Gut microbiota profiles of autism spectrum disorder and attention deficit/hyperactivity disorder: A systematic literature review

Accumulating evidence has implicated an involvement of the gut-brain axis in autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD), however with highly diverse results. This systematic review aims to describe and evaluate studies investigating the gut microbiota composition in individuals with ASD or ADHD and to evaluate if variations in gut microbiota are associated with these disorders. Twenty-four articles were identified in a systematic literature search of PubMed and Embase up to July 22, 2019. They consisted of 20 studies investigating ASD and four studies investigating ADHD. For ASD, several studies agreed on an overall difference in β-diversity, although no consistent bacterial variation between all studies was reported. For ADHD, the results were more diverse, with no clear differences observed. Several common characteristics in gut microbiota function were identified for ASD compared to controls. In contrast, highly heterogeneous results were reported for ADHD, and thus the association between gut microbiota composition and ADHD remains unclear. For both disorders, methodological differences hampered the comparison of studies.

EARLY REGULATION IN CHILDREN WHO ARE LATER DIAGNOSED WITH AUTISM SPECTRUM DISORDER. A LONGITUDINAL STUDY WITHIN THE DANISH NATIONAL BIRTH COHORT

Studies have shown that children later diagnosed with autism spectrum disorders (ASD) in their first years of life might show symptoms in main developmental areas and that these signs might be sensed by the parents. The present study investigated in a large birth cohort if children later diagnosed with ASD had deviations at 6 and 18 months in areas such as the ability to self-regulate emotions, feeding, and sleeping. The study was based on prospective information collected from 76,322 mothers who participated in the Danish National Birth Cohort. When the children reached an average age of 11 years, 973 children with ASD and a control group of 300 children with intellectual disability (IDnoASD) were identified via Danish health registries. Associations were found between short periods of breast-feeding and the children later diagnosed with ASD and IDnoASD as well as associations at 18 months to deviations in regulation of emotions and activity. The similarities in these associations emphasize how difficult it is to distinguish between diagnoses early in life.

Early development in Rett syndrome - the benefits and difficulties of a birth cohort approach

PURPOSES

Typically, early (pre-diagnostic) development in individuals later diagnosed with Rett syndrome (RTT) has been investigated retrospectively using parent reports, medical records and analysis of home videos. In recent years, prospective research designs have been increasingly applied to the investigation of early development in individuals with late phenotypical onset disorders, for example, autism spectrum disorder.

METHODS

In this study, data collected by the Danish National Birth Cohort lent itself to prospective exploration of the early development of RTT, in particular early motor-, speech-language, and socio-communicative behaviors, mood, and sleep.

RESULTS AND CONCLUSIONS

Despite limitations, this quasi prospective methodology proved promising. In order to add substantially to the body of knowledge, however, specific questions relating to peculiarites in early development could usefully be added to future cohort studies. As this involves considerable work, it may be more realistic to consider a set of indicators which point to a number of developmental disorders rather than to one.

Early development in children that are later diagnosed with disorders of attention and activity: a longitudinal study in the Danish National Birth Cohort

Not much is known about the early development in children that are later diagnosed with disorders of attention and activity (ADHD). Using prospective information collected from mothers in the Danish National Birth Cohort (DNBC), we investigated if developmental deviations in the first years of life are associated with later ADHD. In the DNBC 76,286 mothers were interviewed about their child's development and behaviour at age 6 and 18 months. At the end of follow-up, when the children were 8-14 years of age, 2034 were registered in Danish health registers with a clinical diagnosis of ADHD. The Hazard Ratio of ADHD was estimated using Cox regression model. At 6 months of age deviations in development showed associations with the child later being diagnosed with ADHD such as duration of breastfeeding, motor functioning, and incessant crying. At 18 months, many observations clearly associated with ADHD as for example the child not being able to fetch things on request [HR 3.0 (95 % CI 2.4; 3.7)], or the child being significantly more active than average [HR 2.0 (95 % CI 1.8; 2.2)]. An association to ADHD was shown, especially at 18 months, if the mother found it difficult to handle the child [HR 2.9 (95 % CI 2.4-3.5)]. However, it goes for all observations that the positive predictive values were low. Many children with ADHD showed signs of developmental deviations during the first years of their life. In general, however, ADHD cannot be identified solely on basis of the questions in DNBC.

