Development of atopic disease and disturbed sleep in childhood and adolescence--a longitudinal population-based study

BACKGROUND

Both atopic diseases and sleep disturbances have increased during recent decades, especially in children. Sleep is important for many aspects of immune regulation relevant in allergic diseases, and sleep disturbances are common in patients with such diseases. A connection between sleep disturbances and fatigue, and atopic disease is well established. However, the time course and putative causal relationships between these factors are obscure.

OBJECTIVE

We aimed at investigating the developmental relationships between subjectively reported sleep disturbances and symptoms of atopic disease, from childhood to adolescence.

METHODS

This longitudinal study used parent-report questionnaire data on symptoms of atopic disease, and sleep disturbances, from the Twin Study of Child and Adolescent Development (TCHAD). Overall, 1480 twin pairs born in Sweden were approached first when children were 8-9 years old, and again later at 13-14 years old. Response rates were 75% and 72%. Data from the TCHAD questionnaires were linked to the Swedish Medical Birth Register based on personal identification numbers.

RESULTS

Being overtired at age 8 increased the risk [OR; 95% CI (2.59; 1.31-5.11)] to develop rhinitis symptoms at age 13, even when controlling for gender, previous rhinitis, Socio-economic status, birth weight and other sleep disturbances at age 8. Likewise, symptoms of asthma at age 8 was an independent risk factor for being overtired at age 13 [OR; 95% CI (2.64; 1.44-4.84)], controlling for similar confounders.

CONCLUSION & CLINICAL RELEVANCE

The findings from this study are consonant with the proposition that atopic disease and disturbed sleep are more than passively interrelated. Future research needs to delineate whether causal relationships between these problems are at hand and, if so, at what periods in development this applies. These results point to a need for clinicians to investigate sleep difficulties and treat impaired sleep in paediatric patients with atopic disease.

Genetic and environmental risk factors in males for self-report externalizing traits in mid-adolescence and criminal behavior through young adulthood

BACKGROUND

Externalizing traits or behaviors are typically assessed by self-report scales or criminal records. Few genetically informative studies have used both methods to determine whether they assess the same genetic or environmental risk factors.

METHOD

We examined 442 male Swedish twin pairs with self-reported externalizing behaviors at age 16–17 years [externalizing traits (EXT), self-reported delinquency (SRD), impulsivity (IMP), grandiosity (GRD) and callousness (CLS)] and criminal behavior (CB) from the National Suspect Registry from age 13 to 25 years. Multivariate structural equation modeling was conducted with Mx.

RESULTS

The best-fit model contained one genetic, one shared environmental and two non-shared environmental common factors, and variable specific genetic and non-shared environmental factors. The risk for CB was influenced substantially by both genetic (a2=0.48) and familial–environmental factors (c2=0.22). About one-third of the genetic risk for CB but all of the shared environmental risk was indexed by the self-report measures. The degree to which the individual measures reflected genetic versus familial–environmental risks for CB varied widely. GRD and CLS were correlated with CB mainly through common genetic risk factors. SRD and CB covaried largely because of shared familial–environmental factors. For EXT and IMP, observed correlations with CB resulted in about equal parts from shared genetic and shared familial–environmental factors.

CONCLUSIONS

In adolescence, measures of grandiose and callous temperament best tap the genetic liability to CB.Measures of antisocial behaviors better index familial–environmental risks for CB. A substantial proportion of the genetic risk to CB was not well reflected in any of the self-report measures.

Different heritabilities but shared etiological influences for parent, teacher and self-ratings of ADHD symptoms: an adolescent twin study

BACKGROUND

Parent and teacher ratings of attention deficit hyperactivity disorder (ADHD) symptoms yield high estimates of heritability whereas self-ratings typically yield lower estimates. To understand why, the present study examined the etiological overlap between parent, teacher and self-ratings of ADHD symptoms in a population-based sample of 11-12-year-old twins. Method Participants were from the Twins Early Development Study (TEDS). ADHD symptoms were assessed using the Strengths and Difficulties Questionnaire (SDQ) hyperactivity scale completed by parents, teachers and children. Structural equation modeling was used to examine genetic and environmental contributions to phenotypic variance/covariance.

