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Abstract: The objectives of this study were to establish the different developmental trajectories of hyperactive–impulsive behaviors on the basis of both mother and father ratings at 19, 32, 50, and 63 months, and to examine the predictive validity of these trajectories with respect to later hyperactive–impulsive behaviors, as rated by teachers in the first 2 years of school. Hyperactive–impulsive behaviors were assessed in a population-based sample of 1,112 twins (565 boys and 547 girls) at 19, 32, 50, and 63 months of age. The results revealed a differentiated and consistent view of developmental trajectories of hyperactive–impulsive behaviors derived from these repeated assessments, with 7.1% of children seen by mothers (7% for fathers) as displaying high and stable hyperactive–impulsive behaviors. According to mother ratings, children on a high-chronic trajectory were more likely than other children to display hyperactive–impulsive behaviors at 72 and 84 months according to their teachers. Repeated measures over time and father-based trajectories significantly added to the prediction teacher later ratings of hyperactive–impulsive behaviors. These results support the predictive validity of parental assessment of hyperactive–impulsive behaviors during the preschool years and their use to identify children at risk for further evaluation and possible intervention.

Children exposed to family violence, such as child-directed and child-witnessed parental violence, tend to manifest higher levels of antisocial behaviors later in life. Genetically informed studies additionally show that antisocial behaviors are partly inherited. While there is a consensus about the polygenic nature of antisocial behavior, it remains unclear as to whether the differences present at the DNA level moderate the impact of parental violence on antisocial behaviors. This study tested whether children who were the victims of, or who witnessed, family violence exhibit more antisocial behaviors once they reach adolescence and early adulthood, and whether this risk varied according to a serotonergic polygenic index. Participants were 410 male members of the Quebec Longitudinal Study of Kindergarten Children. Child-directed and child-witnessed parental violence and participants’ antisocial behaviors were self-reported or assessed through semi-structured interviews. Previously derived haplotype-based polygenic indexes mapping to 11 serotonergic genes were used. Participants who were the victims of, or witnessed parental violence, were generally at higher risk of manifesting antisocial behaviors. Findings also offered a partial support to prior evidence for gene-environment interactions in some, but not all antisocial outcomes. Participants who were victims of child-directed parental violence and carried lower serotonergic risk were at higher risk of manifesting property or violent crimes in adulthood, supporting the Social-push model. Alternatively, participants who witnessed intra-parental violence were at higher risk of exhibiting symptoms of conduct disorder and antisocial personality disorder if they carried a higher number of haplotypic risk alleles, lending support to the Diathesis-stress model. This study extends prior work by emphasizing the need to separately investigate distinct forms of family violence and to use indicators of risk capturing variants present across multiple genes to better understand their independent and joint contributions to antisocial behaviors over the life course.

The co-occurrence between attention-deficit hyperactivity disorder (ADHD) and physical conditions is frequent but often goes unrecognised. Most available evidence on the links between ADHD and physical conditions relies on cross-sectional studies. Understanding temporal sequences of associations is key to inform appropriate treatment and preventive strategies. We aimed to assess possible longitudinal associations between ADHD symptoms and a broad range of physical conditions, adjusting for several confounding factors.

Research has shown that some people with neuromuscular diseases may have a lower level of education due to lower socioeconomic status and possibly compromised health literacy. In view of these data, it appears important to document their decision-making needs to ensure better support when faced with the decision to participate or not in research projects. 1) To document the decision-making needs of individuals with neuromuscular diseases to participate in research; 2) To explore their preferences regarding the format of knowledge translation tools related to research participation. This qualitative study is based on the Ottawa Decision Support Framework. A two-step descriptive study was conducted to capture the decision-making needs of people with neuromuscular diseases related to research participation: 1) Individual semi-directed interviews (with people with neuromuscular diseases) and focus groups (with healthcare professionals); 2) Synthesis of the literature. The semi-directed interviews (n = 11), the two focus groups (n = 11) and the literature synthesis (n = 50 articles) identified information needs such as learning about ongoing research projects, scientific advances and research results, the potential benefits and risks associated with different types of research projects, and identified values surrounding research participation: helping other generations, trust, obtaining better clinical follow-up, and socialization. This paper provides useful recommendations to support researchers and clinicians in developing material to inform individuals with neuromuscular diseases about research participation.