A systematic review and meta-analysis of the long-term overall outcome of autism spectrum disorders in adolescence and adulthood

OBJECTIVE

A systematic review and meta-analysis of studies reporting on the overall outcome in terms of a global measure of adjustment in children with autistic disorders followed up in adolescence and adulthood.

METHOD

PubMed, PsycINFO, and EMBASE were systematically searched on 3rd of August 2015. Included studies were analyzed using random-effects models estimating event rates (%) and 95% confidence intervals (95%CI).

RESULTS

From 4350 records identified in the search, 15 studies covering 12 unique samples and a total of N = 828 individuals with autistic disorders were included in the analyses. An estimated 19.7% (95%CI: 14.2-26.6) had a good outcome, 31.1% (95%CI: 23.2-40.4%) a fair outcome, and 47.7% (95%CI: 36.6-59.0) a poor outcome. The meta-analysis showed strong evidence for heterogeneity. The subtype of childhood autism is a significant moderating factor on the risk of having a poor outcome at follow-up, whereas age at follow-up showed statistically significant but inconsistent associations with outcome status.

CONCLUSION

The long-term outcome of almost half of all individuals with autistic disorders is poor. The subtype of autism in childhood may be a predictor for specific long-term outcomes, but in general, little is known about the pathways and predictors.

Urbanicity and autism spectrum disorders

The etiology of autism spectrum disorders (ASD) is for the majority of cases unknown and more studies of risk factors are needed. Geographic variation in ASD occurrence has been observed, and urban residence has been suggested to serve as a proxy for etiologic and identification factors in ASD. We examined the association between urbanicity level and ASD at birth and during childhood. The study used a Danish register-based cohort of more than 800,000 children of which nearly 4,000 children were diagnosed with ASD. We found a dose-response association with greater level of urbanicity and risk of ASD. This association was found for residence at birth as well as residence during childhood. Further, we found an increased risk of ASD in children who moved to a higher level of urbanicity after birth. Also, earlier age of ASD diagnosis in urban areas was observed. While we could not directly examine the specific reasons behind these associations, our results demonstrating particularly strong associations between ASD diagnosis and post-birth migration suggest the influence of identification-related factors such as access to services might have a substantive role on the ASD differentials we observed.

The International Collaboration for Autism Registry Epidemiology (iCARE): multinational registry-based investigations of autism risk factors and trends

The International Collaboration for Autism Registry Epidemiology (iCARE) is the first multinational research consortium (Australia, Denmark, Finland, Israel, Norway, Sweden, USA) to promote research in autism geographical and temporal heterogeneity, phenotype, family and life course patterns, and etiology. iCARE devised solutions to challenges in multinational collaboration concerning data access security, confidentiality and management. Data are obtained by integrating existing national or state-wide, population-based, individual-level data systems and undergo rigorous harmonization and quality control processes. Analyses are performed using database federation via a computational infrastructure with a secure, web-based, interface. iCARE provides a unique, unprecedented resource in autism research that will significantly enhance the ability to detect environmental and genetic contributions to the causes and life course of autism.

Dysfunction of the Heteromeric KV7.3/KV7.5 Potassium Channel is Associated with Autism Spectrum Disorders

Heterozygous mutations in the KCNQ3 gene on chromosome 8q24 encoding the voltage-gated potassium channel K_V7.3 subunit have previously been associated with rolandic epilepsy and idiopathic generalized epilepsy (IGE) including benign neonatal convulsions. We identified a de novot(3;8) (q21;q24) translocation truncating KCNQ3 in a boy with childhood autism. In addition, we identified a c.1720C > T [p.P574S] nucleotide change in three unrelated individuals with childhood autism and no history of convulsions. This nucleotide change was previously reported in patients with rolandic epilepsy or IGE and has now been annotated as a very rare SNP (rs74582884) in dbSNP. The p.P574S K_V7.3 variant significantly reduced potassium current amplitude in Xenopus laevis oocytes when co-expressed with K_V7.5 but not with K_V7.2 or K_V7.4. The nucleotide change did not affect trafficking of heteromeric mutant K_V7.3/2, K_V7.3/4, or K_V7.3/5 channels in HEK 293 cells or primary rat hippocampal neurons. Our results suggest that dysfunction of the heteromeric K_V7.3/5 channel is implicated in the pathogenesis of some forms of autism spectrum disorders, epilepsy, and possibly other psychiatric disorders and therefore, KCNQ3 and KCNQ5 are suggested as candidate genes for these disorders.

