Finnish Prenatal Study of Autism and Autism Spectrum Disorders (FIPS-A): Overview and Design

Prevalence of high-risk conditions for severe COVID-19 among Medicaid-enrolled children with autism and mental health diagnoses in the United States

LAY ABSTRACT

Children are at risk of varying severity of illness and even death from COVID-19. We aim to determine whether autistic children or children with mental health conditions have more underlying health conditions that put people at risk of severe illness from COVID-19. We use data from a national sample of Medicaid-enrolled children for the years 2008-2016. These data include children across the 50 states and the District of Columbia. We compare the prevalence of underlying conditions among autistic children and children with mental health condition to that of other children in Medicaid. This study included 888,487 autistic children, 423,397 with any mental health condition (but not autism), and 932,625 children without any of these diagnoses. We found 29.5% of autistic children and 25.2% of children with mental health conditions had an underlying condition with high risk for severe illness from COVID, compared to 14.1% of children without these diagnoses. Autistic children had over twice the odds of having any underlying conditions, when accounting for age, race, sex, and other characteristics. Children with mental health conditions had 70% higher odds of having these underlying conditions. Mitigation measures in schools and other areas could minimize risk of short- and long-term impacts from COVID for autistic and all children.

Novel maternal autoantibodies in autism spectrum disorder: Implications for screening and diagnosis

Introduction

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder for which early recognition is a major challenge. Autoantibodies against fetal brain antigens have been found in the blood of mothers of children with ASD (m-ASD) and can be transferred to the fetus where they can impact neurodevelopment by binding to fetal brain proteins. This study aims to identify novel maternal autoantibodies reactive against human fetal brain antigens, and explore their use as biomarkers for ASD screening and diagnosis.

Methods

A custom-made human fetal brain cDNA phage display library was constructed, and screened for antibody reactivity in m-ASD samples from the Simons Simplex Collection (SSC) of the Simons Foundation Autism Research Initiative (SFARI). Antibody reactivity against 6 identified antigens was determined in plasma samples of 238 m-ASD and 90 mothers with typically developing children (m-TD).

Results

We identified antibodies to 6 novel University Hasselt (UH)-ASD antigens, including three novel m-ASD autoantigens, i.e., ribosomal protein L23 (RPL23), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and calmodulin-regulated spectrin-associated protein 3 (CAMSAP3). Antibody reactivity against a panel of four of these targets was found in 16% of m-ASD samples, compared to 4% in m-TD samples (p = 0.0049).

Discussion

Maternal antibodies against 4 UH-ASD antigens could therefore provide a novel tool to support the diagnosis of ASD in a subset of individuals.

Maternal serum persistent organic pollutant exposure and offspring diagnosed ADHD in a national birth cohort

BACKGROUND

Evidence implicates environmental factors in attention-deficit/hyperactivity disorder (ADHD) risk. Prenatal exposures to polychlorinated biphenyls (PCBs) and the pesticide metabolite p,p'-dichlorodiphenyl dichloroethylene (DDE) have been linked to lower cognitive ability, increased impulsivity, and attention related deficits in the offspring. However, information on the relationship of these exposures to the risk of clinically diagnosed ADHD is limited.

OBJECTIVES

To determine whether prenatal maternal levels of PCBs or DDE are associated with ADHD diagnosis in the offspring.

METHODS

The investigation was conducted in the Finnish Prenatal Study of ADHD (FIPS-ADHD), a case-control study nested in a national birth cohort. Cases were born in 1998 or 1999 and diagnosed with ADHD (ICD-9 314x or ICD-10 F90. x) according to the national Care Register for Health Care. Each case was individually matched to a control on sex, date, and place of birth. PCB congeners (PCB 74, 99, 118, 138, 153, 156, 170, 180, 183, 187) and DDE were quantified from archived prenatal maternal sera from 359 matched case-control pairs using gas chromatography - high triple quadrupole mass spectrometry. Maternal total PCBs were quantified as the sum of concentrations of the measured congeners. Associations with ADHD were examined using conditional logistic regression.

RESULTS

Maternal PCB or DDE levels greater than the 75th percentiles of the control distributions showed no evidence of association with offspring ADHD (PCBs: adjusted odds ratio (aOR) = 1.01, 95% CI = 0.63, 1.60), p = 0.98; DDE: aOR = 1.13, 95% CI = 0.71, 1.81; p = 0.60). Maternal levels of either pollutant dichotomized at the 90th percentile or considered as a continuous variable also did not show evidence for association with offspring ADHD diagnosis.

DISCUSSION

This study did not find evidence for association of maternal prenatal levels of PCBs or DDE with clinical diagnosis of offspring ADHD; however, this does not rule out the possibility of an impact on subclinical phenotypes.

Time trends in treated incidence, sociodemographic risk factors and comorbidities: a Finnish nationwide study on anxiety disorders

BACKGROUND

There has been a lack of research about the time trends and socio-demographic risk factors for children and adolescents who receive treatment for anxiety disorders. This study aimed to fill these gaps in our knowledge by examining a nationwide sample of Finnish children and adolescents diagnosed in specialized healthcare settings.

METHODS

This study comprised national register data of all singleton children born in Finland from 1992-2006 who were diagnosed with anxiety disorders from 1998-2012. The changes in time trends in incidence were studied by dividing the study sample into three cohorts by birth years: 1992-1996, 1997-2001 and 2002-2006, who were followed up until the age of 20, 15 and 10 years, respectively. The 22,388 individuals with anxiety disorders were age and gender matched with 76,139 controls from the general population. Logistic regression was used to examine the socio-demographic risk factors and anxiety disorders in the entire sample. Comorbid disorders were examined in the oldest birth cohort (1992-1996 born).

RESULTS

Comparing the 1992-1996 and 2002-2006 cohorts showed that the cumulative incidence of treated anxiety disorders at the age of 10 increased from 0.3 to 1.2% among females and 0.46 to 1.9% among males. Subjects had higher likelihood for being diagnosed with an anxiety disorder if their mothers had low maternal socio-economic status class at birth (OR 1.53, 95% CI 1.45-1.61) compared to higher SES class, and marital status was single at the time of birth (OR 2.02, 95% CI 1.87-2.17) compared to married or in a relationship. They had lower risk of anxiety disorders diagnosis if born in rural (OR 0.82, 95% CI 0.79-0.86) or semi-urban areas (OR 0.79, 95% CI 0.76-0.82) when compared to urban residence. There was a wide range of psychiatric comorbidities, and unipolar depression was the most common (31.2%).

CONCLUSION

Anxiety disorders diagnosed by specialized Finnish services increased from 1998-2012 in both genders. This could indicate a real increase in overall anxiety disorders or an increase in treatment seeking. The findings on maternal socioeconomic status and single parenting improve the recognition of the environmental risk factors for anxiety disorders among children and adolescents.

