A case-control study of obstetric complications and later autistic disorder

The association between post-term births and autism spectrum disorders: an updated systematic review and meta-analysis

BACKGROUND

This study aimed to conduct a meta-analysis to determine whether post-term birth has an increased risk of ASD.

MATERIALS AND METHODS

To retrieve eligible studies regarding the effect of post-term and ASD in children, major databases including PubMed, Scopus, and Web of Science were searched. A random effect model was used for meta-analysis. For assessing the quality of included studies, the GRADE checklist was used.

RESULTS

In total, 18 records were included with 1,412,667 sample populations from 12 countries. The pooled estimates of RR and OR showed a significant association between post-term birth and ASD among children, respectively (RR = 1.34, 95% CI 1.10 to 1.58) and (OR = 1.47, 95% CI 1.03 to 1.91). There was no heterogeneity among the studies that reported the risk of ASD among children based on RR (I2 = 6.6%, P = 0.301). There was high heterogeneity in the studies reported risk of ASD based on OR (I2 = 94.1%, P = 0.000).

CONCLUSION

Post-term births still occur relatively frequently (up to 5-10%) even in developed countries. Our results showed that post-term birth is an increased risk of ASD, although high heterogeneity was found among the studies reported based on adjusted and crude forms, however, after subgroup analysis by gender, this heterogeneity disappeared among males.

Maternal and neonatal risk factors for autism spectrum disorder: A case-control study from Egypt

Background

The prevalence of autism spectrum disorder (ASD) has been increasing steadily in Egypt and worldwide. Detecting risk factors for ASD could help initiate screening and risk prevention approaches. Herein, this study aimed to detect several maternal and neonatal risk factors for ASD in Egypt.

Methods

In this case-control study, mothers of children with ASD who were visiting Beni-Suef University Hospital in Egypt (n = 268) were compared to mothers of children without ASD attending one primary school with a kindergarten (n = 504) regarding their preconception, conception, and postconception characteristics. Data were collected using a self-administered questionnaire. The odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to investigate the possible associations between the collected data and the odds of ASD.

Results

In the multivariable-adjusted models, urban residence: OR (95% CI) = 2.33 (1.60–3.38), relative father: 2.63 (1.74–3.96), history of diabetes: 5.98 (1.99–17.97), previous abortion: 2.47 (1.20–13.38), assisted fertility: 4.01 (1.20–13.38), family history of ASD: 7.24 (2.00–26.24), multiple pregnancy: 11.60 (2.54–53.07), exposure to passive smoking during pregnancy: 2.95 (1.86–4.68), vaginal bleeding during pregnancy: 3.10 (1.44–6.67), hypertension with pregnancy: 3.64 (1.06–12.51), preterm labor: 2.64 (1.26–5.57), neonatal convulsions: 14.88 (5.01–44.20), and admission to neonatal intensive care unit 2.13: (1.21–3.74) were associated with the increased odds of ASD. On the other hand, the intake of vitamins during pregnancy: 0.09 (0.06–0.16) and C-section: 0.44 (0.27–0.70) were associated with the decreased odds of ASD.

Conclusion

This study detected several maternal and neonatal risk factors for ASD in Egyptian children.

Prenatal, perinatal, and postnatal factors associated with autism: A meta-analysis

BACKGROUND

The aim of this meta-analysis was to investigate the prenatal, perinatal, and postnatal risk factors for children autism.

METHODS

PubMed, Embase, Web of Science were used to search for studies that examined the prenatal, perinatal, and postnatal risk factors for children autism. A fixed-effects model or random-effects model was used to pool the overall effect estimates.

RESULTS

Data from 37,634 autistic children and 12,081,416 nonautistic children enrolled in 17 studies were collated. During the prenatal period, the factors associated with autism risk were maternal and paternal age≥35 years, mother's and father's race: White and Asian, gestational hypertension, gestational diabetes, maternal and paternal education college graduate+, threatened abortion, and antepartum hemorrhage. During perinatal period, the factors associated with autism risk were caesarian delivery, gestational age≤36 weeks, parity≥4, spontaneous labor, induced labor, no labor, breech presentation, preeclampsia, and fetal distress. During the postnatal period, the factors associated with autism risk were low birth weight, postpartum hemorrhage, male gender, and brain anomaly. Parity≥4 and female were associated with a decreased risk of autism. In addition, exposure to cigarette smoking, urinary infection, mother's and father's race: Black and Hispanic, mother's country of birth outside Europe and North America, umbilical cord around neck, premature membrane rupture, 5-minutes Apgar score<7, and respiratory infection were not associated with increased risk of autism.

CONCLUSION

The present meta-analysis confirmed the relation between some prenatal, perinatal, and postnatal factors with autism. All these factors were examined individually, thus it was still unclear that whether these factors are causal or play a secondary role in the development of autism. Further studies are needed to verify our findings, and investigate the effects of multiple factors on autism, rather than the single factor.