RESULTS

The broad-sense heritability of ADHD symptoms was 82% for parent ratings, 60% for teacher ratings and 48% for self-ratings. Post-hoc analyses revealed significantly higher heritability for same-teacher than different-teacher ratings of ADHD (76% v. 49%). A common pathway model best explained the relationship between different informant ratings, with common genetic influences accounting for 84% of the covariance between parent, teacher and self-rated ADHD symptoms. The remaining variance was explained by rater-specific genetic and non-shared environmental influences.

CONCLUSIONS

Despite different heritabilities, there were shared genetic influences for parent, teacher and self-ratings of ADHD symptoms, indicating that different informants rated some of the same aspects of behavior. The low heritability estimated for self-ratings and different-teacher ratings may reflect increased measurement error when different informants rate each twin from a pair, and/or greater non-shared environmental influences. Future studies into the genetic influences on ADHD should incorporate informant data in addition to self-ratings to capture a pervasive, heritable component of ADHD symptomatology.

Stimulant and non-stimulant attention deficit/hyperactivity disorder drug use: total population study of trends and discontinuation patterns 2006-2009

OBJECTIVE

To explore the prevalence and discontinuation of dispensed medications for attention deficit/hyperactivity disorder (ADHD) drugs from 2006 to 2009.

METHOD

A total population cohort of all individuals aged 6-45 years, alive and registered as residents in Sweden during any calendar year from 2006 to 2009 (N = 5 149 791) included 41 700 patients dispensed with an ADHD drug (methylphenidate, atomoxetine, amphetamine, or dexamphetamine). The dispensing prevalence was calculated for each year, stratified on sex and age. A longitudinal analysis was also performed to compare the rates of treatment discontinuation across the strata.

RESULTS

The dispensing prevalence increased from 2.93 per 1000 in 2006 to 6.98 in 2009 (PR = 2.38, 95% CI = 2.34-2.43). The prevalence ratio (PR) was 3.40 for adults, 22-45 years old; 2.41 for adolescents, 15-21 years old; and 1.90 for children aged 6-14. The increase was also greater in women than in men (PR = 2.92 vs. 2.19). Patients aged 15-21 were the most likely to discontinue treatment; after 3 years and 11 months, 27% of those patients were still under treatment.

CONCLUSION

From 2006 to 2009, the number of prescriptions dispensed for ADHD drugs increased substantially. The rate of treatment discontinuation in the age interval 15-21 is higher than expected considering the persistence rates of the disorder.

Parental schizophrenia and increased offspring suicide risk: exploring the causal hypothesis using cousin comparisons

BACKGROUND

Little is known about suicide risk among offspring of parents hospitalized for schizophrenia and the mechanisms behind this association.

METHOD

We applied a nested case-control design based on linkage of Swedish population-based registers. Among 12- to 30-year-old offspring, we identified 68 318 offspring with suicidal behavior (attempted and completed suicide) and their parents. Five healthy control-parent pairs were matched to each suicidal case-parent pair and conditional logistic regression used to obtain odds ratios (ORs). Further, to disentangle familial confounding from causal environmental mechanisms, we compared the population-based suicide risk with the risk found within full-cousins and half-cousins differentially exposed to parental schizophrenia.

RESULTS

Offspring of parents with schizophrenia had significantly increased suicide risk after accounting for socio-economic status, parental suicidal behavior and offspring mental illness [OR 1.68, 95% confidence interval (CI) 1.53-1.85]. Suicide risks in offspring of schizophrenic mothers and fathers were similar in magnitude; so were risks across different developmental periods. Importantly, offspring suicide risk remained essentially unchanged across genetically different relationships; offspring of siblings discordant for schizophrenia had equivalent risk increases within full-cousins (OR 1.96, 95% CI 1.66-2.31) and half-cousins (OR 1.69, 95% CI 1.17-2.44).