A biomarker-based study of prenatal smoking exposure and autism in a Finnish national birth cohort

Maternal exposure to tobacco smoke during pregnancy is a common and persistent exposure linked to adverse neurodevelopmental outcomes in the offspring. However, previous studies provide mixed evidence regarding the relationship between prenatal smoking and offspring autism. This study used cotinine level, a biomarker for nicotine, to investigate the relationship between prenatal smoking and autism. The authors conducted a population-based case-control study nested in a national cohort of all births in Finland from 1987 to 2005. Cases diagnosed with childhood autism (ICD-10/9 code F84.0/299.0) through 2007 were identified using data from linked national registers. Each case was matched with a control on date of birth (±30 days), sex, and place of birth (N = 962 pairs). Maternal serum cotinine levels were prospectively measured in first- to early second-trimester serum samples archived in a national biobank using a quantitative immunoassay. Data were analyzed using conditional logistic regression. Prenatal maternal levels of serum cotinine were not associated with the odds of autism, whether cotinine was classified continuously, by deciles, or using previously defined categories corresponding to probable maternal smoking status. After adjusting for maternal age, paternal age, previous births, and any history of parental psychiatric disorder, the odds ratio for categorical high versus low cotinine, using a 3-level exposure variable, was 0.98 (95% CI = 0.76, 1.26; p = 0.88). In conclusion, this national birth cohort-based study does not provide evidence for an association between maternal cotinine, a biomarker of maternal smoking, and risk of autism. LAY SUMMARY: This study explored whether prenatal exposure to tobacco smoke in mothers is related to the diagnosis of autism in their children, by measuring the levels of cotinine, a biomarker for tobacco exposure, in stored serum samples drawn from mothers during pregnancy. The levels of cotinine in the mothers of children diagnosed with autism were similar to those in the mothers of control children of similar age and gender distribution.

Risk for Premature Mortality and Intentional Self-harm in Autism Spectrum Disorders

To examine the risk for premature mortality and intentional self-harm in autism spectrum disorders (ASD). Based on a national birth cohort. Children born in 1987-2005, diagnosed with ASD by 2007 (n = 4695) were matched with four non-ASD subjects (n = 18,450) and followed until 2015 for mortality and intentional self-harm. The risk among ASD subjects was elevated only for natural cause of death. The risk for intentional self-harm was increased in the unadjusted analyses, but decreased to non-significant after adjusting for comorbid psychiatric disorders. ASD subjects are at increased risk for premature mortality due to natural causes of death. While ASD subjects die of suicide and present with more self-harm, the association is explained by comorbid psychiatric disorders.

Perinatal risk factors and reactive attachment disorder: A nationwide population-based study

AIM

To examine the association between several perinatal and obstetric risk factors and reactive attachment disorder in children diagnosed in specialised services.

METHODS

In this nested case-control study, 614 cases with reactive attachment disorder and 2423 controls matched with age and sex were identified from Finnish national registers. Conditional logistic regression was used to examine the association between a number of perinatal risk factors and reactive attachment disorder.

RESULTS

In the adjusted analysis, a low birthweight of <2500 g was associated with an increased odds of reactive attachment disorder, with an odds ratio (OR) of 1.96 and 95% confidence interval (CI) of 1.17, 3.30 and a birthweight of 4000-4499 grams was associated with decreased odds OR 0.49 (95% CI 0.31, 0.75). The odds for being diagnosed with reactive attachment disorder increased with a gestational age of <32 weeks OR 3.72 (95% CI 1.52, 9.10), induced labour OR 1.34 (95% CI 1.03, 1.75) and monitoring in a neonatal intensive care unit (NICU) OR 1.67 (95% CI 1.09, 2.55).

CONCLUSION

We found associations between low birthweight, preterm birth, NICU admission and reactive attachment disorder. The findings add to the current literature on the understanding of the development of reactive attachment disorder in children.

The Finnish psychiatric birth cohort consortium (PSYCOHORTS) - content, plans and perspectives

Background: Psychiatric disorders tend to be developmental, and longitudinal settings are required to examine predictors of psychiatric phenomena. Replicating and combining data and results from different birth cohorts, which are a source of reliable data, can make research even more valuable. The Finnish Psychiatric Birth Cohort Consortium (PSYCOHORTS) project combines birth cohorts in Finland. Aim: The aim of this paper is to introduce content, plans and perspectives of the PSYCOHORTS project that brings together researchers from Finland. In addition, we illustrate an example of data harmonization using available data on causes of death. Content: PSYCOHORTS includes eight Finnish birth cohorts. The project has several plans: to harmonize different data from birth cohorts, to incorporate biobanks into psychiatric birth cohort research, to apply multigenerational perspectives, to integrate longitudinal patterns of marginalization and inequality in mental health, and to utilize data in health economics research. Data on causes of death, originally obtained from Finnish Cause of Death register, were harmonized across the six birth cohorts using SAS macro facility. Results: Harmonization of the cause of death data resulted in a total of 21,993 observations from 1965 to 2015. For example, the percentage of deaths due to suicide and the sequelae of intentional self-harm was 14% and alcohol-related diseases, including accidental poisoning by alcohol, was 13%. Conclusions: PSYCOHORTS lays the foundation for complex examinations of psychiatric disorders that is based on compatible datasets, use of biobanks and multigenerational approach to risk factors, and extensive data on marginalization and inequality.

Proband and Familial Autoimmune Diseases Are Associated With Proband Diagnosis of Autism Spectrum Disorders

OBJECTIVE

There is evidence that parental autoimmune diseases (ADs) are associated with autism spectrum disorders (ASD) in offspring. The association between offspring ASD and ADs diagnosed in siblings and probands remains less clear. We examined whether proband and familial diagnoses of ADs were associated with increased odds of ASD in probands.

METHOD

The study is based on a nested case-control design that used data from a large national birth cohort (N = 1.2 million) in Finland. There were 4,600 cases of ASD and controls matched 1:4 on date of birth, sex, and residence. Data were accessed from national medical, birth, and central registries.

RESULTS

Probands had a statistically significant increase in odds of ASD when they (adjusted odds ratio [OR] = 1.2), their mother (adjusted OR = 1.1), or their sibling (adjusted OR = 1.2) were diagnosed with an AD. With regard to specific ADs, we found a statistically significant increase in odds of ASD in probands diagnosed with autoimmune thyroiditis (adjusted OR = 2.7). Further analyses considering ADs by body system yielded a statistically significant increase in odds of ASD in probands with ADs associated with the central/peripheral nervous (adjusted OR = 4.8) and skin/mucous membrane (adjusted OR = 1.3) systems. Probands of mothers diagnosed with ear/eye (adjusted OR = 1.6) or respiratory (adjusted OR = 1.4) ADs, or siblings diagnosed with skin/mucous membrane ADs (adjusted OR = 1.3) also had increased odds of ASD.

CONCLUSION

The findings suggest that there may be common pathogenic, developmental mechanisms related to autoimmunity that are associated with the etiology of ASD.

Parental Risk Factors among Children with Reactive Attachment Disorder Referred to Specialized Services: A Nationwide Population-Based Study

This nationwide population-based register study examined the family and parental risk factors associated with offspring reactive attachment disorder (RAD). We identified 614 children diagnosed with RAD from the Finnish Care Register for Health Care and each case was matched with four controls. Univariate and multivariate models examined the associations between risk factors and RAD. In the multivariate model, offspring RAD was associated with only mother, only father and both parents having psychiatric diagnoses. Increased odds were observed for maternal smoking during pregnancy, single motherhood and paternal age ≥ 45 years. This study provides information on several parental adversities and offspring RAD that have important implications for public health, when planning early prevention and interventions in infant mental health.