Modeling neurodevelopmental cognitive deficits in tasks with cross-species translational validity

Numerous psychiatric disorders whose cognitive dysfunction links to functional outcome have neurodevelopmental origins including schizophrenia, autism and bipolar disorder. Treatments are needed for these cognitive deficits, which require development using animal models. Models of neurodevelopmental disorders are as varied and diverse as the disorders themselves, recreating some but not all aspects of the disorder. This variety may in part underlie why purported procognitive treatments translated from these models have failed to restore functioning in the targeted patient populations. Further complications arise from environmental factors used in these models that can contribute to numerous disorders, perhaps only impacting specific domains, while diagnostic boundaries define individual disorders, limiting translational efficacy. The Research Domain Criteria project seeks to 'develop new ways to classify mental disorders based on behavioral dimensions and neurobiological measures' in hopes of facilitating translational research by remaining agnostic toward diagnostic borders derived from clinical presentation in humans. Models could therefore recreate biosignatures of cognitive dysfunction irrespective of disease state. This review highlights work within the field of neurodevelopmental models of psychiatric disorders tested in cross-species translational cognitive paradigms that directly inform this newly developing research strategy. By expounding on this approach, the hopes are that a fuller understanding of each model may be attainable in terms of the cognitive profile elicited by each manipulation. Hence, conclusions may begin to be drawn on the nature of cognitive neuropathology on neurodevelopmental and other disorders, increasing the chances of procognitive treatment development for individuals affected in specific cognitive domains.

Parental concerns, socioeconomic status, and the risk of autism spectrum conditions in a population-based study

A total number of 11,635 screening packs were distributed to 5-10 year-old children in 136 schools in Cambridgeshire to investigate the associations between levels of parental concern (none/minor/strong), socioeconomic status and the risk of having Autism Spectrum Conditions (ASC). The variables for investigating associations and possible confounders were extracted for analysis, including parental concern question score, SES, age of the child, sex, maternal age at birth, paternal age at birth, mother's age of leaving education, father's age of leaving education, birth order and the number of children in the family. The SES, age of the child, sex and mother's age at leaving education were associated with parental concern. Parents with higher SES reported higher levels of concern (Chi-square = 11.8; p = 0.02). However, a higher SES was not associated with the risk of having ASC (p = 0.50). After adjusting for potential confounders, the odds of children meeting ASC criteria whose parents had reported strong parental concern were 8.5 times (odds ratio: 8.5; 95%CI: 4.5, 16.2; p < 0.001) the odds of children having ASC whose parents reported minor concern. No child met ASC criteria where parents expressed no concerns. Parents with higher social class express more concerns than those from lower social classes. However, the concerns reported by parents in higher SES did not appear to be specific for ASC as there was no relationship between ASC and SES.

Parental age and the risk of autism spectrum disorders: findings from a Swedish population-based cohort

BACKGROUND

The objectives of this study were to examine the independent and dependent associations of maternal and paternal age and risk of offspring autism spectrum disorders (ASD), with and without intellectual disability (ID).

METHODS

The sample consisted of 417 303 Swedish children born 1984-2003. ASD case status (N = 4746) was ascertained using national and regional registers. Smoothing splines in generalized additive models were used to estimate associations of parental age with ASD.

RESULTS

Whereas advancing parental age increased the risk of child ASD, maternal age effects were non-linear and paternal age effects were linear. Compared with mothers at the median age 29 years, those <29 had similar risk, whereas risk increased after age 30, with an odds ratio (OR) of 1.75 [95% (CI): 1.63-1.89] at ages 40-45. For fathers, compared with the median age of 32 years, the OR for ages 55-59 was 1.39 (1.29-1.50). The risk of ASD was greater for older mothers as compared with older fathers. For example, mothers aged 40-45 (≥97.2th percentile) had an estimated 18.63 (95% CI: 17.25-20.01) ASD cases per 1000 births, whereas fathers aged 55-59 (≥99.7th percentile) had 16.35 (95% CI: 15.11-17.58) ASD cases per 1000 births. In analyses stratified by co-parental age, increased risk due to advancing paternal age was evident only with mothers ≤35 years. In contrast, advancing maternal age increased risk regardless of paternal age. Advancing parental age was more strongly associated with ASD with ID, compared with ASD without ID.

CONCLUSIONS

We confirm prior findings that advancing parental age increases risk of ASD, particularly for ASD with ID, in a manner dependent on co-parental age. Although recent attention has emphasized the effects of older fathers on ASD risk, an increase of n years in maternal age has greater implications for ASD risk than a similar increase in paternal age.