CONCLUSIONS

Parental schizophrenia was associated with increased risk of offspring suicidal behavior, independent of gender of the schizophrenic parent, and persisting into adulthood. The suicide risk in offspring remained at a similar level when comparing genetically different relationships, which suggests that at least part of the association is due to environmental mechanisms. These findings should inspire increased attention to suicidal ideation and prevention efforts in offspring of parents with schizophrenia.

Genetic innovation and stability in externalizing problem behavior across development: a multi-informant twin study

The use of cross-informant ratings in previous longitudinal studies on externalizing behavior may have obscured the presence of continuity of genetic risk. The current study included latent factors representing the latent estimates of externalizing behavior based on both parent and self-report which eliminated rater-specific effects from these latent estimates. Symptoms of externalizing behavior of 1,480 Swedish twin pairs were obtained at ages 8-9, 13-14, 16-17 and 19-20 both by parent and self-report. Mx modeling was used to estimate additive genetic, shared and specific environmental influences. Genetic continuity was found over the entire developmental period as well as additional sources of genetic influence emerging around early and late adolescence. New unique environmental effects (E) on externalizing behavior arose early in adolescence. The results support both the presence of genetic continuity and change in externalizing behavior during adolescence due to newly emerging genetic and environmental risk factors.

Genetic and environmental influences on adult attention deficit hyperactivity disorder symptoms: a large Swedish population-based study of twins

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) frequently persists into adulthood. Family and twin studies delineate a disorder with strong genetic influences among children and adolescents based on parent- and teacher-reported data but little is known about the genetic and environmental contribution to DSM-IV ADHD symptoms in adulthood. We therefore aimed to investigate the impact of genetic and environmental influences on the inattentive and hyperactive-impulsive symptoms of ADHD in adults.

METHOD

Twin methods were applied to self-reported assessments of ADHD symptoms from a large population-based Swedish twin study that included data from 15 198 Swedish male and female twins aged 20 to 46 years.

RESULTS

The broad heritability [i.e., A + D, where A is an additive genetic factor and D (dominance) a non-additive genetic factor] was 37% (A = 11%, D = 26%) for inattention and 38% (A = 18%, D = 20%) for hyperactivity-impulsivity. The results also indicate that 52% of the phenotypic correlation between inattention and hyperactivity-impulsivity (r = 0.43) was explained by genetic influences whereas the remaining part of the covariance was explained by non-shared environmental influences. These results were replicated across age strata.

CONCLUSIONS

Our findings of moderate broad heritability estimates are consistent with previous literature on self-rated ADHD symptoms in older children, adolescents and adults and retrospective reports of self-rated childhood ADHD by adults but differ from studies of younger children with informant ratings. Future research needs to clarify whether our data indicate a true decrease in the heritability of ADHD in adults compared to children, or whether this relates to the use of self-ratings in contrast to informant data.

Country-specific birth weight and length in type 1 diabetes high-risk HLA genotypes in combination with prenatal characteristics

OBJECTIVE

To examine the relationship between high-risk human leukocyte antigen (HLA) genotypes for type 1 diabetes and birth size in combination with prenatal ch aracteristics in different countries.

STUDY DESIGN

Four high-risk HLA genotypes were enrolled in the Environmental determinants of Diabetes in the Young study newborn babies from the general population in Finland, Germany, Sweden and the United States. Stepwise regression analyses were used to adjust for country, parental physical characteristics and environmental factors during pregnancy.

RESULT

Regression analyses did not reveal differences in birth size between the four type 1 diabetes high-risk HLA genotypes. Compared with DQ 4/8 in each country, (1) DQ 2/2 children were heavier in the United States (P=0.028) mostly explained however, by parental weight; (2) DQ 2/8 (P=0.023) and DQ 8/8 (P=0.046) children were longer in Sweden independent of parents height and as well as (3) in the United States for DQ 2/8 (P=0.023), but again dependent on parental height.