Association of Maternal Insecticide Levels With Autism in Offspring From a National Birth Cohort

OBJECTIVE

Autism is a complex neurodevelopmental disorder with a largely unknown etiology. To date, few studies have investigated prenatal exposure to toxins and risk of autism by using maternal biomarkers of exposure. Persistent organic pollutants are lipophilic halogenated organic compounds and include the insecticide dichlorodiphenyltrichloroethane (DDT), as well as its metabolite p,p'-dichlorodiphenyl dichloroethylene (p,p'-DDE), and polychlorinated biphenyls (PCBs). The objective of this study was to test whether elevated maternal levels of persistent organic pollutants are associated with autism among offspring.

METHOD

The investigation was derived from the Finnish Prenatal Study of Autism, a national birth cohort study based on a nested case-control design. Cases of autism among children born between 1987 and 2005 were ascertained by national registry linkages. In cases of childhood autism and matched control subjects (778 matched case-control pairs), maternal serum specimens from early pregnancy were assayed for levels of p,p'-DDE and total levels of PCBs.

RESULTS

The odds of autism among offspring were significantly increased with maternal p,p'-DDE levels that were in the highest 75th percentile, with adjustment for maternal age, parity, and history of psychiatric disorders (odds ratio=1.32, 95% CI=1.02, 1.71). The odds of autism with intellectual disability were increased by greater than twofold with maternal p,p'-DDE levels above this threshold (odds ratio=2.21, 95% CI=1.32, 3.69). There was no association between total levels of maternal PCBs and autism.

CONCLUSIONS

These findings provide the first biomarker-based evidence that maternal exposure to insecticides is associated with autism among offspring. Although further research is necessary to replicate this finding, this study has implications for the prevention of autism and may provide a better understanding of its pathogenesis.

Parental psychopathology and offspring attention-deficit/hyperactivity disorder in a nationwide sample

OBJECTIVE

To study the associations between a wide range of parental psychiatric disorders and offspring attention-deficit/hyperactivity disorder (ADHD).

METHOD

This study is based on a nested case-control design. The association between parental registered psychiatric diagnoses and offspring ADHD was examined adjusting for socioeconomic and prenatal factors. Data was linked from Finnish nationwide registers. The cases (n = 10,409) were all the children born between years 1991 and 2005 in Finland and diagnosed with ADHD by the end of 2011. Four controls without ADHD (n = 39,124) were matched for every case by sex, age and place of birth. Main outcomes were adjusted odds ratio (aOR) for parental diagnosis of cases vs controls. Analyses were further stratified by sex. Disorders diagnosed before and after birth were analyzed separately.

RESULTS

The odds ratio for ADHD increased when only mother (aOR 2.2, 95% CI 2.0-2.3), only father (aOR 1.7, 95% CI 1.6-1.8) and both parents (aOR 3.6, 95% CI 3.3-4.0) were diagnosed. Maternal diagnosis showed stronger association than paternal. The weight of association between several parental disorders and offspring ADHD were similar. Maternal psychopathology overall showed stronger associations with girls than boys with ADHD. The diagnoses registered after birth did not show stronger association than the diagnoses registered before.

CONCLUSIONS

Maternal psychopathology showing stronger association than paternal implies that environmental factors or their interaction with genetic factors partly mediates the risk of parental psychopathology. Similar associations between several maternal psychiatric disorders and offspring ADHD points towards the need for investigating some common mother-related risk factors.

Prenatal toxoplasmosis antibody and childhood autism

There is evidence that some maternal infections during the prenatal period are associated with neurodevelopmental disorders, such as childhood autism. However, the association between autism and Toxoplasma gondii (T. gondii), an intracellular parasite, remains unclear. The authors examined whether serologically confirmed maternal antibodies to T. gondii are associated with odds of childhood autism in offspring. The study is based on a nested case-control design of a large national birth cohort (N = 1.2 million) and the national psychiatric registries in Finland. There were 874 cases of childhood autism and controls matched 1:1 on date of birth, sex, birthplace and residence in Finland. Maternal sera were prospectively assayed from a national biobank for T. gondii IgM and IgG antibodies; IgG avidity analyses were also performed. High maternal T. gondii IgM antibody was associated with a significantly decreased odds of childhood autism. Low maternal T. gondii IgG antibody was associated with increased offspring odds of autism. In women with high T. gondii IgM antibodies, the IgG avidity was high for both cases and controls, with the exception of three controls. The findings suggest that the relationship between maternal T. gondii antibodies and odds of childhood autism may be related to the immune response to this pathogen or the overall activation of the immune system. Autism Res 2017, 10: 769-777. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.

Register-based study of the incidence, comorbidities and demographics of obsessive-compulsive disorder in specialist healthcare

BACKGROUND

Incidence of obsessive-compulsive disorder (OCD) has been suspected to increase but nationwide epidemiological studies are limited. This study aims to examine sex-specific incidence time trends and characterize psychiatric and neurodevelopmental comorbidities and sociodemographic risk factors of OCD in specialist healthcare in Finland.

METHODS

A nationwide register-based study using data from four Finnish registers identified 3372 OCD cases and 13,372 matched controls (1:4). Cumulative incidence in subjects born between 1987 and 2001 was estimated at ages of 10, 15, 20 and 23 years. Conditional logistic regression was used to examine the sociodemographic factors.

RESULTS

The cumulative incidence of OCD was 0.4% by age 23. Incidence by age 15 among three cohorts increased from 12.4 to 23.7 /10000 live born males and 8.5 to 28.0 /10000 live born females. 73% of the sample had a comorbid condition. Males were significantly more comorbid with psychotic and developmental disorders; females were more comorbid with depressive and anxiety disorders (p <0.001). Higher maternal SES was associated with an increased risk of OCD (OR 1.4; 95% CI 1.1-1.6).

CONCLUSIONS

These findings suggest that incidence of treated OCD in specialist healthcare has increased. The reason may be increased awareness and rate of referrals but a true increase cannot be ruled out. Further research on risk factors of OCD is warranted.

Contribution of maternal hypertension to autism etiology in a murine model; cerebellar gene expression

Aim: To study the contribution of maternal hypertension to autism spectrum disorders’ (ASD) phenotype, and gene expression, in a murine model. Materials & methods: To examine the effects of maternal hypertension, we used a well-described transgenic mouse model lacking functional endothelial nitric oxide synthase (eNOS or NOS3). Behavioral testing was performed on male offspring between 8 and 10 weeks of age. Cerebella underwent shotgun transcriptome RNA sequencing. Differentially expressed genes were examined for Gene Ontology enrichment. 2-way-RM-ANOVA, 1-way-ANOVA and Student's t-test were used for statistical analysis. Results & conclusion: Our findings revealed that a deficit in social behavior, the hallmark of ASD, is differentially present in offspring born to hypertensive mothers. Novel ASD-related genes were differentially expressed in the cerebellum, implicating its possible role in ASD etiology. Condensation: Altered uterine environment resulting from maternal hypertension contributes to ASD phenotype, and modifies expression of novel ASD-related genes in cerebella of eNOS heterozygous offspring.

