Genetic overlap between impulsivity and alcohol dependence: a large-scale national twin study

BACKGROUND

Alcohol dependence is associated with increased levels of impulsivity, but the genetic and environmental underpinnings of this overlap remain unclear. The purpose of the current study was to investigate the degree to which genetic and environmental factors contribute to the overlap between alcohol dependence and impulsivity.

METHOD

Univariate and bivariate twin model fitting was conducted for alcohol dependence and impulsivity in a national sample of 16 819 twins born in Sweden from 1959 to 1985.

RESULTS

The heritability estimate for alcohol dependence was 44% [95% confidence interval (CI) 31-57%] for males and 62% (95% CI 52-72%) for females. For impulsivity, the heritability was 33% (95% CI 30-36%) in males and females. The bivariate twin analysis indicated a statistically significant genetic correlation between alcohol dependence and impulsivity of 0.40 (95% CI 0.23-0.58) in males and 0.20 (95% CI 0.07-0.33) in females. The phenotypic correlation between alcohol dependence and impulsivity was 0.20 and 0.17 for males and females, respectively, and the bivariate heritability was 80% (95% CI 47-117%) for males and 53% (95% CI 19-86%) for females. The remaining variance in all models was accounted for by non-shared environmental factors.

CONCLUSIONS

The association between alcohol dependence and impulsivity can be partially accounted for by shared genetic factors. The genetic correlation was greater in men compared with women, which may indicate different pathways to the development of alcohol dependence between sexes. The observed genetic overlap has clinical implications regarding treatment and prevention, and partially explains the substantial co-morbidity between alcohol dependence and psychiatric disorders characterized by impulsive behaviour.

Impact of asthma medication and familial factors on the association between childhood asthma and attention-deficit/hyperactivity disorder: a combined twin- and register-based study: Epidemiology of Allergic Disease

BACKGROUND

Asthma and attention-deficit/hyperactivity disorder (ADHD) are prevalent in childhood and may cause functional impairment and stress in families. Previous research supports an association between asthma and ADHD in children, but several aspects of this relationship are unclear.

OBJECTIVE

Our aim was to study whether the association between asthma and ADHD is restricted to either the inattentive or the hyperactive/impulsive symptoms of ADHD, to explore the impact of asthma severity and asthma medication and the contribution of shared genetic and environmental risk factors on the asthma-ADHD relationship.

METHODS

Data on asthma, ADHD, zygosity and possible confounders were collected from parental questionnaires at 9 or 12 years on 20 072 twins through the Swedish Twin Register, linked to the Swedish Medical Birth Register, the National Patient Register and the Prescribed Drug Register. The association between asthma and ADHD, the impact of asthma severity and medication, was assessed by generalized estimating equations. Cross-twin-cross-trait correlations (CTCT) were estimated to explore the relative importance of genes and environment for the association.

RESULTS

Asthmatic children had a higher risk of also having ADHD [odds ratio (OR) 1.53, 95% confidence interval (CI): 1.16-2.02]. The association was not restricted to either of the two dimensions of ADHD. The magnitude of the association increased with asthma severity (OR 2.84, 95% CI: 1.86-4.35) for ≥ 4 asthma attacks in the last 12 months and was not affected by asthma treatment. The CTCTs possibly indicate that the genetic component in overlap of the disorders is weak.

CONCLUSIONS AND CLINICAL RELEVANCE

Childhood asthma, especially severe asthma, is associated with ADHD. Asthma medication seems not to increase the risk of ADHD. Clinicians should be aware of the potential of ADHD in asthma. Optimal asthma care needs to be integrated with effective evaluation and treatment of ADHD in children with co-existing disorders.

Population-based, multi-generational family clustering study of social anxiety disorder and avoidant personality disorder

BACKGROUND

We aimed to provide unbiased estimates of familial risk and heritability of social anxiety disorder (SAD) and avoidant personality disorder (AVPD).