CONCLUSION

Children born with type 1 diabetes high-risk HLA genotypes have comparable birth size. Longitudinal follow-up of these children should reveal whether birth size differences between countries contribute to the risk for islet autoimmunity and type 1 diabetes.

A twin study of autism symptoms in Sweden

This study aimed to identify empirically the number of factors underlying autism symptoms-social impairments, communication impairments, and restricted repetitive behaviors and interests-when assessed in a general population sample. It also investigated to what extent these autism symptoms are caused by the same or different genetic and environmental influences. Autistic symptoms were assessed in a population-based twin cohort of >12,000 (9- and 12-year-old) children by parental interviews. Confirmatory factor analyses, principal component analyses and multivariate structural equation model fitting were carried out. A multiple factor solution was suggested, with nearly all analyses pointing to a three-factor model for both boys and girls and at both ages. A common pathway twin model fit the data best, which showed that there were some underlying common genetic and environmental influences across the different autism dimensions, but also significant specific genetic effects on each symptom type. These results suggest that the autism triad consists of three partly independent dimensions when assessed in the general population, and that these different autism symptoms, to a considerable extent, have partly separate genetic influences. These findings may explain the large number of children who do not meet current criteria for autism but who show some autism symptoms. Molecular genetic research may benefit from taking a symptom-specific approach to finding genes associated with autism.

Association between childhood asthma and ADHD symptoms in adolescence--a prospective population-based twin study

BACKGROUND

Cross-sectional studies report a relationship between childhood asthma and attention-deficit hyperactivity disorder (ADHD) symptoms, but the mechanisms are yet unclear. Our objective was to investigate the longitudinal link between childhood asthma and the two dimensions of ADHD (hyperactivity-impulsivity, HI, and inattention, IN) in adolescence. We also aimed to explore the genetic and environmental contributions and the impact of asthma medication.

METHODS

Data on asthma, HI and IN, birth weight, socioeconomic status, zygosity, and medication were collected from the Swedish Medical Birth Register and through parental questionnaires at ages 8-9 and 13-14 years on 1480 Swedish twin pairs born 1985-1986. The association between asthma at age 8-9 and ADHD symptoms at age 13-14 was assessed with generalized estimating equations, and twin analyses to assess the genetic or environmental determinants were performed.

RESULTS

Children with asthma at age 8-9 had an almost twofold increased risk of having one or more symptom of HI (OR 1.88, 95% CI 1.18-3.00) and a more than twofold increased risk to have three symptoms or more of HI (OR 2.73, 95% CI 1.49-5.00) at age 13-14, independent of asthma medication. For IN, no significant relationship was seen. Results from twin modeling indicate that 68% of the phenotypic correlation between asthma and HI (r=0.23, 0.04-0.37) was because of genetic influences.

CONCLUSIONS

Our findings suggest that childhood asthma is associated with subsequent development of HI in early adolescence, which could be partly explained by genetic influences. Early strategies to identify children at risk may reduce burden of the disease in adolescence.

Sex differences and developmental stability in genetic and environmental influences on psychoactive substance consumption from early adolescence to young adulthood

BACKGROUND

Genetic and environmental factors are important in the etiology of substance use. However, little is known about the stability of these factors across development. We aimed to answer three crucial questions about this etiology that have never been addressed in a single study: (1) Is there a general vulnerability to substance consumption from early adolescence to young adulthood? (2) If so, do the genetic and environmental influences on this vulnerability change across development? (3) Do these developmental processes differ in males and females?

METHOD

Subjects included 1480 twin pairs from the Swedish Twin Study of Child and Adolescent Development who have been followed since 1994. Prospective, self-reported regular smoking, alcohol intoxication and illicit drug use were assessed at ages 13-14, 16-17 and 19-20 years. Structural modeling was performed with the program Mx.