Patterns of contact with hospital for children with an autism spectrum disorder: a Danish register-based study

The aim of this study was to study patterns of contact with hospital for children with autism spectrum disorder (ASD) using Danish population based register data. We included all children born in Denmark from 1994 through 2002. We found that children diagnosed with ASD had an increased rate of contact with hospital, almost regardless of the cause for the hospital contact. Given the overall association between hospital contact for various causes and ASD observed in these data, hospital data should be used cautiously in future studies searching for associations between a specific disease and ASD. If the increased rate of hospital contact overall for children with ASD is not considered, then misleading over interpretations might be made of observed associations between specific diseases and ASD.

[22q11 deletion syndrome]

22q11 deletion syndrome (formerly named CATCH22, DiGeorge, Velo-Cardio-Facial, Caylor, Kinouchi and Shprintzen syndrome) occurs in approximately 1/2000 to 4000 children. The genetic lesion is remarkably uniform, occurring mainly as 3 or 1.5 MB deletions in the 22q11.2 region. However, the clinical manifestations are variable and manifestation in several organ systems often occur. In this review we describe the various manifestations of the syndrome. Finally, we suggest strategies for diagnosing, evaluating and organizing the treatment for Danish patients with this syndrome.

A genome-wide search for alleles and haplotypes associated with autism and related pervasive developmental disorders on the Faroe Islands

The involvement of genetic factors in the etiology of autism has been clearly established. We undertook a genome-wide search for regions containing susceptibility genes for autism in 12 subjects with childhood autism and related pervasive developmental disorders (PDDs) and 44 controls from the relatively isolated population of the Faroe Islands. In total, 601 microsatellite markers distributed throughout the human genome with an average distance of 5.80 cM were genotyped, including 502 markers in the initial scan. The Faroese population structure and genetic relatedness of cases and controls were also evaluated. Based on a combined approach, including an assumption-free test as implemented in CLUMP, Fisher's exact test for specific alleles and haplotypes, and IBD(0) probability calculations, we found association between autism and microsatellite markers in regions on 2q, 3p, 6q, 15q, 16p, and 18q. The most significant finding was on 3p25.3 (P(T1)=0.00003 and P(T4)=0.00007), which was also supported by other genetic studies. Furthermore, no evidence of population substructure was found, and a higher degree of relatedness among cases could not be detected, decreasing the risk of inflated P-values. Our data suggest that markers in these regions are in linkage disequilibrium with genes involved in the etiology of autism, and we hypothesize susceptibility genes for autism and related PDDs to be localized within these regions.

The incidence and prevalence of pervasive developmental disorders: a Danish population-based study

BACKGROUND

Based on prevalence studies and the few incidence studies of pervasive developmental disorders (PDDs) the prevalence and incidence of these disorders have been claimed to be increasing.

METHOD

The annual and age-specific prevalence and incidence rates of childhood autism, atypical autism, Asperger's disorder, and pervasive developmental disorder not otherwise specified (PDD-NOS) in Denmark during the period 1971--2000 in children younger than 10 years were estimated using data from the Danish Psychiatric Central Register.

RESULTS

A total of 2.4 million children younger than 10 years were followed and 2061 cases with the PDDs studied were identified. Generally, the prevalence and incidence rates of the PDDs studied were stable until the early 1990s after which an increase in the occurrence of all disorders was seen, until 2000. The annual incidence rate per 10000 children younger than 10 years was 2.0 for childhood autism, 0.7 for atypical autism, 1.4 for Asperger's disorder, and 3.0 for PDD-NOS in 2000. We calculated a 'corrected' prevalence of childhood autism at 11.8, atypical autism at 3.3, Asperger's disorder at 4.7, and PDD-NOS at 14.6 per 10,000 children younger than 10 years on 1 January 2001.