Demographic Characteristics and Psychiatric Comorbidity of Children and Adolescents Diagnosed with ADHD in Specialized Healthcare

Recent studies have shown an increasing incidence of attention-deficit/hyperactivity disorder (ADHD) among children diagnosed in specialized services. This study aims to describe children with ADHD in Finnish specialized healthcare by reporting the demographic characteristics, time trends in diagnosis, psychiatric comorbidity, and the validity of register-based diagnoses. All the singletons born in Finland between 1991 and 2005 and diagnosed with ADHD by 2011 were identified and their psychiatric comorbidity data was obtained from the Finnish Hospital Discharge Register (FHDR). Parents of 69 patients were interviewed via telephone for a diagnostic validation. A total of 10,409 children were identified with ADHD, with a male: female ratio of 5.3:1 and a psychiatric comorbidity rate of 76.7 %. Of the validation sample 88 % met the diagnostic criteria of ADHD for DSM-IV. There is an increasing trend of ADHD diagnosis among both males and females. Psychiatric comorbidity is common and includes a wide range of disorders among children with ADHD. There was an increase of ADHD diagnoses especially among boys. More attention is needed to detect ADHD among girls in health services. Diagnoses in the FHDR show diagnostic validity and their sociodemographic patterns are in line with previous studies.

Parental migration and Asperger's syndrome

Parental immigration has been suggested as a possible risk factor for autism spectrum disorders (ASD), but findings have been inconsistent. Very few studies have focused specifically on Asperger's syndrome. The aim of this study was to examine the association between maternal and paternal immigration and the diagnosis of Asperger's syndrome in offspring. The study was a nested case-control study based on a national birth cohort in Finland. Children born in 1987-2005 and diagnosed with Asperger's syndrome by the year 2007 were identified from the Finnish Hospital Discharge Register (N = 1,783). Four matched controls for each case were selected from the Finnish Medical Birth Register (N = 7,106). Information on maternal and paternal country of birth and mother tongue was collected from the Finnish Central Population Register. The study showed that children whose parents are both immigrants have a significantly lower likelihood of being diagnosed with Asperger's syndrome than those with two Finnish parents [adjusted odds ratio (aOR) 0.2, 95 % confidence interval (CI) 0.1-0.4]. No significant associations were found between having only one immigrant parent and the diagnosis of Asperger's syndrome. A regional analysis showed a significantly decreased likelihood of the diagnosis of Asperger's syndrome in children whose mother (aOR 0.1, 95 % CI 0.01-0.5) or father (aOR 0.2, 95 % CI 0.05-0.5) was born in Sub-Saharan Africa. The findings may help in identifying risk factors for different ASD subtypes. On the other hand, they might reflect service use of immigrant families in Finland.

Autism with intellectual disability related to dynamics of head circumference growth during early infancy

BACKGROUND

It is not yet definitively known whether dynamic features of head circumference growth are associated with autism. To address this issue, we carried out a nested matched case-control study using data from national well baby clinics in Finland; autism cases were identified from the Finnish Hospital and Outpatient Discharge Registry.

METHODS

A nonparametric Bayesian method was used to construct growth velocity trajectories between birth and 2 years of age in autism cases and matched control subjects (n = 468 in main analyses, 1:1 matched control subjects). Estimates of odds ratios for autism risk in relation to the growth velocities were obtained using conditional logistic regression.

RESULTS

Growth velocity of head circumference at 3 months of age, adjusting for gestational age at birth and maternal age, is significantly associated with autism (p = .014); the finding was observed in subjects with comorbid intellectual disability (ID) (p = .025) but not in those without ID (p = .15). Height growth velocity among subjects with autism and without ID is significantly associated with autism at 6 months (p = .007), and weight growth velocity at 18 months without ID (p = .02) and 24 months without ID (p = .042) and with ID (p = .037).

CONCLUSIONS

Acceleration in head circumference growth is associated with autism with comorbid ID at 3 months but not subsequently. This association is unrelated to acceleration in height and weight, which are not strongly associated with autism until after 6 months.

Maternal thyroid autoantibody and elevated risk of autism in a national birth cohort

OBJECTIVE

Autoimmune disruption may contribute to risk for autism; however, since previous studies relied upon clinical diagnoses, exposure misclassification and recall bias are limitations. Thyroid peroxidase antibody (TPO-Ab) is an autoantibody involved in autoimmune thyroiditis. We aimed to test the a priori hypothesis that positivity to maternal serum TPO-Ab (TPO-Ab+) (defined as >156 IU/ml) during pregnancy is related to childhood autism.

METHOD

The study was based on a nested case-control design of the Finnish Prenatal Study of Autism (FiPS-A), a national birth cohort that includes prospectively drawn archived maternal serum specimens from virtually the entire pregnant population of Finland beginning in 1983. Cases of childhood autism (ICD-10F84.0) born from 1987 to 2005 were ascertained by performing linkages between national birth and inpatient/outpatient registries. All diagnosed cases in Finland over the birth years, and comparison subjects without ASD or severe/profound intellectual disability were matched 1:1 on date of birth, sex, birthplace, and residence in Finland. Maternal serum specimens were assayed in 967 matched case-control pairs for TPO-Ab by a chemiluminescent microparticle immunoassay blind to case/control status. Data were analyzed by conditional logistic regression for matched sets.

RESULTS

The prevalence of maternal TPO-Ab+ was significantly increased in pregnancies giving rise to autism cases (6.15%) compared to controls (3.54%). The odds of autism were increased by nearly 80% among offspring of mothers who were TPO-Ab+ during pregnancy (OR=1.78, 95% CI=1.16-2.75, p=0.009), compared to mothers negative for this autoantibody. There was also a significant relationship between maternal TPO-Ab defined as a continuous variable and odds of autism (OR=1.09, 95% CI=1.01, 1.17, p=0.02). Measures of maternal thyroid hormones did not differ between groups.

CONCLUSIONS

These findings provide the first biomarker-based evidence that a class of known maternal autoimmune disorders is related to autism in offspring.

The association between congenital anomalies and autism spectrum disorders in a Finnish national birth cohort

AIM

The first aim of this study was to evaluate the association between different subgroups of autism spectrum disorders (ASDs) (childhood autism, Asperger syndrome, and pervasive developmental disorder/pervasive developmental disorder - not otherwise specified [PDD/PDD-NOS]) and congenital anomalies. Second, we assessed the association among intellectually disabled children with ASDs in the subgroups of childhood autism and PDD/PDD-NOS.

METHOD

Nationwide population-based register data for children with a diagnosis of ASD (n=4449; 3548 males, 901 females) were collected during years 1987-2000 from the Finnish Hospital Discharge Register. Data on congenital anomalies were derived from the National Register of Congenital Malformations. Conditional logistic regression models were used as a statistical method. The association between ASD subgroups and congenital anomalies was stratified by the presence or absence of intellectual disability.