Background and aims: Serrated lesions (SL) have been associated with significant risks of developing colorectal cancer (CRC). Data on synchronous findings after SL detection during colonoscopy is limited. Study aim was to evaluate the rate of synchronous advanced neoplasia (S-AN) and synchronous CRC (S-CRC) in colonoscopies where SLs were detected. Methods: We conducted a retrospective study of screening aged patients 45–74year with colorectal SL (sessile serrated polyp [SSP] or traditional serrated adenoma [TSA]) detected during an elective colonoscopy. Primary outcome was risk of S-AN in patients with SL. Secondary outcomes included risk of S-AN or S-CRC stratified by SL characteristics. Results: The study included 1262 patients with 1649 SLs (1214 with SSPs and 48 with TSAs). 47.2% were female and 22.9% of exams were screening colonoscopies, 48.2% surveillance, 28.9% diagnostic. The overall rates of S-AN and S-CRC were 15.1% and 1.3%, respectively. Presence of SSPs ≥ 10 mm was associated with higher rates of S-AN, (18.1 vs. 12.2%, Odds-Ratio [OR] = 1.61 [95% Confidence Interval [CI] 1.17–2.23], p= 0.004). SSP dysplasia was predictive of S-AN, (30.3 vs 14.1%, OR = 2.68 [95%CI 1.24–5.78], p= 0.012) but not S-CRC. SSP number (≥ 3) and location (proximal) were not predictors of S-AN or S-CRC. Conclusion: Patients with SLs are at high-risk of S-AN and S-CRC. Findings of SSPs ≥ 10 mm and SSP dysplasia are associated with high-risk of S-AN. Endoscopists should exercise heightened vigilance for synchronous findings when SLs are detected, especially SSPs ≥ 10 mm or when bowel preparation is suboptimal. Studies contrasting synchronous risk of other polyp types are needed to confirm these results.

Objectives: Findings from a birth cohort study indicated that the mental health of young adults had not worsened during the first wave of the COVID-19 pandemic, compared to 2018. This study examined longitudinal changes in mental health between March 2018 and June 2021 in the context of protracted public health mitigation measures about 12 months after the onset of the pandemic. Methods: Participants from the Quebec Longitudinal Study of Child Development (n= 2120 at inception; n= 1461 during the COVID-19 pandemic), a population-based cohort of individuals born in 1997/1998, reported on their depressive and anxiety symptoms as well as suicidal ideation prior to the pandemic in 2018 (age 20), and during the pandemic in the summer of 2020 (age 22) and spring of 2021 (age 23). Results: Depressive (Cohen’s d= 0.15 [95% CI: 0.09 to 0.20]) and anxiety (Cohen’s d= 0.33 [95% CI: 0.27 to 0.39]) symptoms increased between 2018 and 2021 for both males and females, but suicidal ideation did not change. There was also a significant increase in moderate to severe depressive (31.7% to 36.3%) and anxiety (14.7% to 24.8%) symptoms from 2018 to 2021. Youth who were students, those who were experiencing financial stress, food insecurity, and loneliness, and those without pre-existing poor mental health experienced the largest increase in depressive and anxiety symptoms over time. Conclusion: These findings highlight the mental health burden experienced by young adults during the COVID-19 pandemic, highlighting the need for preventive services and continued longitudinal follow-ups of these youths.