METHOD

We identified 18 399 individuals diagnosed with SAD and 2673 with AVPD in the Swedish National Patient Register between 1997 and 2009. Risks (odds ratios; OR) for SAD in all biological and non-biological relatives of probands, compared to relatives of unaffected individuals were calculated. We also estimated the risks for AVPD in relatives of probands with SAD.

RESULTS

The risk for SAD among relatives of SAD probands increased proportionally to the degree of genetic relatedness. The risks for first-degree relatives [OR 4.74, 95% confidence interval (CI) 4.28-5.25] were significantly higher than for second-degree and third-degree relatives. Second-degree relatives (OR 2.30, 95% CI 2.01-2.63) had significantly higher risk than third-degree relatives (OR 1.72, 95% CI 1.52-1.94). Relatives at similar genetic distances had similar risks for SAD, despite different degrees of shared environment. Heritability was estimated to be approximately 56%. There were no significant sex differences in the familial patterns. The risk of AVPD in relatives of SAD probands was significantly elevated, even after excluding individuals with both diagnoses (first-degree OR 3.54, second-degree OR 2.20, third-degree OR 1.62). Non-biological relatives (spouses/partners) also had elevated risks for both SAD (OR 4.01) and AVPD (OR 3.85).

CONCLUSIONS

SAD clusters in families primarily due to genetic factors. SAD and AVPD are aetiologically related and may represent different expressions of the same vulnerability. The strong marital concordance observed in SAD/AVPD may indicate assortative mating but the exact mechanisms and implications require further investigation.

Effects of predicted climatic changes on distribution of organic contaminants in brackish water mesocosms

Predicted consequences of future climate change in the northern Baltic Sea include increases in sea surface temperatures and terrestrial dissolved organic carbon (DOC) runoff. These changes are expected to alter environmental distribution of anthropogenic organic contaminants (OCs). To assess likely shifts in their distributions, outdoor mesocosms were employed to mimic pelagic ecosystems at two temperatures and two DOC concentrations, current: 15°C and 4 mg DOCL(-1) and, within ranges of predicted increases, 18°C and 6 mg DOCL(-1), respectively. Selected organic contaminants were added to the mesocosms to monitor changes in their distribution induced by the treatments. OC partitioning to particulate matter and sedimentation were enhanced at the higher DOC concentration, at both temperatures, while higher losses and lower partitioning of OCs to DOC were observed at the higher temperature. No combined effects of higher temperature and DOC on partitioning were observed, possibly because of the balancing nature of these processes. Therefore, changes in OCs' fates may largely depend on whether they are most sensitive to temperature or DOC concentration rises. Bromoanilines, phenanthrene, biphenyl and naphthalene were sensitive to the rise in DOC concentration, whereas organophosphates, chlorobenzenes (PCBz) and polychlorinated biphenyls (PCBs) were more sensitive to temperature. Mitotane and diflufenican were sensitive to both temperature and DOC concentration rises individually, but not in combination.

Intellectual disability and cognitive ability in Darier disease: Swedish nation-wide study

BACKGROUND

Darier disease is an autosomal dominant skin disorder caused by mutations in the ATP2A2 gene. Anecdotal reports suggest a relationship between Darier disease and intellectual disabilities, but these reports are based on small clinical samples and limited by absence of control populations.

OBJECTIVES

To examine the risk of intellectual disability and subclinical impairments in cognitive ability in Darier disease.

METHODS

We conducted a matched cohort study based on Swedish Population-, Patient- and Conscript Registers. The risk of being diagnosed with intellectual disability was estimated in 770 individuals with Darier disease, compared with matched comparison individuals without Darier disease. Associations were examined with risk ratios from conditional logistic regressions. In addition, we analysed test-based cognitive ability data (i.e. IQ data) from the Swedish conscript examination, for a subset of patients without diagnosed intellectual disability.