Prenatal, perinatal and neonatal risk factors of Autism Spectrum Disorder: a comprehensive epidemiological assessment from India

Incidence of Autism Spectrum Disorder (ASD) is increasing across the globe and no data is available from India regarding the risk factors of ASD. In this regard a questionnaire based epidemiological assessment was carried out on prenatal, perinatal and neonatal risk factors of ASD across 8 cities in India. A retrospective cohort of 942 children was enrolled for the study. 471 children with ASD, under age of 10, were analyzed for pre-, peri-, and neonatal factors and were compared with the observations from equal number of controls. The quality control of the questionnaire and data collection was done thoroughly and the observations were computed statistically. A total of 25 factors were evaluated by unadjusted and adjusted analysis in this study. Among the prenatal factors considered, advanced maternal age, fetal distress and gestational respiratory infections were found to be associated with ASD and had an odds ratio of 1.8. Evaluation of perinatal and neonatal risk factors showed labor complications, pre-term birth, neonatal jaundice, delayed birth cry and birth asphyxia to be associated with ASD with an odds ratio greater than 1.5. This important study, first of its kind in Indian population gives a firsthand account of the relation of pre-, peri- and neonatal risk factors on ASD from an ethnically and socially diverse country like India, the impact of which was unknown earlier. This advocates additional focused investigations on physiological and genetic changes contributed by these risk factor inducing environments.

Lower birth weight indicates higher risk of autistic traits in discordant twin pairs

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disorder of complex etiology. Although strong evidence supports the causal role of genetic factors, environmental risk factors have also been implicated. This study used a co-twin-control design to investigate low birth weight as a risk factor for ASD.

METHOD

We studied a population-based sample of 3715 same-sex twin pairs participating in the Child and Adolescent Twin Study of Sweden (CATSS). ASD was assessed using a structured parent interview for screening of ASD and related developmental disorders, based on DSM-IV criteria. Birth weight was obtained from medical birth records maintained by the Swedish Medical Birth Registry.

RESULTS

Twins lower in birth weight in ASD-discordant twin pairs (n=34) were more than three times more likely to meet criteria for ASD than heavier twins [odds ratio (OR) 3.25]. Analyses of birth weight as a continuous risk factor showed a 13% reduction in risk of ASD for every 100 g increase in birth weight (n=78). Analysis of the effect of birth weight on ASD symptoms in the entire population (most of whom did not have ASD) showed a modest association. That is, for every 100 g increase in birth weight, a 2% decrease in severity of ASD indexed by scores on the Autism - Tics, attention-deficit hyperactivity disorder (AD/HD), and other Comorbidities (A-TAC) inventory would be expected in the sample as a whole.

CONCLUSIONS

The data were consistent with the hypothesis that low birth weight confers risk to ASD. Thus, although genetic effects are of major importance, a non-genetic influence associated with birth weight may contribute to the development of ASD.

Pre-, peri- and neonatal risk factors for autism

OBJECTIVE

To identify pre-, peri- and neonatal risk factors for pervasive developmental disorders (PDD).

METHODS

We searched the Medline database through March 2011 for relevant case-control and population-based studies on pre-, peri- and neonatal hazards related to PDD, including autism. We identified 85 studies for this review. Data were extracted systematically and organized according to risk factors related to family history, pregnancy, gestational age, delivery, birth milestones and the neonate's condition at birth.

RESULTS

During the prenatal period, risk factors for PDD were advanced maternal or paternal ages, being firstborn vs. third or later, maternal prenatal medication use and mother's status as foreign born. During the perinatal and neonatal periods, the risk factors for PDD were preterm birth, breech presentation, planned cesarean section, low Apgar scores, hyperbilirubinemia, birth defect and a birthweight small for gestational age. The influence of maternal pre-eclampsia, diabetes, vomiting, infections and stress during pregnancy requires further study in order to determine risk for PDD.

DISCUSSION

Despite evidence for the association of some pre-, peri- and neonatal risk factors associated with PDD, it remains unclear whether these risks are causal or play a secondary role in shaping clinical expression in individuals with genetic vulnerability. A plausible hypothsesis is that improvements in obstetric and neonatal management have led to an increased rate of survivors with pre-existing brain damage. Given the variety of risk factors, we propose that future studies should investigate combinations of multiple factors, rather than focusing on a single factor.

Have secular changes in perinatal risk factors contributed to the recent autism prevalence increase? Development and application of a mathematical assessment model

BACKGROUND

A 57% increase in the U.S. prevalence of autism spectrum disorders (ASD) for 8-year-old children born in 1994 versus 1998 was recently reported.

METHODS

To quantify the possible contributions of given risk/predictive factors on the recent ASD prevalence increase, we formulated a mathematical model based on the baseline risk factor prevalence (RFP), the proportionate change in RFP (cRFP), and the magnitude of the association between the risk factor and ASD [estimated relative risk (RR)]. We applied this model to several pregnancy-related factors (preterm, very preterm, low and very low birth weight, multiple birth, cesarean delivery, breech presentation, and assisted reproductive technology use). RFP and cRFP estimates for each factor were obtained from U.S. population-based surveillance datasets. Estimated RRs were obtained from a series of systematic literature reviews.

RESULTS

We estimate that each risk factor examined, alone or in various combinations, accounted for a very small proportion (<1%) of the ASD increase. Additionally, hypothetical scenarios indicate RFP, cRFP, and RR all need to be sizable for a risk factor to appreciably influence ASD prevalence.

CONCLUSIONS

Thus, although various pregnancy factors have been found to be associated with ASDs, the contribution of many of these factors to the recently observed ASD increase is likely minimal.

