investigated differences between age- and gender-normed body mass index-standardized z scores at baseline and after 8 weeks of open-label, flexible-dose risperidone treatment (mean dose: 1.70  mg/day) in 32 youths with pervasive developmental disorder (mean age = 8.74, range = 5-16 years) in relation to -759C/T 5-hydroxytryptamine 2C receptor (HTR2C) promoter and rs1414334 HTR2C intragenic C/G alleles, along with gender, age, and risperidone dose, using repeated measures analyses of variance. Carriers of the HTR2C promoter T allele gained an average of 0.043 ± 0.017 body mass index-standardized z scores (1.84 ± 1.51  kg) versus 0.64 ± 0.35 z (3.23 ± 1.47  kg) for non-T-allele carriers (p < 0.001). Presence of the rs1414334 C allele played no significant role. Further, weight gain appeared to be associated with younger age and higher doses of risperidone. The current preliminary findings suggest that the variant T allele of the -759C/T HTR2C promoter polymorphism is protective against risperidone-induced weight gain. Younger children and those treated with higher doses of risperidone may be at higher risk for weight gain.

Pervasive Developmental Disorder, Behavior Problems, and Psychotropic Drug Use in Children and Adolescents With Mental Retardation

OBJECTIVE. This study investigated the interrelationship between psychopharmacotherapy in general and the use of specific psychotropic drugs and pervasive developmental disorder and other behavior problems in children and adolescents with mental retardation. METHODS. A total of 862 participants 4 to 18 years of age, including all levels of mental retardation, were recruited through facilities for children with mental retardation in Friesland, the Netherlands. Information on medication was collected through parent interviews. Behavior problems were investigated with a standardized parent questionnaire (Developmental Behavior Checklist). A pervasive developmental disorder classification was based on the Pervasive Developmental Disorder in Mental Retardation Scale, completed by psychologists or teachers. Logistic regression analysis was used to investigate the relationship between the use of psychotropic drugs and pervasive developmental disorder and other behavioral problems, in the presence of possible confounders. RESULTS. One of 10 participants used psychotropic medication. The main factors associated with psychotropic drug use were pervasive developmental disorder and disruptive behavior. The level of functioning was also associated. Self-absorbed behavior was statistically significantly associated with clonidine use and disruptive behavior with stimulant use. Pervasive developmental disorder and communication problems were the main factors associated with the use of antipsychotic drugs. Age also played a role, whereas gender, living situation, and level of mental retardation did not. CONCLUSIONS. Antipsychotic drugs were associated with pervasive developmental disorder, whereas clonidine and stimulants were associated with self-absorbed and disruptive behavior, respectively. Although clonidine and risperidone are not registered for the problems reported and the other nonstimulants were only sometimes used on-label, their use was associated with specific psychiatric or behavioral problems.