RESULTS

Individuals with Darier disease had a sixfold increased risk of being diagnosed with intellectual disability (risk ratio 6.2, 95% confidence interval 3.1-12.4). For conscripted individuals with Darier disease but no diagnosed intellectual disability, mean cognitive ability scores were about half a standard deviation lower than for comparison subjects.

CONCLUSIONS

Darier disease is associated with intellectual disability and subclinical impairments in cognitive ability. The Darier-causing mutations merit further attention in molecular genetic research on intellectual disability and cognitive ability.

Comparative Investigation of Postoperative Complications in Patients With Gastroesophageal Junction Cancer Treated With Preoperative Chemotherapy or Surgery Alone

Background and aim:

Gastroesophageal junction cancer is one of the leading causes to cancer-related death and the prognosis is poor. However, progress has been made over the last couple of decades with the introduction of multimodality treatment and optimized surgery. Three-year survival rates have improved to 50% in patients receiving neoadjuvant therapy. Only a few studies have focused on the difference of postoperative complications in patients receiving neoadjuvant therapy in relation to a comparative surgery-only group. The aim of this study was to compare the prevalence of postoperative complications of patients with cancer at the gastroesophageal junction treated with either neoadjuvant chemotherapy or surgery alone in patients from “The Danish Clinical Registry of Carcinomas of the Esophagus, the Gastro-Esophageal Junction and the Stomach.”

Materials and methods:

A historical follow-up study, comparing postoperative complications between two cohorts before and after implementation of chemotherapy was completed.

Results:

In all, 180 consecutive patients treated with perioperative chemotherapy and a comparative surgery-only group of patients were identified from The Danish Clinical Registry of Carcinomas of the Esophagus, the Gastro-Esophageal Junction and the Stomach. No difference was found in demographics between the two groups, except for alcohol consumption and a lower T and N stage in the surgery-only group, and no difference in complication rates was found. Furthermore, no variable in the multivariate analysis was significantly associated with anastomotic leakage which was considered the most severe complication.

Conclusion:

Since perioperative chemotherapy does not appear to increase surgical complications, the future challenges include defining the optimal combination of chemo- and/or radiotherapy, but more importantly also to select the patients who will benefit the most from the different neoadjuvant strategies.

Conversion from clinically isolated syndrome to multiple sclerosis: A large multicentre study

Background and objective:

We explored which clinical and biochemical variables predict conversion from clinically isolated syndrome (CIS) to clinically definite multiple sclerosis (CDMS) in a large international cohort.

Methods:

Thirty-three centres provided serum samples from 1047 CIS cases with at least two years’ follow-up. Age, sex, clinical presentation, T2-hyperintense lesions, cerebrospinal fluid (CSF) oligoclonal bands (OCBs), CSF IgG index, CSF cell count, serum 25-hydroxyvitamin D3 (25-OH-D), cotinine and IgG titres against Epstein-Barr nuclear antigen 1 (EBNA-1) and cytomegalovirus were tested for association with risk of CDMS.

Results:

At median follow-up of 4.31 years, 623 CIS cases converted to CDMS. Predictors of conversion in multivariable analyses were OCB (HR = 2.18, 95% CI = 1.71–2.77, p < 0.001), number of T2 lesions (two to nine lesions vs 0/1 lesions: HR = 1.97, 95% CI = 1.52–2.55, p < 0.001; >9 lesions vs 0/1 lesions: HR = 2.74, 95% CI = 2.04–3.68, p < 0.001) and age at CIS (HR per year inversely increase = 0.98, 95% CI = 0.98–0.99, p < 0.001). Lower 25-OH-D levels were associated with CDMS in univariable analysis, but this was attenuated in the multivariable model. OCB positivity was associated with higher EBNA-1 IgG titres.

Conclusions:

We validated MRI lesion load, OCB and age at CIS as the strongest independent predictors of conversion to CDMS in this multicentre setting. A role for vitamin D is suggested but requires further investigation.