RESULTS

Congenital anomalies occurred more frequently in all subgroups of ASD than in comparison participants (adjusted odds ratio [OR] for major congenital anomalies 1.8, 95% confidence interval [CI] 1.5-2.2, p<0.001). The association between congenital anomalies and childhood autism (OR 2.4, 95% CI 1.6-3.6, p<0.001) and between congenital anomalies and PDD/PDD-NOS (OR 3.7, 95% CI 2.4-5.7, p<0.001) among children with an intellectual disability was strong but remained significant also without intellectual disability (childhood autism: OR 1.7, 95% CI 1.3-2.3, p<0.001; PDD/PDD-NOS: OR 2.3, 95% CI 1.9-2.8, p<0.001).

INTERPRETATION

The results suggest a significant association between ASDs and congenital anomalies regardless of the ASD subgroup. The association between childhood autism and PDD/PDD-NOS and congenital anomalies is stronger among children with intellectual disability is stronger than among those without intellectual disability. These results may have relevance in examining early risk factors in autism during fetal neurodevelopment.

Maternal socio-economic status based on occupation and autism spectrum disorders: a national case-control study

BACKGROUND

The association between parental socio-economic status (SES) and autism spectrum disorders (ASD) has been studied in several countries, but the results have been contradictory.

AIMS

The aim of this study was to examine the association between maternal SES and subtypes of ASD in Finland.

METHODS

A national case-control study was conducted. Children born in 1991-2005 and diagnosed with ASD by the year 2007 were identified from the Finnish Hospital Discharge Register (FHDR). Their matched controls were selected from the Finnish Medical Birth Register (FMBR). There were 3468 cases and 13,868 controls. The information on maternal SES was collected from the FMBR and categorized into upper white-collar workers (referent), lower white-collar workers, blue-collar workers and "others", consisting of students, housewives and other groups with unknown SES. The statistical test used was conditional logistic regression.

RESULTS

The likelihood of ASD was increased among offspring of mothers who belong to the group "others" (adjusted OR = 1.2, 95% CI 1.009-1.3). The likelihood of Asperger's syndrome was decreased among offspring of lower white-collar workers (adjusted OR = 0.8, 95% CI 0.6-0.9) and blue-collar workers (adjusted OR = 0.6, 95% CI 0.5-0.7). The likelihood of pervasive developmental disorder not otherwise specified (PDD-NOS) was increased among offspring of blue-collar workers (adjusted OR = 1.5, 1.2-1.9) and "others" (adjusted OR = 1.3, 1.1-1.7). No association was found between maternal SES and childhood autism.

CONCLUSIONS

The association between maternal SES and ASD differs by ASD subtype. Socio-economic groups might differ from each other by risk factors for ASD subtypes or by their service use.

Environmental chemical exposures and autism spectrum disorders: a review of the epidemiological evidence

In the past decade, the number of epidemiological publications addressing environmental chemical exposures and autism has grown tremendously. These studies are important because it is now understood that environmental factors play a larger role in causing autism than previously thought and because they address modifiable risk factors that may open up avenues for the primary prevention of the disability associated with autism. In this review, we covered studies of autism and estimates of exposure to tobacco, air pollutants, volatile organic compounds and solvents, metals (from air, occupation, diet, dental amalgams, and thimerosal-containing vaccines), pesticides, and organic endocrine-disrupting compounds such as flame retardants, non-stick chemicals, phthalates, and bisphenol A. We included studies that had individual-level data on autism, exposure measures pertaining to pregnancy or the 1st year of life, valid comparison groups, control for confounders, and adequate sample sizes. Despite the inherent error in the measurement of many of these environmental exposures, which is likely to attenuate observed associations, some environmental exposures showed associations with autism, especially traffic-related air pollutants, some metals, and several pesticides, with suggestive trends for some volatile organic compounds (e.g., methylene chloride, trichloroethylene, and styrene) and phthalates. Whether any of these play a causal role requires further study. Given the limited scope of these publications, other environmental chemicals cannot be ruled out, but have not yet been adequately studied. Future research that addresses these and additional environmental chemicals, including their most common routes of exposures, with accurate exposure measurement pertaining to several developmental windows, is essential to guide efforts for the prevention of the neurodevelopmental damage that manifests in autism symptoms.

Increased risk of autism spectrum disorders at short and long interpregnancy intervals in Finland

OBJECTIVE

Both short and long interpregnancy intervals (IPI) are believed to present possible adverse conditions for fetal development. Short IPI has recently been associated with increased risk of autism, but whether long IPI increases risk for autism spectrum disorders (ASD) has not been thoroughly investigated. We investigated the association between short and long IPI in a Finnish population-based study.

METHOD

This study was conducted in the Finnish Prenatal Study of Autism, which is based in a national birth cohort. Children born in Finland in 1987 to 2005 and diagnosed with ASD by 2007 were identified through the Finnish Hospital Discharge Register. A total of 2,208 non-firstborn patients with ASD and 5,163 matched controls identified from the Finnish Medical Birth Register were included in the primary analysis. The association between IPI and ASD was determined using conditional logistic regression and adjusted for potential confounders.

RESULTS

Relative to births with an IPI of 24 to 59 months, those with the shortest IPI (<12 months) had an increased risk of ASD (odds ratio [OR] = 1.50, 95% CI = 1.28, 1.74) in confounder-adjusted models, whereas the ORs for longer IPI births (60-119 months and ≥120 months) were 1.28 (95% CI = 1.08, 1.52) and 1.44 (95% CI = 1.12, 1.85), respectively.

CONCLUSION

This study provides evidence that risk of ASD is increased at long as well as short IPI.

The incidence of diagnosed autism spectrum disorders in Finland

BACKGROUND

Previous reports indicate an increase in incidence of autism spectrum disorders (ASD).

AIMS

First, to assess the incidence of diagnosed ASD in children born between 1996 and 1998, based on nationwide inpatient and outpatient register information. Second, to investigate the incidence rate over time of diagnosed ASD and specifically childhood autism, Asperger's syndrome and pervasive developmental disorder (PDD-NOS) in children born between 1987 and 1998.

METHODS

This is population-based cohort study with children born in Finland between 1 January 1987 and 31 December 2005; a total of more than 1.2 million children. Children were identified in the Finnish Hospital Discharge Register, and the reported diagnoses were based on the International Statistical Classification of Diseases (ICD-10, ICD-9).

RESULTS

The annual incidence rate of diagnosed ASD based on inpatient and outpatient register data was 53.7 per 10,000 (95% CI 50.4-57.2). Incidence was 82.6 per 10,000 in boys and 23.6 per 10,000 in girls, yielding a sex ratio (boys:girls) of 3.5:1. We report an eightfold increase in the incidence rates in children of diagnosed ASD and specifically in childhood autism, Asperger's syndrome and PDD-NOS and born between 1987 and 1992 based on inpatient register information.

CONCLUSIONS

Increased awareness of ASD, more precise diagnostic criteria and changes in practice for diagnosing autism may have had a substantial effect on the increased incidence of inpatient treated ASD cases from 1987 to 1992. Between 1992 and 1998, the incidence rate based on inpatient and outpatient service use remained rather stable.