Perinatal and neonatal risk factors for autism: a comprehensive meta-analysis

BACKGROUND

The etiology of autism is unknown, although perinatal and neonatal exposures have been the focus of epidemiologic research for over 40 years.

OBJECTIVE

To provide the first review and meta-analysis of the association between perinatal and neonatal factors and autism risk.

METHODS

PubMed, Embase, and PsycInfo databases were searched for studies that examined the association between perinatal and neonatal factors and autism through March 2007. Forty studies were eligible for the meta-analysis. For each exposure, a summary effect estimate was calculated using a random-effects model. Heterogeneity in effect estimates across studies was examined, and, if found, a meta-regression was conducted to identify measured methodological factors that could explain between-study variability.

RESULTS

Over 60 perinatal and neonatal factors were examined. Factors associated with autism risk in the meta-analysis were abnormal presentation, umbilical-cord complications, fetal distress, birth injury or trauma, multiple birth, maternal hemorrhage, summer birth, low birth weight, small for gestational age, congenital malformation, low 5-minute Apgar score, feeding difficulties, meconium aspiration, neonatal anemia, ABO or Rh incompatibility, and hyperbilirubinemia. Factors not associated with autism risk included anesthesia, assisted vaginal delivery, postterm birth, high birth weight, and head circumference.

CONCLUSIONS

There is insufficient evidence to implicate any 1 perinatal or neonatal factor in autism etiology, although there is some evidence to suggest that exposure to a broad class of conditions reflecting general compromises to perinatal and neonatal health may increase the risk. Methodological variations were likely sources of heterogeneity of risk factor effects across studies.

Prenatal and perinatal risk factors for autism in China

We conducted a case–control study using 190 Han children with and without autism to investigate prenatal and perinatal risk factors for autism in China. Cases were recruited through public special education schools and controls from regular public schools in the same region (Tianjin), with frequency matching on sex and birth year. Unadjusted analyses identified seven prenatal and seven perinatal risk factors significantly associated with autism. In the adjusted analysis, nine risk factors showed significant association with autism: maternal second-hand smoke exposure, maternal chronic or acute medical conditions unrelated to pregnancy, maternal unhappy emotional state, gestational complications, edema, abnormal gestational age (<35 or >42 weeks), nuchal cord, gravidity >1, and advanced paternal age at delivery (>30 year-old).

Exploring the relation between prenatal and neonatal complications and later autistic-like features in a representative community sample of twins

Prenatal and neonatal events were reported by parents of 13,690 eighteen-month-old twins enrolled in the Twins Early Development Study, a representative community sample born in England and Wales. At ages 7-8, parents and teachers completed questionnaires on social and nonsocial autistic-like features and parents completed the Childhood Asperger Syndrome Test. Correlations between prenatal and neonatal events and autistic-like features were weak, both in the whole sample (r = .00-.07) and at the 5% quantitative extreme (phenotypic group correlations = .01-.11), after controlling for socioeconomic status and cognitive ability. Neonatal problems showed modest heritability (13%-14%) and significant shared and nonshared environmental influences (55%-59% and 28%-31%, respectively). Differences in identical twins' neonatal problems correlated weakly with their difference scores on autistic-like features (r = .01-.06).

Socioeconomic inequality in the prevalence of autism spectrum disorder: evidence from a U.S. cross-sectional study

BACKGROUND

This study was designed to evaluate the hypothesis that the prevalence of autism spectrum disorder (ASD) among children in the United States is positively associated with socioeconomic status (SES).

METHODS

A cross-sectional study was implemented with data from the Autism and Developmental Disabilities Monitoring Network, a multiple source surveillance system that incorporates data from educational and health care sources to determine the number of 8-year-old children with ASD among defined populations. For the years 2002 and 2004, there were 3,680 children with ASD among a population of 557,689 8-year-old children. Area-level census SES indicators were used to compute ASD prevalence by SES tertiles of the population.

RESULTS

Prevalence increased with increasing SES in a dose-response manner, with prevalence ratios relative to medium SES of 0.70 (95% confidence interval [CI] 0.64, 0.76) for low SES, and of 1.25 (95% CI 1.16, 1.35) for high SES, (P<0.001). Significant SES gradients were observed for children with and without a pre-existing ASD diagnosis, and in analyses stratified by gender, race/ethnicity, and surveillance data source. The SES gradient was significantly stronger in children with a pre-existing diagnosis than in those meeting criteria for ASD but with no previous record of an ASD diagnosis (p<0.001), and was not present in children with co-occurring ASD and intellectual disability.

CONCLUSIONS

The stronger SES gradient in ASD prevalence in children with versus without a pre-existing ASD diagnosis points to potential ascertainment or diagnostic bias and to the possibility of SES disparity in access to services for children with autism. Further research is needed to confirm and understand the sources of this disparity so that policy implications can be drawn. Consideration should also be given to the possibility that there may be causal mechanisms or confounding factors associated with both high SES and vulnerability to ASD.