The co-occurrence of autistic and ADHD dimensions in adults: an etiological study in 17,770 twins

Autism spectrum disorder (ASD) and attention deficit/hyperactivity disorder (ADHD) often occur together. To obtain more insight in potential causes for the co-occurrence, this study examined the genetic and environmental etiology of the association between specific ASD and ADHD disorder dimensions. Self-reported data on ASD dimensions social and communication difficulties (ASDsc), and repetitive and restricted behavior and interests (ASDr), and ADHD dimensions inattention (IA), and hyperactivity/impulsivity (HI) were assessed in a community sample of 17,770 adult Swedish twins. Phenotypic, genetic and environmental associations between disorder dimensions were examined in a multivariate model, accounting for sex differences. ASDr showed the strongest associations with IA and HI in both sexes (r(p) 0.33 to 0.40). ASDsc also correlated moderately with IA (females r(p) 0.29 and males r(p) 0.35) but only modestly with HI (females r(p) 0.17 and males r(p) 0.20). Genetic correlations ranged from 0.22 to 0.64 and were strongest between ASDr and IA and HI. Sex differences were virtually absent. The ASDr dimension (reflecting restricted, repetitive and stereotyped patterns of behavior, interests and activities) showed the strongest association with dimensions of ADHD, on a phenotypic, genetic and environmental level. This study opens new avenues for molecular genetic research. As our findings demonstrated that genetic overlap between disorders is dimension-specific, future gene-finding studies on psychiatric comorbidity should focus on carefully selected genetically related dimensions of disorders.

Offspring death and subsequent psychiatric morbidity in bereaved parents: addressing mechanisms in a total population cohort

BACKGROUND

It is unclear if psychiatric morbidity among parents bereaved of a child is related to major loss in general or if the cause of death matters. Whether such a link is consistent with a causal explanation also remains uncertain.

METHOD

We identified 3,114,564 parents through linkage of Swedish nationwide registers. Risk of psychiatric hospitalization was assessed with log-linear Poisson regression and family-based analyses were used to explore familial confounding.

RESULTS

A total of 3284 suicides and 14,095 any-cause deaths were identified in offspring between 12 and 25 years of age. Parents exposed to offspring suicide had considerably higher risk of subsequent psychiatric hospitalization than unexposed parents [relative risk (RR) 1.90, 95% confidence interval (CI) 1.72-2.09], higher than parents exposed to offspring non-suicide death relative to controls (RR 1.18, 95% CI 1.11-1.26). We found no risk increase among stepfathers differentially exposed to biologically unrelated stepchildren's death or suicide, and the relative risk was notably lower among full siblings differentially exposed to offspring death or suicide.

CONCLUSIONS

Parental psychiatric hospitalization following offspring death was primarily found in offspring suicide. Familial (e.g. shared genetic) effects seemed important, judging from both lack of psychiatric hospitalization in bereaved stepfathers and attenuated risk when bereaved parents were contrasted to their non-bereaved siblings. We conclude that offspring suicide does not 'cause' psychiatric hospitalization in bereaved parents.

Effects of grazer presence on genetic structure of a phenotypically diverse diatom population

Studies of predator-prey systems in both aquatic and terrestrial environments have shown that grazers structure the intraspecific diversity of prey species, given that the prey populations are phenotypically variable. Populations of phytoplankton have traditionally considered comprising only low intraspecific variation, hence selective grazing as a potentially structuring factor of both genetic and phenotypic diversity has not been comprehensively studied. In this study, we compared strain specific growth rates, production of polyunsaturated aldehydes, and chain length of the marine diatom Skeletonema marinoi in both grazer and non-grazer conditions by conducting monoclonal experiments. Additionally, a mesocosm experiment was performed with multiclonal experimental S. marinoi populations exposed to grazers at different levels of copepod concentration to test effects of grazer presence on diatom diversity in close to natural conditions. Our results show that distinct genotypes of a geographically restricted population exhibit variable phenotypic traits relevant to grazing interactions such as chain length and growth rates. Grazer presence affected clonal richness and evenness of multiclonal Skeletonema populations in the mesocosms, likely in conjunction with intrinsic interactions among the diatom strains. Only the production of polyunsaturated aldehydes was not affected by grazer presence. Our findings suggest that grazing can be an important factor structuring diatom population diversity in the sea and emphasize the importance of considering clonal differences when characterizing species and their role in nature.