CONCLUSIONS

We found that the estimated prevalences of the PDDs studied were probably underestimated. Furthermore, the increasing prevalence and incidence rates during the 1990s may well be explained by changes in the registration procedures and more awareness of the disorders, although a true increase in the incidence cannot be ruled out.

Thimerosal and the occurrence of autism: negative ecological evidence from Danish population-based data

OBJECTIVE

It has been suggested that thimerosal, a mercury-containing preservative in vaccines, is a risk factor for the development of autism. We examined whether discontinuing the use of thimerosal-containing vaccines in Denmark led to a decrease in the incidence of autism.

DESIGN

Analysis of data from the Danish Psychiatric Central Research Register recording all psychiatric admissions since 1971, and all outpatient contacts in psychiatric departments in Denmark since 1995.

PATIENTS

All children between 2 and 10 years old who were diagnosed with autism during the period from 1971-2000.

OUTCOME MEASURES

Annual and age-specific incidence for first day of first recorded admission with a diagnosis of autism in children between 2 and 10 years old.

RESULTS

A total of 956 children with a male-to-female ratio of 3.5:1 had been diagnosed with autism during the period from 1971-2000. There was no trend toward an increase in the incidence of autism during that period when thimerosal was used in Denmark, up through 1990. From 1991 until 2000 the incidence increased and continued to rise after the removal of thimerosal from vaccines, including increases among children born after the discontinuation of thimerosal.

CONCLUSIONS

The discontinuation of thimerosal-containing vaccines in Denmark in 1992 was followed by an increase in the incidence of autism. Our ecological data do not support a correlation between thimerosal-containing vaccines and the incidence of autism.

Analysis of transmission of novel polymorphisms in the somatostatin receptor 5 (SSTR5) gene in patients with autism

Infantile autism is a pervasive developmental disorder with a strong genetic component. The mode of inheritance appears to be complex and no specific susceptibility genes have yet been identified. Chromosome 16p13.3 may contain a susceptibility gene based on findings from genome scans and reports of chromosome abnormalities in individuals with autism. The somatostatin receptor 5 (SSTR5) gene is located on chromosome 16p13.3 and is thus a positional candidate gene for autism. SSTR5 may also be a functional candidate gene for autism because somatostatin inhibits growth hormone secretion, and increased growth hormone response has been reported in some individuals with autism. Moreover, the somatostatinergic system interacts with the dopaminergic system, which has been hypothesized to be involved in the etiology of autism; in particular, somatostatin secretion is regulated by dopamine, and the dopamine D2 receptor and the SSTR5 receptor interact to form a receptor complex with enhanced functional activity. In the present study, we tested whether the alleles of twelve new single nucleotide polymorphisms (SNPs) in the SSTR5 gene were preferentially transmitted, using the transmission disequilibrium test (TDT) in a sample of 79 trios with autism (18 from Denmark and 61 from France). Furthermore, we combined four missense SNPs into haplotypes and searched for preferential transmission using the program TRANSMIT. No significant preferential transmission of the alleles and haplotypes of the twelve SNPs was found. Our results do not suggest the SSTR5 gene as a susceptibility gene for autism.

Medical disorders among inpatients with autism in Denmark according to ICD-8: a nationwide register-based study

Possible associations between autism and specific medical disorders have been suggested, and this could be of relevance in the clinical examination and treatment of patients and may help to identify factors involved in the etiology or pathophysiology of autism. Two population-based Danish registers were used to investigate the occurrence of medical disorders in patients with autism according to ICD-8 and in a matched control sample. A total of 29 of the 244 patients (11.9%) diagnosed with autism had one or more medical disorders. In contrast to previous studies, we did not find an increased occurrence of almost any medical disorders. A highly significant increased frequency of congenital malformations was found, which may indicate abnormalities in embryogenesis in the etiology of autism.