Paternal age increases the risk for autism in an Iranian population sample

Background

Autism is a neurodevelopmental disorder which is known to have a strong genetic component and is most likely oligogenic. However, the necessary role of environmental factors has been well documented. Prior research suggests that parental characteristics, such as age and level of education, may be associated with a risk of autism. Parental age has been shown to be associated with many disorders, such as schizophrenia, childhood cancer and fetal death. However, results from studies of parental age and autism are inconsistent.

Methods

In the present study, we investigated the association of autism with parental age in 179 autism cases and 1611 matched cohort children from Iran. Each case was matched with nine cohort controls on parental education, sex, order of birth, consanguineous marriage, urbanism and province of residence. The Cox regression model was used to carry out conditional logistic regression on the matched data.

Results

There was a significant association between higher paternal age, but not maternal age, and an increasing risk of autism. An analysis of the combined effect of parental age and education also revealed that parents with higher education had an increased risk of having autistic children, with a dose-response effect of parental age.

Conclusions

This study, which is the first epidemiological study of autism in Iran, provides evidence of the association of paternal age and risk of autism.

Medical conditions in autism spectrum disorders

Autism spectrum disorder (ASD) is a behaviourally defined syndrome where the etiology and pathophysiology is only partially understood. In a small proportion of children with the condition, a specific medical disorder is identified, but the causal significance in many instances is unclear. Currently, the medical conditions that are best established as probable causes of ASD include Fragile X syndrome, Tuberous Sclerosis and abnormalities of chromosome 15 involving the 15q11-13 region. Various other single gene mutations, genetic syndromes, chromosomal abnormalities and rare de novo copy number variants have been reported as being possibly implicated in etiology, as have several ante and post natal exposures and complications. However, in most instances the evidence base for an association with ASD is very limited and largely derives from case reports or findings from small, highly selected and uncontrolled case series. Not only therefore, is there uncertainty over whether the condition is associated, but the potential basis for the association is very poorly understood. In some cases the medical condition may be a consequence of autism or simply represent an associated feature deriving from an underlying shared etiology. Nevertheless, it is clear that in a growing proportion of individuals potentially causal medical conditions are being identified and clarification of their role in etio-pathogenesis is necessary. Indeed, investigations into the causal mechanisms underlying the association between conditions such as tuberous sclerosis, Fragile X and chromosome 15 abnormalities are beginning to cast light on the molecular and neurobiological pathways involved in the pathophysiology of ASD. It is evident therefore, that much can be learnt from the study of probably causal medical disorders as they represent simpler and more tractable model systems in which to investigate causal mechanisms. Recent advances in genetics, molecular and systems biology and neuroscience now mean that there are unparalleled opportunities to test causal hypotheses and gain fundamental insights into the nature of autism and its development.

Prenatal risk factors for autism: comprehensive meta-analysis

BACKGROUND

The aetiology of autism is unknown, although prenatal exposures have been the focus of epidemiological research for over 40 years.

AIMS

To provide the first quantitative review and meta-analysis of the association between maternal pregnancy complications and pregnancy-related factors and risk of autism.

METHOD

PubMed, Embase and PsycINFO databases were searched for epidemiological studies that examined the association between pregnancy-related factors and autism. Forty studies were eligible for inclusion in the meta-analysis. Summary effect estimates were calculated for factors examined in multiple studies.

RESULTS

Over 50 prenatal factors have been examined. The factors associated with autism risk in the meta-analysis were advanced parental age at birth, maternal prenatal medication use, bleeding, gestational diabetes, being first born v. third or later, and having a mother born abroad. The factors with the strongest evidence against a role in autism risk included previous fetal loss and maternal hypertension, proteinuria, pre-eclampsia and swelling.

CONCLUSIONS

There is insufficient evidence to implicate any one prenatal factor in autism aetiology, although there is some evidence to suggest that exposure to pregnancy complications may increase the risk.

Prenatal, perinatal, and neonatal factors associated with autism spectrum disorders

OBJECTIVE

To investigate prenatal, perinatal, and neonatal risk factors for autism spectrum disorders by using participants identified through broad ascertainment and reliable classification methods.

METHODS

The targeted population was 8-year-old children born in 1994 and residing in 1 of the 3 most populous counties in Utah who were identified as having an autism spectrum disorder on the basis of methodology used by the 2002 Autism and Developmental Disabilities Monitoring Network. Of those identified, 132 children (115 boys, 17 girls) had birth certificate records available. Each child was matched by gender and birth year to 100 controls (11 500 boys, 1700 girls) from the birth certificate database in a nested case-control design. Birth certificate records of participants and controls were surveyed for 23 potentially pathologic prenatal, perinatal, and neonatal factors.

RESULTS

The prenatal factors that occurred significantly more frequently among children with autism spectrum disorders were advanced maternal age and parity. Increased duration of education among mothers of children with autism spectrum disorders was small but statistically significant. Significant perinatal factors were breech presentation and primary cesarean delivery. When corrected for breech presentation, a known indication for cesarean delivery, the association between primary cesarean delivery and autism spectrum disorders was eliminated. There were no significant associations found between autism spectrum disorders and neonatal factors.