Despite the substantial heritability of antisocial behavior (ASB), specific genetic variants robustly associated with the trait have not been identified. The present study by the Broad Antisocial Behavior Consortium (BroadABC) meta-analyzed data from 28 discovery samples (N= 85,359) and five independent replication samples (N= 8058) with genotypic data and broad measures of ASB. We identified the first significant genetic associations with broad ASB, involving common intronic variants in the forkhead box protein P2 (FOXP2) gene (lead SNP rs12536335, p= 6.32 × 10−10). Furthermore, we observed intronic variation in Foxp2 and one of its targets (Cntnap2) distinguishing a mouse model of pathological aggression (BALB/cJ strain) from controls (BALB/cByJ strain). Polygenic risk score (PRS) analyses in independent samples revealed that the genetic risk for ASB was associated with several antisocial outcomes across the lifespan, including diagnosis of conduct disorder, official criminal convictions, and trajectories of antisocial development. We found substantial genetic correlations of ASB with mental health (depression rg= 0.63, insomnia rg= 0.47), physical health (overweight rg= 0.19, waist-to-hip ratio rg= 0.32), smoking (rg= 0.54), cognitive ability (intelligence rg= −0.40), educational attainment (years of schooling rg= −0.46) and reproductive traits (age at first birth rg= −0.58, father’s age at death rg= −0.54). Our findings provide a starting point toward identifying critical biosocial risk mechanisms for the development of ASB.

The comorbidity between physical and mental health conditions is challenging and frequently goes unrecognized in practice. Associations between Attention-Deficit/Hyperactivity Disorder (ADHD) and physical conditions have been reported in youth. However, prior research failed to: (1) address the patterns of associations in early childhood, middle childhood, and adolescence within the same population sample; (2) consider a large set of physical disorders at the same time; (3) take confounders into account. Our goal was to assess the associations between ADHD symptoms and a broad set of physical conditions across developmental periods. This birth cohort study (n= 2057) is the first to explore the associations between ADHD and a wide range of medical conditions by encompassing the whole early development from 5 months to 17 years in the same sample and relying on innovative network analyses. We found significant associations between ADHD symptoms and several physical conditions, some of which were observed in early childhood, middle childhood, and adolescence (e.g., asthma, sleep problems) or were confounded by socioeconomic status or psychiatric comorbidities (e.g., body mass index, dental caries). The study calls for an effective integrated care model encompassing mental and general healthcare across the developmental period.

Commonly comorbid early onset psychiatric disorders might reflect the varying expression of overlapping risk factors. The mediating processes remain poorly understood, but three factors show some promise: adolescent externalizing traits, early life adversity, and midbrain dopamine autoreceptors. To investigate whether these features acquire greater predictive power when combined, a longitudinal study was conducted in youth who have been followed since birth. Cohort members were invited to participate based on externalizing scores between 11 to 16 years of age. At age 18 (age 18.5 ± 0.6 y.o.), 52 entry criteria meeting volunteers had a 90-min positron emission tomography scan with [18F]fallypride, completed the Childhood Trauma Questionnaire, and were assessed with the Structured Clinical Interview for DSM-5. The three-factor model identified those with a lifetime history of DSM-5 disorders with an overall accuracy of 90.4% (p= 2.4 × 10−5) and explained 91.5% of the area under the receiver operating characteristic curve [95% CI: .824, 1.000]. Targeting externalizing disorders specifically did not yield a more powerful model than targeting all disorders (p= 0.54). The model remained significant when including data from participants who developed their first disorders during a three-year follow-up period (p= 3.5 × 10−5). Together, these results raise the possibility that a combination of temperamental traits, childhood adversity, and poorly regulated dopamine transmission increases risk for diverse, commonly comorbid, early onset psychiatric problems, predicting this susceptibility prospectively.