RESULTS

An underlying common factor accounted for the association between smoking, alcohol and illicit drug consumption for the three age groups. Common genetic and shared environmental effects showed substantial continuity. In general, as participants aged, the influence of the shared environment decreased, and genetic effects became more substance specific in their effect.

CONCLUSIONS

The current report answers three important questions in the etiology of substance use. The genetic and environmental risk for substance consumption is partly mediated through a common factor and is partly substance specific. Developmentally, evidence was strongest for stability of common genetic effects, with less evidence for genetic innovation. These processes seem to be the same in males and females.

Rheumatoid arthritis and birth outcomes: a Danish and Swedish nationwide prevalence study

OBJECTIVES

To examine the prevalence of preterm birth, infants with low Apgar score, small for gestational age (SGA) birth, stillbirth and congenital abnormalities in women with rheumatoid arthritis (RA) compared with women without RA.

DESIGN

Prevalence study.

SETTING

Combined Sweden and Denmark nationwide from 1994 to 2006.

SUBJECTS

We included 871,579 women with a first-time singleton birth identified through population-based healthcare databases.

MAIN OUTCOME MEASURES

We compared the prevalence of preterm birth, low Apgar score (<7 at 5 min), SGA birth, stillbirth and congenital abnormalities amongst women with RA compared with women without RA using prevalence odds ratio (OR) with 95% confidence interval (95% CI), whilst controlling for maternal age, smoking, parental cohabitation and year. We stratified analyses by period of birth (1994-1997, 1998-2001 and 2002-2006).

RESULTS

Amongst 1199 women with RA, 7.8% gave birth between 32 and 36 gestational weeks (adjusted OR, 1.44; 95% CI, 1.14-1.82), 1.4% gave birth before gestational week 32 (adjusted OR, 1.55; 95% CI, 0.97-2.47), 1.6% had an infant with a low Apgar score (OR, 0.99; 95% CI, 0.95-1.65), 5.9% had an SGA birth (adjusted OR, 1.56; 95% CI, 1.2-2.01), 0.9% experienced stillbirth (adjusted OR, 2.07; 95% CI, 0.98-4.35) and 4.3% gave birth to an infant with congenital abnormalities (adjusted OR,1.32; 95% CI, 0.98-1.79). The OR for congenital abnormalities decreased from 2.57 (95% CI, 1.59-4.16) in 1994-1997 to 1.00 (95% CI, 0.64-1.56) in 2002-2006.

CONCLUSIONS

Women with RA had a high prevalence of most adverse birth outcomes. This could be due to inflammatory activity, medical treatment or other factors not controlled for.

Genetic and environmental influences on the risk of acute appendicitis in twins

BACKGROUND

Acute appendicitis is common but the aetiology is unclear. This study examined the heritability of acute appendicitis.

METHODS

The study included twin pairs with known zygosity born between 1959 and 1985. Individuals with acute appendicitis were found by record linkage with the Swedish Inpatient Register. Comparing monodizygotic and dizygotic twins, the similarity and relative proportions of phenotypic variance resulting from genetic and environmental factors were analysed. Risks of acute appendicitis explained by heritability and environmental effects were estimated.

RESULTS

Some 3441 monozygotic and 2429 dizygotic twins were identified. Almost no genetic effects were found in males (8 (95 per cent confidence interval 0 to 50) per cent), but shared (31 (0 to 49) per cent) and non-shared (61 (47 to 74) per cent) environmental factors accounted for this risk. In females, the heritability was estimated as 20 (0 to 36) per cent and the remaining variation was due to non-shared environmental factors (80 (64 to 98) per cent). For the sexes combined, genetic effects accounted for 30 (5 to 40) per cent and non-shared environmental effects for 70 (60 to 81) per cent of the risk.

CONCLUSION

Acute appendicitis has a complex aetiology with sex differences in heritability and environmental factors.