CONCLUSIONS

In the absence of other complications suggesting fetal distress, the association between breech presentation and autism spectrum disorders in this study suggests a shared etiology rather than causal relationship. Additional investigation focused on both genetic and environmental factors that link these autism spectrum disorder risk factors individually or collectively is needed.

Birth weight and gestational age characteristics of children with autism, including a comparison with other developmental disabilities

OBJECTIVES

The objectives of this study were to compare the birth weight and gestational age distributions and prevalence rates of autism with those of other developmental disabilities and to estimate the birth weight-and gestational age-specific risks for autism.

METHODS

For the first objective, a retrospective cohort of children born in Atlanta, Georgia, in 1981-1993 who survived to 3 years of age was identified through vital records. Children in the cohort who had developmental disabilities (autism, mental retardation, cerebral palsy, hearing loss, or vision impairment) and were still residing in metropolitan Atlanta at 3 to 10 years of age were identified through the Metropolitan Atlanta Developmental Disabilities Surveillance Program. A nested case-control sample from the cohort was used for the second objective; all cohort children identified with autism were case participants, and control participants were cohort children who were not identified as having developmental disabilities or receiving special education services.

RESULTS

The prevalence of autism in low birth weight or preterm children was markedly lower than those of other developmental disabilities. In multivariate analyses, birth weight of <2500 g and preterm birth at <33 weeks' gestation were associated with an approximately twofold increased risk for autism, although the magnitude of risk from these factors varied according to gender (higher in girls) and autism subgroup (higher for autism accompanied by other developmental disabilities). For example, a significant fourfold increased risk was observed in low birth weight girls for autism accompanied by mental retardation, whereas there was no significantly increased risk observed in low birth weight boys for autism alone.

CONCLUSIONS

Gender and autism subgroup differences in birth weight and gestational age, resulting in lower gender ratios with declining birth weight or gestational age across all autism subgroups, might be markers for etiologic heterogeneity in autism.

Outcome after intrapartum hypoxic ischaemia at term

We consider the range of childhood disabilities that have been attributed to perinatal hypoxic ischaemia at term and review the strength of evidence for each. The strongest evidence is for a causal link between acute profound hypoxic ischaemia and dyskinetic tetraplegic cerebral palsy (CP). Hemiplegic CP is not usually due to a perinatal hypoxic ischaemic insult at term; an important cause is focal cerebral infarction or 'stroke'. Characteristically, diplegic CP is seen in ex-preterm children with periventricular leukomalacia. Ataxic CP is unlikely to be due to perinatal asphyxia. Recent careful follow-up studies have shown that childhood survivors of perinatal hypoxic ischaemia are at risk for cognitive deficits even in the absence of functional motor disorders. There is no evidence that, in isolation, either attention deficit hyperactivity disorder or autism is caused by hypoxic ischaemia. As effective neuroprotective therapies are introduced, notably cooling, it is possible that the prevalence of CP may be reduced.

Parental ages at birth of children with pervasive developmental disorders are higher than those of children in the general population

To examine whether parental ages at birth of children with pervasive developmental disorders (PDD) are elevated, maternal/paternal ages at birth of 309 PDD children born in 1993-2003 (mean age, 8.4 years) were compared with those of children in the Japanese national statistics (general population). The mean maternal/paternal ages (years) at birth of PDD children of 31.7/34.6 were significantly higher even than the highest mean maternal/paternal ages at birth of children of 31.2/33.6 in the national statistics in 2003. This first Japanese study to report elevated parental ages at birth of PDD children underscores the need of further extensive studies.

beta2-Adrenergic receptor gene variants and risk for autism in the AGRE cohort

The beta2-adrenergic receptor is part of the catecholamine system, and variants at two polymorphic sites in the gene coding for the receptor (ADRB2) confer increased activity. Overstimulation of this receptor may alter brain development, and has been linked to autism in non-identical twins. The objective of this study was to determine whether alleles in ADRB2 are associated with diagnosis of autism in the Autism Genetic Resource Exchange (AGRE) population. Three hundred and thirty-one independent autism case-parent trios were included in the analysis. Subjects were genotyped at activity-related polymorphisms rs1042713 (codon 16) and rs1042714 (codon 27). Association between autism and genotypes at each polymorphic site was tested using genotype-based transmission disequilibrium tests, and effect modification by family and pregnancy characteristics was evaluated. Sensitivity to designation of the proband in each family was assessed by performing 1000 repeats of the analysis selecting affected children randomly. A statistically significant OR of 1.66 for the Glu27 homozygous genotype was observed. Increased associations with this genotype were observed among a subset of Autism Diagnostic Observation Schedule confirmed cases and a subset reporting experience of pregnancy-related stressors. In conclusion, the Glu27 allele of the ADRB2 gene may confer increased risk of autism and shows increased strength with exposure to pregnancy related stress.

Perinatal risk factors and infantile autism

OBJECTIVE

Suboptimal conditions during pregnancy and birth have been suggested as a cause of infantile autism. We have studied the association between obstetric factors and infantile autism.

METHOD

A population-based, matched case-control study of infantile autism. Conditional logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (CI).