Objectives: The COVID-19 pandemic has been associated with increased mental health problems. We investigated (1) associations between disordered eating in adolescence and mental health problems after one year of the pandemic and (2) the mechanisms explaining associations. Method: We analyzed data from a population-based birth cohort in Quebec, Canada (557 males and 759 females). High and low levels of disordered eating symptom trajectories were previously estimated (age 12, 15, 17, and 20 years). Anxiety, depression, non-suicidal self-injury, and suicidal ideation were assessed at 23 years (March–June 2021). Putative mediators included loneliness and social media use (age 22 years, July–August 2020). Analyses controlled for mental health and socio-economic status at age 10–12 years and were conducted for males and females separately. Results: Females in the high-level disordered eating symptom trajectory were at increased risk for non-suicidal self-injury (OR 1.60; 95% CI 1.02–2.52) and suicidal ideation (2.16; 1.31–3.57), whereas males were at increased risk for severe anxiety (2.49; CI 1.11–5.58). Males and females in the high-level trajectory were more likely to report severe depression (2.26; 1.14–5.92 and 2.15, 1.36–3.38 respectively). Among females, associations were partially explained (17–35%) by loneliness during the first 4 months of the pandemic. Conclusion: Young adults who experienced disordered eating as adolescents were at increased risk of mental health problems during the pandemic. Loneliness partially mediated the effect, suggesting that pandemic mitigation resulting in increased social isolation may have exacerbated mental health problems among women with a history of disordered eating.

Objective: Only a minority of drug and alcohol users develops a substance use disorder. Previous studies suggest that this differential vulnerability commonly reflects a developmental trajectory characterized by diverse externalizing behaviors. In this study, we examined the relation between child and adolescent externalizing behaviors and adolescent substance use in a prospectively followed Canadian birth cohort, accounting for the temporal sequence of a wide variety of contributing factors.Methods: Two hundred and forty-two adolescents followed since birth (date range: 1996 to 2012) were assessed on externalizing behavior (age 17 months to 16 years), alcohol and cannabis use at age 16, age of alcohol use onset, family history of substance use problems, family functioning (age 11 to 15), sensation seeking (age 16), prenatal substance exposure, socioeconomic status (age 1 to 9), and sex.Results: Age of alcohol use onset was predicted by a family history of substance use problems, externalizing traits from ages 6 to 10 and 11 to 16, sensation seeking at age 16, prenatal alcohol and tobacco exposure and family functioning at ages 11 to 15. High frequencies of alcohol and cannabis use at age 16 were both predicted by externalizing traits from ages 11 to 16, a family history of substance use problems and sensation seeking after controlling for other individual, environmental and familial variables. The association between familial substance use problems and substance use during adolescence was partially mediated by externalizing traits from age 11 to 16.Conclusions: The present findings provide prospective evidence for a developmental risk pathway for adolescent substance use, potentially identifying those who could benefit from early interventions.

The excitatory neurotransmitter glutamate has been implicated in experience-dependent neuroplasticity and drug-seeking behaviors. Type 5 metabotropic glutamate (mGlu5) receptors might be particularly important. They are critically involved in synaptic plasticity and their availability has been reported to be lower in people with alcohol, tobacco, and cocaine use disorders. Since these reductions could reflect effects of drug use or pre-existing traits, we used positron emission tomography to measure mGlu5 receptor availability in young adults at elevated risk for addictions. Fifty-nine participants (age 18.5 ± 0.6) were recruited from a longitudinal study that has followed them since birth. Based on externalizing traits that predict future substance use problems, half were at low risk, half were at high risk. Cannabis use histories varied markedly and participants were divided into three subgroups: zero, low, and high use. Compared to low risk volunteers, those at elevated risk had lower [11C]ABP688 binding potential (BPND) values in the striatum, amygdala, insula, and orbitofrontal cortex (OFC). Cannabis use by risk group interactions were observed in the striatum and OFC. In these regions, low [11C]ABP688 BPNDvalues were only seen in the high risk group that used high quantities of cannabis. When these high risk, high cannabis use individuals were compared to all other participants, [11C]ABP688 BPNDvalues were lower in the striatum, OFC, and insula. Together, these results provide evidence that mGlu5 receptor availability is low in youth at elevated risk for addictions, particularly those who frequently use cannabis.