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.

Behçet's disease and close contact with pigs

Six male patients out of seven with Behçet's disease were found to have a very similar and close contact with pigs and pork. These six cases are reported and we ask the question whether the contacts with pigs are just coincidental findings or whether an external agent, e.g. a virus, could be forwarded to man from pigs and pork. Immune complex associated vasculitis is described e.g. in patients with hepatitis B and the same mechanisms might be operating in patients with Behçet's disease.

Reversal of increased whole blood and plasma viscosity after treatment of hypothyroidism in man

Blood and plasma viscosity was measured in 13 patients with hypothyroidism before and during replacement therapy with l-thyroxine. Blood viscosity was measured at natural hematocrit and after adjustment to 40%. The values were compared to those of 12 healthy subjects. Both blood viscosity at hematocrit 40% and plasma viscosity were increased in the hypothyroid state and decreased to the levels of the reference group after treatment. The therapy-induced changes in blood and plasma viscosity were intercorrelated at low but not at high shear rates. The changes in viscosity were not correlated to the reductions in lipoprotein concentrations resulting from therapy. The institution of l-thyroxine replacement therapy was also followed by reductions in erythrocyte sedimentation rate and diastolic blood pressure, both with significant correlations to the decrease in blood viscosity. It is concluded that in hypothyroidism there are changes in both plasma and erythrocytes that increase blood viscosity, with normalization upon treatment with l-thyroxine to euthyroidism.

Increased whole blood and plasma viscosity in patients with angina pectoris and "normal" coronary arteries

Blood and plasma viscosity was measured in eight patients with typical effort-induced angina pectoris who did not have coronary artery stenosis at angiography. The same variables were studied in 14 patients with angina pectoris and verified coronary artery disease that in most cases was extensive. Both groups of patients had significantly higher viscosity values in whole blood, at natural hematocrit as well as standardized hematocrit (45%), than 25 healthy subjects serving as a reference group. Plasma viscosity was also significantly elevated in both patient groups. The patients without coronary artery stenosis had as high blood and plasma viscosity values as had the stenosis group. It is concluded that increased blood and plasma viscosity should be added to the list of pathological findings in patients with angina pectoris in the absence of organic coronary artery stenosis.

Involvement of kappa-opioid receptors in visceral nociception in mice

It has been shown that the behavioural responses to chemically evoked visceral nociception are increased in transgenic mice lacking the kappa-opioid receptor (KOR). The aim of the present study was to evaluate the contribution of KOR in mechanically evoked visceral pain by performing colorectal distension (CRD) and monitoring the subsequent visceromotor response (VMR) in control mice (KOR(+/+)) and in mice lacking KOR (KOR(-/-)). Pseudo-affective visceral pain responses were evoked in conscious mice using increasing (10-80 mmHg) and repeated (12 x 55 mmHg) phasic CRD paradigms. The resulting VMR was determined by monitoring the electromyographic activity of the abdominal muscle. The increasing and repeated CRD paradigms, respectively, evoked similar responses in both KOR(+/+) and KOR(-/-) mice. The selective KOR-agonists U-69593 (5 and 25 mg kg(-1), s.c.) and asimadoline (25 mg kg(-1), s.c.) significantly decreased the VMR in KOR(+/+) mice, while having no effect in KOR(-/-) mice. In contrast, the selective mu-opioid receptor agonist fentanyl significantly reduced the VMR in both types of mice and appeared more efficacious in KOR(-/-) mice. The opioid receptor antagonist naloxone (0.3-30 mg kg(-1) s.c.) did not affect the response to CRD in C57BL/6 mice at any dose tested. In conclusion, the data confirm that the KOR agonists used in this study inhibit the VMR to CRD in mice by acting via KOR receptors. In addition, the data suggest that the endogenous opioid system is not likely to modulate the VMR to mechanically evoked visceral pain in mice.