RESULTS

The risk of infantile autism was increased for mothers aged >35 years, with foreign citizenship, and mothers who used medicine during pregnancy. A higher risk of infantile autism was seen among children with low birth weight and with congenital malformations. Birth interventions, pathological cardiotocography, green amnion fluid and acidosis during delivery were not associated with increased risk for infantile autism.

CONCLUSION

Our findings suggest that suboptimal birth conditions are not an independent risk factor for infantile autism. A high prevalence of low birth weight and birth defects among autism cases seems to explain the suboptimal birth outcome.

Brief Report: Effect of Maternal Age on Severity of Autism

The etiology of autism is complex, consisting of unknown genetic and environmental factors. Previous studies have revealed that maternal age is increased in autism compared to controls, making it a possible risk factor. This study examined the effects of maternal age on autism severity using IQ as a measure of cognitive severity and selected subtests of the Child Behavior Checklist (CBCL) as measures of social severity. A sample of 154 subjects with autism spectrum disorders was obtained from the Stanford Neuropsychiatry/Pervasive Developmental Disorder (PDD) clinic. Results indicate that there is no relationship between IQ or selected CBCL subtests and maternal age, suggesting that maternal age does not influence the severity of autism as measured by these indicators.

Sociodemographic Risk Factors for Autism in a US Metropolitan Area

The present study examined the association between autism and sociodemographic factors, overall and in subgroups of children with autism with and without mental retardation (Autism/MR and Autism/No MR, respectively); the association was further examined in subanalyses by child's source of ascertainment to assess the presence of ascertainment bias. In the main analyses, one marker of higher social class (higher median family income) was significantly associated with autism overall. Both markers of higher social class (higher maternal education and higher median family income) were significantly associated with autism/no MR, but not associated with autism/MR. In the subanalyses, associations with social class varied by ascertainment source. Future studies should consider phenotypic subgroups of children with autism and must consider potential ascertainment bias.

Sibling risk of pervasive developmental disorder estimated by means of an epidemiologic survey in Nagoya, Japan

Broad-spectrum autism, referred to as pervasive developmental disorder (PDD), may be associated with genetic factors. We examined 241 siblings in 269 Japanese families with affected children. The sibling incidence of PDD was 10.0% whereas the prevalence of PDD in the general population in the same geographic region was 2.1%. Both of these rates are higher than those reported previously, probably because of the expanded clinical criteria applied. The prevalence in males of the general population was 3.3% and that in females was 0.82%. The sibling incidences were 7.7 and 20.0% for families in which the probands were male and female, respectively. Because the reversed sex ratios correspond to the general rule for a multifactorial threshold model, we suggest that most PDD cases result from the cumulative effects of multiple factors (mostly genetic). The sibling incidences were 0 and 10.9% for families in which the proband had low and normal birth-weight, respectively, suggesting the risk is lower in families with low-birth-weight probands.

Effects of familial risk factors and place of birth on the risk of autism: a nationwide register-based study

BACKGROUND

The etiology of autism is unknown. A strong genetic component has been detected but non-genetic factors may also be involved in the etiology.

METHODS

We used data from the Danish Psychiatric Central Register and the Danish Civil Registration System to study some risk factors of autism, including place of birth, parental place of birth, parental age, family history of psychiatric disorders, and paternal identity.

RESULTS

A total of 943,664 children younger than ten years were followed from 1994 to 2001; of those, 818 children developed autism. The highest risks of autism were found in siblings of children with autism, or Asperger's syndrome and other pervasive developmental disorders (PDDs), with relative risks of 22 and 13, respectively. The relative risk of autism in the child was about twice as high if the mother had been diagnosed with a psychiatric disorder. The risk of autism was associated with increasing degree of urbanisation of the child's place of birth and with increasing paternal, but not maternal, age. An increased relative risk of 1.4 was found if the mother was born outside Europe, and in children of parents who were born in different countries.

CONCLUSIONS

The highest risk of autism was found in families with a history of autism, or Asperger's syndrome and other PDDs in siblings, supporting the commonly accepted knowledge that genetic factors are involved in the etiology of autism.

Risks for severe mental retardation occurring in isolation and with other developmental disabilities

Individual and maternal characteristics as potential risk factors for having severe mental retardation (SMR) occurring with and without cerebral palsy (CP), epilepsy, or a pervasive developmental disorder (PDD) were explored among a cohort of 119,404 children without Down syndrome born in the California Central Valley in 1992 and 1993. Unadjusted and adjusted relative risks (RRs) and their 95% confidence intervals (CIs) based on the Poisson distribution were used to estimate the risks associated with each individual and maternal factor studied for each SMR diagnostic category. The most notable increased risks for SMR occurring in isolation or with CP or epilepsy was for children born low-birth-weight or preterm who were at a substantially increased risk (RRs 2.6-9.9). In contrast, the risk of SMR occurring with a PDD was the greatest among males compared to females (RR = 3.4, 95% CI 1.5, 7.9), Blacks compared to Whites (RR = 5.1, 95% CI 1.7, 15.5), and Asians compared to Whites (RR = 3.9, 95% CI 1.3, 12.0). Etiologic heterogeneity when SMR occurs with a PDD was suggested.