The neurobiological traits that confer risk for addictions remain poorly understood. However, dopaminergic function throughout the prefrontal cortex, limbic system, and upper brainstem has been implicated in behavioral features that influence addiction vulnerability, including poor impulse control, and altered sensitivity to rewards and punishments (i.e., externalizing features). To test these associations in humans, we measured type-2/3 dopamine receptor (DA2/3R) availability in youth at high vs. low risk for substance use disorders (SUDs). In this study, N= 58 youth (18.5 ± 0.6 years) were recruited from cohorts that have been followed since birth. Participants with either high (high EXT; N= 27; 16 F/11 M) or low pre-existing externalizing traits (low EXT; N= 31; 20 F/11 M) underwent a 90-min positron emission tomography [18F]fallypride scan, and completed the Barratt Impulsiveness Scale (BIS-11), Substance Use Risk Profile scale (SURPS), and Sensitivity to Punishment (SP) and Sensitivity to Reward (SR) questionnaire. We found that high vs. low EXT trait participants reported elevated substance use, BIS-11, SR, and SURPS impulsivity scores, had a greater prevalence of psychiatric disorders, and exhibited higher [18F]fallypride binding potential (BPND) values in prefrontal, limbic and paralimbic regions, even when controlling for substance use. Group differences were not evident in midbrain dopamine cell body regions, but, across all participants, low midbrain BPNDvalues were associated with low SP scores. Together, the results suggest that altered DA2/3R availability in terminal extra-striatal and dopamine cell body regions might constitute biological vulnerability traits, generating an EXT trajectory for addictions with and without co-occurring alterations in punishment sensitivity (i.e., an internalizing feature).

Eating-disorder symptoms, such as body image issues, maladaptive behaviors, and preoccupation with weight, tend to develop in adolescence. However, it is unclear whether early childhood characteristics or behaviours could be indicators of a risk of developing eating-disorder symptoms later. The current study examined the possible link between certain early behaviours (e.g., hyperactivity, childhood eating), early cognitive processes, and eating-disorder symptoms development in a community cohort followed from birth. Results showed that being hyperactive in early childhood predicts higher levels of eating-disorder symptoms at the beginning of adolescence (age 15), and that this is partially explained by a link between being hyperactive, being more rigid in our ways of thinking, and engaging in overeating behaviours. Additionally, more early rigid ways of thinking predicted the increase in symptoms over time. Our results demonstrate possible behaviours and characteristics that could be used to identify children at risk of eating disorders, which in future research could potentially help improve our preventive interventions.

The insertion of a subclavian central venous catheter is generally associated with a high rate of success and a favorable risk profile. The use of ultrasound for procedural guidance has been demonstrated to further increase the rate of success and reduce the risk of specific mechanical complications, especially in patients with difficult surface anatomy. Many individual ultrasound techniques have been described in the literature; this article presents a systematic approach for incorporating these tools into bedside practice and includes a series of illustrative figures and narrated video presentations to demonstrate the techniques described.