Parental age and the risk of bipolar disorders

OBJECTIVES

Studies on the association between parental age and bipolar disorder (BPD) are scarce and with inconsistent findings. The aim of this study was to examine the association of parental age and age difference between parents with risk of BPD in offspring.

METHODS

This nested case-control study identified 1,861 cases of individuals with BPD born in Finland during 1983-1998 and diagnosed by the end of 2008, and 3,643 sex- and date of birth-matched controls from nationwide population-based registers. Conditional logistic regression was used to examine the association adjusting for potential confounding due to age of the other parent, parental psychiatric history, educational level, and place of birth.

RESULTS

A U-shaped association of unadjusted odds ratios (ORs) for BPD risk was seen in different paternal age categories, with the odds increasing at both ends of the age spectrum. In the adjusted analyses, offspring of fathers aged ≥ 50 years had a 2.8-fold increased odds [OR = 2.84, 95% confidence interval (CI): 1.32-6.12] of BPD as compared to those with fathers aged 30-34 years. The odds were increased 1.3-fold (OR = 1.35, CI: 1.06-1.72) in fathers aged 20-24 years. No significant association was found between maternal age and BPD in the adjusted analyses. Age difference between parents was not associated with BPD.

CONCLUSIONS

The increased risk of BPD in offspring of the youngest and oldest fathers in the study suggests the involvement of different biological and psychosocial factors at the two ends of the paternal age spectrum. These findings may be significant in the context of advancing parental age in recent times.

Finnish Prenatal Study of Bipolar Disorders (FIPS-B): overview, design and description of the sample

BACKGROUND

Bipolar disorders (BPD) are chronic mental illnesses, the development of which involves genetic factors and environmental influences.

AIMS

The aim of this paper is to provide an overall description of the Finnish Prenatal Study of Bipolar Disorders (FIPS-B), including the study design, national registers and linkage of the registers.

METHODS

FIPS-B is a population-based prenatal epidemiological study of BPD with a nested case-control study design using several national registers. The registers used are: the Finnish Medical Birth Register (FMBR), the Finnish Hospital Discharge Register (FHDR), the Population Central Register and the Finnish Maternity Cohort (FMC), which are linked using the unique personal identity code (PIC). FIPS-B includes all children born from January 1, 1983 to December 31, 1998 and diagnosed with BPD in Finland by December 31, 2008.

RESULTS

The total number of cases included in the FIPS-B is 1887. The age at first diagnosis ranged from 4 to 25 years. Half (50.4%) of the cases utilized only outpatient services, 12.7% only inpatient services and the rest (36.9%) utilized both services. Offspring of mothers with the lowest educational level had an increased odds of BPD (OR = 1.46, 95% CI 1.13-1.88). The cumulative incidence of BPD in the population aged 25 years or younger was 11.6/10,000 in 2008.

CONCLUSIONS

FIPS-B has all the strengths of a register-based prenatal epidemiological study, along with the availability of maternal biomarkers, enabling it to examine several prenatal, perinatal and familial risk factors for BPD.

Increasing prevalence, changes in diagnostic criteria, and nutritional risk factors for autism spectrum disorders

The frequency of autism spectrum disorders (ASD) diagnoses has been increasing for decades, but researchers cannot agree on whether the trend is a result of increased awareness, improved detection, expanding definition, or an actual increase in incidence or a combination of these factors. Though both genetic and multiple environmental risk factors have been studied extensively, many potentially modifiable risk factors including nutritional and immune function related risk factors such as vitamin D, folic acid, and metabolic syndrome have not received sufficient attention. Several recent studies have put forward hypotheses to explain the mechanism of association between both folic acid and vitamin D and autism. A continuous rise in the prevalence of autism in the USA has coincided with a significant enhancement of maternal folate status with FDA mandated folic acid fortification of certain foods starting in 1998. There is also a growing body of research that suggests that vitamin D status either in utero or early in life may be a risk for autism. In this communication, controversies regarding increase in estimate of prevalence, implications of changes in definition, and possible association between some modifiable nutritional risk factors such as folic acid and vitamin D and ASD will be discussed.

Elevated maternal C-reactive protein and autism in a national birth cohort

Autism is a complex neuropsychiatric syndrome with a largely unknown etiology. Inflammation during pregnancy may represent a common pathway by which infections and other insults increase risk for the disorder. Hence, we investigated the association between early gestational C-reactive protein (CRP), an established inflammatory biomarker, prospectively assayed in maternal sera, and childhood autism in a large national birth cohort with an extensive serum biobank. Other strengths of the cohort included nearly complete ascertainment of pregnancies in Finland (N=1.2 million) over the study period and national psychiatric registries consisting of virtually all treated autism cases in the population. Increasing maternal CRP levels, classified as a continuous variable, were significantly associated with autism in offspring. For maternal CRP levels in the highest quintile, compared with the lowest quintile, there was a significant, 43% elevated risk. This finding suggests that maternal inflammation may have a significant role in autism, with possible implications for identifying preventive strategies and pathogenic mechanisms in autism and other neurodevelopmental disorders.

Obstetric risk factors and autism spectrum disorders in Finland

OBJECTIVE

To examine the relationship between obstetric risk factors and childhood autism, Asperger syndrome, and other pervasive developmental disorders (PDDs).

STUDY DESIGN

Registry-based case-control study from all singleton births in Finland from 1990-2005. Cases with childhood autism, Asperger syndrome, or PDD (n = 4713) were identified from the Finnish Hospital Discharge Register. Each case was matched to 4 controls on sex, date of birth, and place of birth. Information on obstetric risk factors was from the Finnish Medical Birth Register. Conditional logistic regression models were used for statistical analyses.

RESULTS

When adjusted with confounders, childhood autism was associated with maternal high blood pressure (OR 1.49, 95% CI 1.1-2.1, P = .018), Apgar scores less than 7 (1 minute, OR 1.46, 95% CI 1.1-2.0, P = .021), and neonatal treatment with monitoring (OR 1.40, 95% CI 1.02-1.9, P = .038). PDD was associated with induced labor (OR 1.25 95% CI 1.1-1.5, P = .007), planned cesarean delivery (OR 1.34, 95% CI 1.1-1.7, P = .009), 1-minute Apgar scores 7-8 ( OR 1.22, 95% CI 1.1-1.4, P = .008) and less than 7 (OR 1.34, 95% CI 1.03-1.8, P = .032), and neonatal intensive care unit treatment (OR 1.52, 95% CI 1.2-2.0, P = .003). Asperger syndrome was associated only with 1-minute Apgar scores 7-8 (OR 1.19, 95% CI 1.03-1.4, P = .018).

CONCLUSIONS

Low Apgar scores as well as conditions requiring neonatal special follow-up are important risk factors for childhood autism and PDD. These findings suggest that fetal distress is a potential risk factor for these disorders, but not for Asperger syndrome.

Variation by diagnostic subtype in risk for autism spectrum disorders associated with maternal parity among Finnish births

BACKGROUND

Associations between maternal parity and outcomes in offspring may provide evidence for involvement of prenatal exposures. The objective of this study was to determine whether risk for autism spectrum disorders (ASD) is associated with maternal parity.