Descriptive epidemiology of autism in a California population: who is at risk?

We investigated the association between selected infant and maternal characteristics and autism risk. Children with autism born in California in 1989-1994 were identified through service agency records and compared with the total population of California live births for selected characteristics recorded on the birth certificate. Multivariate models were used to generate adjusted risk estimates. From a live birth population of more than 3.5 million, 4381 children with autism were identified. Increased risks were observed for males, multiple births, and children born to black mothers. Risk increased as maternal age and maternal education increased. Children born to immigrant mothers had similar or decreased risk compared with California-born mothers. Environmental factors associated with these demographic characteristics may interact with genetic vulnerability to increase the risk of autism.

Perinatal risk factors for infantile autism

BACKGROUND

Etiologic hypotheses in infantile autism suggest a strong genetic component, as well as possible environmental risks linked to early fetal development. We evaluated the association of maternal, pregnancy, delivery, and infant characteristics and risk of infantile autism.

METHODS

We conducted a case-control study nested within a population-based cohort (all Swedish children born in 1974-1993). We used prospectively recorded data from the Swedish Birth Register, which were individually linked to the Swedish Inpatient Register. Cases were 408 children (321 boys and 87 girls) discharged with a main diagnosis of infantile autism from any hospital in Sweden before 10 years of age in the period 1987-1994, plus 2,040 matched controls. Conditional logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

The risk of autism was associated with daily smoking in early pregnancy (OR = 1.4; CI = 1.1-1.8), maternal birth outside Europe and North America (OR = 3.0; CI = 1.7-5.2), cesarean delivery (OR = 1.6; CI = 1.1-2.3), being small for gestational age (SGA; OR = 2.1; CI = 1.1-3.9), a 5-minute Apgar score below 7 (OR = 3.2, CI = 1.2-8.2), and congenital malformations (OR = 1.8, CI = 1.1-3.1). No association was found between autism and head circumference, maternal diabetes, being a twin, or season of birth.

CONCLUSIONS

Our findings suggest that intrauterine and neonatal factors related to deviant intrauterine growth or fetal distress are important in the pathogenesis of autism.

Descriptive epidemiology of autism in a California population: who is at risk?

We investigated the association between selected infant and maternal characteristics and autism risk. Children with autism born in California in 1989-1994 were identified through service agency records and compared with the total population of California live births for selected characteristics recorded on the birth certificate. Multivariate models were used to generate adjusted risk estimates. From a live birth population of more than 3.5 million, 4381 children with autism were identified. Increased risks were observed for males, multiple births, and children born to black mothers. Risk increased as maternal age and maternal education increased. Children born to immigrant mothers had similar or decreased risk compared with California-born mothers. Environmental factors associated with these demographic characteristics may interact with genetic vulnerability to increase the risk of autism.

Epidemiology of autism in Singapore: findings of the first autism survey

The report describes the results of a survey conducted on 176 parents of children with autism in Singapore. The ages of the children ranged from 3 to 12 years. The survey focused on the child's background, behaviour problems and skill profile, the home and school situation as well as the linguistic and social background. It was noted that the Singapore population confirms the international distribution regarding a predominance of boys over girls and a low incidence of birth complications. A positive trend noted was the fact that 60% of the children were diagnosed before the age of 3 years. Discussion focuses on possible risk factors and psychosocial adversities for autism such as a high frequency of caregivers who are foreign maids, the use of multiple languages and the high level of punitive educational practices. The possible influence of psychosocial deprivation on child development is discussed.

Prenatal and perinatal risk factors for autism

AIM

To identify pre- and perinatal risk factors for autism.

METHOD

Case control study. We matched names of patients from North Dakota who met DSM criteria for autism, a pervasive developmental disorder, and autistic disorder with their birth certificates. Five matched controls were selected for each case.

RESULTS

Univariate analysis of the 78 cases and 390 controls identified seven risk factors. Logistic modeling to control for confounding produced a five variable model. The model parameters were chi 2 = 36.6 and p < 0.001. The five variables in the model were decreased birth weight, low maternal education, later start of prenatal care, and having a previous termination of pregnancy. Increasing father's age was associated with increased risk of autism.

CONCLUSION

This methodology may provide an inexpensive method for clinics and public health providers to identify risk factors and to identify maternal characteristics of patients with mental illness and developmental disorders.

The screening and diagnosis of autistic spectrum disorders

The Child Neurology Society and American Academy of Neurology recently proposed to formulate Practice Parameters for the Diagnosis and Evaluation of Autism for their memberships. This endeavor was expanded to include representatives from nine professional organizations and four parent organizations, with liaisons from the National Institutes of Health. This document was written by this multidisciplinary Consensus Panel after systematic analysis of over 2,500 relevant scientific articles in the literature. The Panel concluded that appropriate diagnosis of autism requires a dual-level approach: (a) routine developmental surveillance, and (b) diagnosis and evaluation of autism. Specific detailed recommendations for each level have been established in this document, which are intended to improve the rate of early suspicion and diagnosis of, and therefore early intervention for, autism.