BACKGROUND:Exposure to peer victimization is relatively common. However, little is known about its developmental course and its effect on impairment associated with mental illnesses. We aimed to identify groups of children following differential trajectories of peer victimization from ages 6 to 13 years and to examine predictive associations of these trajectories with mental health in adolescence.METHODS:Participants were members of the Quebec Longitudinal Study of Child Development, a prospective cohort of 2120 children born in 1997/98 who were followed until age 15 years. We included 1363 participants with self-reported victimization from ages 6 to 13 years and data available on their mental health status at 15 years.RESULTS:We identified 3 trajectories of peer victimization. The 2 prevailing groups were participants with little or moderate exposure to victimization (441/1685 [26.2%] and 1000/1685 [59.3%], respectively); the third group (244 [14.5%]) had been chronically exposed to the most severe and long-lasting levels of victimization. The most severely victimized individuals had greater odds of reporting debilitating depressive or dysthymic symptoms (odds ratio [OR] 2.56, 95% confidence interval [CI] 1.27–5.17), debilitating generalized anxiety problems (OR 3.27, CI 1.64–6.51) and suicidality (OR 3.46, CI 1.53–7.81) at 15 years than those exposed to the lowest levels of victimization, after adjustment for sex, childhood mental health, family hardship and victimization perpetration. The association with suicidality remained significant after controlling for concurrent symptoms of depression or dysthymia and generalized anxiety problems.INTERPRETATION:Adolescents who were most severely victimized by peers had an increased risk of experiencing severe symptoms consistent with mental health problems. Given that peer victimization trajectories are established early on, interventions to reduce the risk of being victimized should start before enrolment in the formal school system.

Growing evidence suggests that children’s participation in early childhood education and care (ECEC), especially center-based services, is associated with positive outcomes, particularly for children over one year of age and children of low socioeconomic backgrounds. This signals an important opportunity for reducing socioeconomic disparities in young children’s development. Many western countries have adopted policies to encourage maternal employment, facilitate ECEC service use, or both, often focusing on disadvantaged families. Yet few studies to date have tested the impact of these policies for reducing socioeconomic selection into ECEC. This study integrates data from five cohorts of children living in different western, high-income countries (UK, USA, Netherlands, Canada, and Norway; total N= 21,437). We compare participation rates and socioeconomic selection into ECEC across the different policy contexts in infancy (5–9 months) and early childhood (36–41 months). Policy environments where parents had access to at least 6 months of paid maternity/parental leave had lower ECEC participation in infancy but higher participation in early childhood. Higher participation rates were also associated with universal ECEC subsidies (i.e., not targeted to low-income families). In general, low income, low maternal education and having more than one child were associated with reduced use of ECEC. Selection effects related to low income and number of children were reduced in countries with universal ECEC subsidies when out-of-pocket fees were income-adjusted or reduced for subsequent children, respectively. Most socioeconomic selection effects were reduced in Norway, the only country to invest more than 1% of its GDP into early childhood. Nevertheless, low maternal education was consistently associated with reduced use of ECEC services across all countries. Among families using services however, there were few selection effects for the type of ECEC setting (center-based vs. non-center-based), particularly in early childhood. In sum, this comparative study suggests wide variations in ECEC participation that can be linked to the policy context, and highlights key policy elements which may reduce socioeconomic disparities in ECEC use.

Eating disorders, typically involving preoccupation with eating, excessive exercise, and body image issues, are particularly common in adolescence. However, their evolution over time remains unclear as certain signs and symptoms may appear sooner than others. The current study studied the development of eating disorder symptoms in a community cohort followed from birth to adulthood. This study describes trajectories of eating disorder symptoms and risk from age 12 to 20 in both boys and girls. Results showed that the largest increase in eating disorder symptoms occurs between 12 and 15 years of age, both in overall symptomatology as well as in specific symptoms such as loss-of-control when eating, feeling overweight, and attributing importance to food. Additionally, more girls than boys appeared at risk for eating disorders, although the patterns represented by the trajectories were similar in both sexes. Our results highlight the importance of starting early prevention programs before the beginning of adolescence, when symptoms usually start to manifest.

Using a 17-year longitudinal design, this study examined the role of personal and family factors assessed early in life, and also academic and social experiences assessed in the first year of college, in predicting college completion. We followed a sample of 444 French-speaking Canadian children from middle to upper socioeconomic backgrounds (66% boys and 34% girls; 6 years old at study onset). We assessed social behaviors (i.e., aggressive-disruptive, anxiety-withdrawal, and prosocial behaviors), mothers’ child-rearing practices (i.e., discipline and pleasure), and family resources (i.e., family structure, mothers’ education, and mothers’ age at the birth of the first child) at kindergarten; academic records in elementary and high school; and academic and social integration in college (i.e., adjustment to academic requirements, academic success, participation in social activities, and attachment to the institution). College completion at age 23 years was obtained from national official records. Using logistic regression analysis, we found that previous social behaviors, academic records, and family experiences had greater impact on college completion than did the quality of students’ academic and social integration in college. We propose some avenues to better understand how precollege factors can improve a child's academic trajectory, college aspirations, and chances of success.