METHODS

Diagnoses of childhood autism, Asperger syndrome, and pervasive developmental disorder, not otherwise specified (PDD-NOS) were examined separately and as a group. The study was conducted in the Finnish Prenatal Study of Autism, which is based in a national birth cohort. Children born in Finland in 1987-2005 and diagnosed with ASD by 2007 were identified through the Finnish Hospital Discharge Register. Four matched controls were selected for each case using the Finnish Medical Birth Register. The association between parity and each ASD was determined using conditional logistic regression and adjusted for number of children in the sibship and other potential confounders.

RESULTS

ASDs combined showed a pattern of decreasing risk with increasing parity (odds ratio OR for fourth or greater vs. first-born children, 0.43 [95% confidence interval (CI): 0.35, 0.51]). For childhood autism, an adjusted OR of 1.51 [95% CI 1.27, 1.81] was observed for second vs. first-born children. Associations for Asperger syndrome and PDD-NOS were consistent with those for all ASDs.

CONCLUSIONS

Differences in patterns of association between maternal parity and ASD subtypes may indicate varying contributions of specific environmental factors to risk; however, differences in diagnosis or in treatment seeking for childhood behavioural problems cannot be ruled out, particularly for higher functioning cases.

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.

The risk of childhood autism among second-generation migrants in Finland: a case-control study

Background

Studying second-generation immigrants can help in identifying genetic or environmental risk factors for childhood autism. Most previous studies have focused on maternal region of birth and showed inconsistent results. No previous study has been conducted in Finland.

Methods

The study was a nested case–control study based on a national birth cohort. Children born in 1987–2005 and diagnosed with childhood autism by the year 2007 were identified from the Finnish Hospital Discharge Register. Controls were selected from the Finnish Medical Birth Register. Information on maternal and paternal country of birth and mother tongue was collected from the Finnish Central Population Register. There were 1132 cases and 4515 matched controls. The statistical test used was conditional logistic regression analysis.

Results

Compared with children with two Finnish parents, the risk of childhood autism was increased for those whose parents are both immigrants (adjusted odds ratio [aOR] 1.8, 95% confidence interval [CI] 1.2–2.7) and for those with only an immigrant mother (aOR 1.8, 95% CI 1.2–2.7), but not for those with only an immigrant father. The risk was increased for those with a mother born in the former Soviet Union or Yugoslavia and for those with a mother or a father born in Asia. Specific parental countries of birth associated with an increased risk were the former Soviet Union, the former Yugoslavia and Vietnam.

Conclusions

In Finland, children who are born to immigrant mothers with or without an immigrant partner, have an increased risk of childhood autism. The risk varies with immigrant parents’ region of birth. The findings may help in identifying possible risk factors, which can be examined in future studies.

Maternal serum persistent organic pollutants in the Finnish Prenatal Study of Autism: A pilot study

Recent research emphasizes the contribution of environmental as well as genetic factors to the etiology of autism but studies testing associations between chemical exposures and autism have been limited. Prenatal exposure to persistent organic pollutants (POPs) has previously been associated with decrements in cognitive and developmental performance. We conducted a pilot study in the Finnish Prenatal Study of Autism (FiPS-A). Seventy-five cases with autism and 75 controls matched on sex, birth year, urbanization and maternal age were sampled from first-born children in the Finnish Maternity Cohort, which includes over 1million births. The study sample included births occurring from 1991 to 2000. Subjects were followed up for autism through 2007. DDT, DDE, PCB-118, PCB-138, PCB-153, PCB-156, PCB-170, PCB-180, hexachlorobenzene, and BDE-47 were measured in archived maternal serum samples taken during pregnancy using gas chromatography-high resolution mass spectrometry. Correlations between pollutant measures were assessed and mechanistically-related weighting schemes for summarizing PCB levels were compared. Case and control differences were assessed using graphical and statistical methods. All analytes, with the exception of DDT and BDE-47, were detected above the limit of quantification in all samples. The correlation between levels of individual PCB congeners and weighted summary measures was high (0.71-1.00). Paired t-tests revealed no significant differences between cases and controls for log-transformed mean values of any analyte; however, in an adjusted model the odds ratios for autism were 1.91 (p=0.29) and 1.79 (p=0.36) respectively, for subjects with total PCBs and DDE above the 90th percentile of control values. Levels of prenatal PCB exposure in FIPS-A were similar to the levels which previously correlated with poorer neurodevelopmental measures in other populations. Further study in a larger sample will be required to fully determine whether exposure to high POP levels is associated with autism diagnosis in the population.

Parental psychiatric disorders and autism spectrum disorders

The present population-based, case-control study examines associations between specific parental psychiatric disorders and autism spectrum disorders (ASD) including childhood autism, Asperger's syndrome and pervasive developmental disorder (PDD-NOS). The cohort includes 4713 children born between 1987 and 2005 with diagnoses of childhood autism, Asperger's syndrome or PDD-NOS. Cases were ascertained from the Finnish Hospital Discharge Register, and each was matched to four controls by gender, date of birth, place of birth, and residence in Finland. Controls were selected from the Finnish Medical Birth Register. Parents were identified through the Finnish Medical Birth Register and Finnish Central Population Register. Parental psychiatric diagnoses from inpatient care were collected from the Finnish Hospital Discharge Register. Conditional logistic regression models were used to assess whether parents' psychiatric disorders predicted ASD after controlling for parents' age, smoking during pregnancy and weight for gestational age. In summary, parental schizophrenia spectrum disorders and affective disorders were associated with the risk of ASD regardless of the subgroup. PDD-NOS was associated with all parental psychiatric disorders investigated. Further studies are needed to replicate these findings. These results may facilitate the investigation of shared genetic and familial factors between ASD and other psychiatric disorders.

Smoking during pregnancy and risk of autism spectrum disorder in a Finnish National Birth Cohort

BACKGROUND

Results of previous population-based studies examining associations between smoking during pregnancy and autism spectrum disorders (ASD) are contradictory. Furthermore, there is a lack of population-based studies examining the relationship between smoking during pregnancy and the main diagnostic subtypes of ASD.

METHODS

We conducted a population-based nested case-control study based on the Finnish Prenatal Study of Autism (FIPS-A) among liveborn infants delivered in Finland between 1987 and 2005. Data on maternal smoking during pregnancy were available from the Finnish Medical Birth Register (FMBR) since October 1990. Data on ASD in the offspring were obtained from the Finnish Hospital Discharge Register (FHDR).

RESULTS

Among the three subtypes of ASD, maternal smoking during the whole pregnancy was associated with an increased risk of pervasive developmental disorder (PDD) (odds ratio 1.2, 95% confidence interval 1.0, 1.5). The increase in odds persisted after controlling for maternal age, mother's socio-economic and psychiatric status, and infant's weight for gestational age. However, smoking exposure limited to the first trimester was not associated with PDD or any of the other ASD subtypes.

CONCLUSIONS

Maternal smoking is related to a modest increase in risk of PDD, while no associations were observed for childhood autism and Asperger's syndrome.