Effects of pregabalin on visceral pain responses and colonic compliance in rats

BACKGROUND AND PURPOSE

Pregabalin, which binds to the alpha2-delta subunit of voltage-gated calcium channels, increased the threshold for pain during colorectal distension (CRD) in irritable bowel syndrome (IBS) patients. We tested the effects of oral pregabalin on the visceral pain-related viscerosomatic and autonomic cardiovascular responses to CRD and colonic compliance in rats.

EXPERIMENTAL APPROACH

The activity of the abdominal musculature (viscerosomatic response), monitored by electromyography and intracolonic manometry, and changes in blood pressure and heart rate, monitored by telemetry, were assessed simultaneously in conscious rats during CRD.

KEY RESULTS

Pregabalin (10-200 micromol kg(-1), p.o.) inhibited dose dependently the viscerosomatic response to phasic, noxious CRD (12 distensions at 80 mm Hg). At 200 mumol kg(-1), pregabalin also reduced the increase in blood pressure and heart rate associated with noxious CRD. Moreover, pregabalin (200 micromol kg(-1), p.o.) reduced the visceromotor response to ascending phasic CRD (10-80 mm Hg) and significantly increased the threshold pressure for response. During phasic CRD (2-20 mm Hg), pregabalin (200 micromol kg(-1), p.o.) increased intracolonic volume, resulting in a shift to the left of the pressure-volume relationship curve, indicative of an increase of compliance.

CONCLUSIONS AND IMPLICATIONS

Pregabalin reduced the viscerosomatic and autonomic responses associated with CRD-induced visceral pain and increased colonic compliance in rats. These observations confirm the analgesic activity of pregabalin on visceral pain and support the translational value of the CRD model to humans. Ligands for the alpha2-delta subunit might represent interesting compounds for the treatment of visceral pain disorders, such as IBS.

Risk of bacteraemia and mortality in patients with haematological malignancies

This study examined the association between type of haematological malignancy, risk of bacteraemia and risk of mortality, with emphasis on the impact of bacteraemia type on mortality. A population-based cohort design was used, and all patients aged > or = 15 years with an incident haematological malignancy who were living in North Jutland County, Denmark, during 1992-2002 were included in the study. Among 1666 patients with an incident haematological malignancy, 358 (21%) suffered an episode of bacteraemia during a median follow-up period of 1.1 years (quartile 0.2-3.4) from the date of cancer diagnosis (overall incidence rate of 96/1000 person-years). In comparison to Hodgkin's disease, adjusted incidence rate ratios (IRRs) were 23.3 (95% CI, 10.0-54.5) for acute myeloid leukaemia, 3.8 (95% CI, 1.5-9.3) for multiple myeloma, and 2.2 (95% CI, 0.9-5.1) for non-Hodgkin's lymphoma or chronic lymphatic leukaemia. Overall cumulative 30-day mortality was 32% (95% CI, 27-37), and 90-day mortality was 50% (95% CI, 44-55). In comparison with acute myeloid leukaemia, adjusted mortality rate ratios (MRRs) were close to 1.0 for other haematological malignancies. In comparison to bacteraemia caused by Gram-positive bacteria, adjusted MRRs were 1.0 (95% CI, 0.6-1.5) for Gram-negative bacteraemia, and 1.9 (95% CI, 1.1-3.3) for polymicrobial bacteraemia or fungaemia. Thus, the risk of bacteraemia varied greatly according to the type of malignancy, while mortality rates were similar for these diseases, although dependent on the type of bacteraemia. Polymicrobial bacteraemia or fungaemia was associated with higher mortality.