IMPORTANCE: Childhood sleepwalking and sleep terrors are 2 parasomnias with a risk of serious injury for which familial aggregation has been shown. OBJECTIVES: To assess the prevalence of sleepwalking and sleep terrors during childhood; to investigate the link between early sleep terrors and sleepwalking later in childhood; and to evaluate the degree of association between parental history of sleepwalking and presence of somnambulism and sleep terrors in children. DESIGN, SETTING, AND PARTICIPANTS: Sleep data from a large prospective longitudinal cohort (the Quebec Longitudinal Study of Child Development) of 1940 children born in 1997 and 1998 in the province were studied from March 1999 to March 2011. MAIN OUTCOMES AND MEASURES: Prevalence of sleep terrors and sleepwalking was assessed yearly from ages 11/2 and 21/2 years, respectively, to age 13 years through a questionnaire completed by the mother. Parental history of sleepwalking was also queried. RESULTS: The peak of prevalence was observed at 11/2 years for sleep terrors (34.4% of children; 95% CI, 32.3%-36.5%) and at age 10 years for sleepwalking (13.4%; 95% CI, 11.3%-15.5%). As many as one-third of the children who had early childhood sleep terrors developed sleepwalking later in childhood. The prevalence of childhood sleepwalking increases with the degree of parental history of sleepwalking: 22.5% (95% CI, 19.2%-25.8%) for children without a parental history of sleepwalking, 47.4% (95% CI, 38.9%-55.9%) for children who had 1 parent with a history of sleepwalking, and 61.5% (95% CI, 42.8%-80.2%) for children whose mother and father had a history of sleepwalking. Moreover, parental history of sleepwalking predicted the incidence of sleep terrors in children as well as the persistent nature of sleep terrors. CONCLUSIONS AND RELEVANCE: These findings substantiate the strong familial aggregation for the 2 parasomnias and lend support to the notion that sleepwalking and sleep terrors represent 2 manifestations of the same underlying pathophysiological entity.

DNA methylation patterns are characterized by highly conserved developmental programs, but allow for divergent gene expression resulting from stochastic epigenetic drift or divergent environments. Genome-wide methylation studies in monozygotic (MZ) twins are providing insight into the extent of epigenetic variation that occurs, irrespective of genotype. However, little is known about the variability of DNA methylation patterns in adolescence, a period involving significant and rapid physical, emotional, social, and neurodevelopmental change. Here, we assessed genome-wide DNA methylation using the 450 K Illumina BeadChip in a sample of 37 MZ twin pairs followed longitudinally since birth to investigate: 1) the extent of variation in DNA methylation in identical genetic backgrounds in adolescence and; 2) whether these variations are randomly distributed or enriched in particular functional pathways. We also assessed stability of DNA methylation over 3–6 months to distinguish stable trait-like and variable state-like genes. A pathway analysis found high within-pair variability in genes associated with development, cellular mechanisms, tissue and cell morphology, and various disorders. Test-retest analyses performed in a sub-sample of 8 twin pairs demonstrated enrichment in gene pathways involved in organismal development, cellular growth and proliferation, cell signaling, and particular disorders. The variability found in functional gene pathways may plausibly underlie phenotypic differences in this adolescent MZ twin sample. Furthermore, we assessed stability of methylation over 3–6 months and found that some genes were stable while others were unstable, suggesting that the methylome remains dynamic in adolescence and that dynamic sites tend to be organized in certain gene pathways.