Autism spectrum disorders in IVF children: a national case-control study in Finland

STUDY QUESTION

Does IVF increase the risk of autism spectrum disorders (ASDs)?

SUMMARY ANSWER

No association between IVF and ASDs or any of its subtypes was found in this sample.

WHAT IS KNOWN ALREADY

Certain prenatal factors may increase the risk of ASDs. Studies on the association between IVF and ASDs have shown inconsistent results. IVF is known to increase the risk of perinatal problems but many of them are related to multiple pregnancies.

STUDY DESIGN, SIZE, DURATION

This case-control study included 4164 autistic cases and 16 582 matched controls born in Finland in 1991-2005. The cases were diagnosed with ASDs by the year 2007. The maximum age at diagnosis was 16 years.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Four controls were matched to each case. For singletons the matching criteria were date of birth, place of birth, sex and residency in Finland. For twins the birth order within a twin pair was included as well. In the whole sample, there were 63 cases (1.51%) and 229 controls (1.38%) born after IVF.

MAIN RESULTS AND THE ROLE OF CHANCE

No significant association was found between IVF and ASDs (adjusted odds ratio (OR): 0.9, 95% confidence interval (CI): 0.7-1.3) or its subtypes childhood autism (OR: 0.8, 95% CI: 0.4-1.5), Asperger's syndrome (OR: 0.9, 95% CI: 0.5-1.6) or other pervasive developmental disorder (OR: 1.0, 95% CI: 0.6-1.6). When only singletons were included, there was an association between IVF and Asperger's syndrome in an unadjusted analysis (OR: 2.0, 95% CI: 1.1-3.5) but this was not significant when adjusted for mother's socioeconomic status or parity. When the analyses were conducted separately for boys and girls, there was a significant association between IVF and Asperger's syndrome for boys in an unadjusted analysis (OR: 2.1, 95% CI: 1.2-3.7) but this was not significant in the final adjusted model.

LIMITATIONS, REASONS FOR CAUTION

Information both on IVF and on ASDs was based on registers and it is possible that there is some misclassification. No information on different subtypes of IVF or other assisted reproduction techniques was available. Statistical power may have been insufficient.

WIDER IMPLICATIONS OF THE FINDINGS

This study showed no increased risk of ASDs in children born after IVF but studies with larger sample sizes and information on different subtypes of IVF are needed to confirm the finding.

STUDY FUNDING/COMPETING INTEREST(S)

The study was supported by Autism Speaks, NIMH 1K02-MH65422 and NIEHS 1R01ES019004. There are no competing interests.

Risk of autism spectrum disorders in low birth weight and small for gestational age infants

OBJECTIVE

To examine the relationship between birth weight, gestational age, small for gestational age (SGA), and 3 of the most common autism spectrum disorder (ASD) subtypes.

STUDY DESIGN

In this population-based case-control study conducted in Finland, 4713 cases born between 1987 and 2005 with International Classification of Diseases-diagnoses of childhood autism, Asperger syndrome, or pervasive developmental disorder (PDD), were ascertained from the Finnish Hospital Discharge Register. Four controls, individually matched on sex, date of birth, and place of birth, were selected from the Finnish Medical Birth Register for each case. Conditional logistic regression models were used to assess whether birth weight and gestational age information predicted ASD after controlling for maternal age, parity, smoking during pregnancy, and psychiatric history, as well as for infant's major congenital anomalies.

RESULTS

Very low (<1500 g) and moderately low (<2500 g) birth weight, very low gestational age (less than 32 weeks), and SGA increased risk of childhood autism (adjusted OR 3.05, 95% CI 1.4-6.5; 1.57, 1.1-2.3; 2.51, 1.3-5.0; and 1.72, 1.1-2.6, respectively). Very low and moderately low birth weight, very low gestational age, and SGA were also associated with increase in PDD risk (OR 3.44, 95% CI 1.9-6.3; 1.81, 1.4-2.4; 2.46, 1.4-2.3; and 2.24, 1.7-3.0, respectively). No associations were found between the perinatal characteristics and Asperger syndrome. The increased risks persisted after controlling for selected potential confounders.

CONCLUSIONS

The finding that low birth weight, prematurity, and SGA were related to childhood autism and PDD but not to Asperger syndrome suggests that prenatal factors related to these exposures may differ for these ASD subtypes, which may have preventive implications.

Psychosocial factors associated with becoming a young father in Finland: a nationwide longitudinal study

Background

Little is known about the characteristics of boys who become fathers at young age. Some studies have suggested that antisocial adolescents are more likely to be young fathers. The aim of this study was to examine the associations of psychosocial factors in childhood with becoming a young father, and to assess if they are independent of criminal behavior in adolescence.

Methods

The baseline assessment in 1989 included 2,946 boys born in 1981. Information about psychiatric symptoms at age eight was collected with Rutter questionnaires from parents and teachers and with the Child Depression Inventory from the children themselves. Data on criminal offenses at age 16–20 was collected from a police register. Register-based follow-up data on becoming a father under the age of 22 was available for 2,721 boys.

Results

The factors measured at age eight, which were associated with becoming a young father independently of adolescent criminality, were conduct problems, being born to a young father and having a mother with a low educational level. Having repeatedly committed criminal offences in adolescence was associated with becoming a young father independently of psychosocial factors in childhood.

Conclusions

Antisocial tendencies both in childhood and adolescence are associated with becoming a young father. They should be taken into consideration when designing preventive or supportive interventions.

Autism spectrum disorders in the Stockholm Youth Cohort: design, prevalence and validity

OBJECTIVE

Reports of rising prevalence of autism spectrum disorders (ASD), along with their profound personal and societal burden, emphasize the need of methodologically sound studies to explore their causes and consequences. We here present the design of a large intergenerational resource for ASD research, along with population-based prevalence estimates of ASD and their diagnostic validity.

METHOD

The Stockholm Youth Cohort is a record-linkage study comprising all individuals aged 0-17 years, ever resident in Stockholm County in 2001-2007 (N = 589,114). ASD cases (N = 5,100) were identified using a multisource approach, involving registers covering all pathways to ASD diagnosis and care, and categorized according to co-morbid intellectual disability. Prospectively recorded information on potential determinants and consequences of ASD were retrieved from national and regional health and administrative registers. Case ascertainment was validated through case-note review, and cross validation with co-existing cases in a national twin study.

RESULTS

The 2007 year prevalence of ASD in all children and young people was 11.5 per 1,000 (95% confidence interval 11.2-11.8), with a co-morbid intellectual disability recorded in 42.6% (41.0-44.2) of cases. We found 96.0% (92.0-98.4) of reviewed case-notes being consistent with a diagnosis of ASD, and confirmed ASD in 85.2% (66.2-95.8) of affected twins.

CONCLUSIONS

Findings from this contemporary study accords with recently reported prevalence estimates from Western countries at around 1%, based on valid case ascertainment. The Stockholm Youth Cohort, in light of the availability of extensive information from Sweden's registers, constitutes an important resource for ASD research. On-going work, including collection of biological samples, will enrich the study further.