Dissecting the polygenic contribution of attention-deficit/hyperactivity disorder and autism spectrum disorder on school performance by their relationship with educational attainment.

Attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorders (ASD) are strongly associated with educational attainment (EA), but little is known about their genetic relationship with school performance and whether these links are explained, in part, by the genetic liability of EA. Here, we aim to dissect the polygenic contribution of ADHD and ASD to school performance, early manifestation of psychopathology and other psychiatric disorders and related traits by their relationship with EA. To do so, we tested the association of polygenic scores for EA, ADHD and ASD with school performance, assessed whether the contribution of the genetic liability of ADHD and ASD to school performance is influenced by the genetic liability of EA, and evaluated the role of EA in the genetic overlap between ADHD and ASD with early manifestation of psychopathology and other psychiatric disorders and related traits in a sample of 4,278 school-age children. The genetic liability for ADHD and ASD dissected by their relationship with EA show differences in their association with school performance and early manifestation of psychopathology, partly mediated by ADHD and ASD symptoms. Genetic variation with concordant effects in ASD and EA contributes to better school performance, while the genetic variation with discordant effects in ADHD or ASD and EA is associated with poor school performance and higher rates of emotional and behavioral problems. Our results strongly support the usage of the genetic load for EA to dissect the genetic and phenotypic heterogeneity of ADHD and ASD, which could help to fill the gap of knowledge of mechanisms underlying educational outcomes.

Patterns of Physical Activity of Adolescents With ADHD in the School Context: A Cross-Sectional Study for Clinical Practice.

OBJECTIVES: To describe the daily Physical Activity (PA) patterns of adolescents with Attention-deficit/hyperactivity disorder (ADHD), to analyze the differences in terms of PA patterns between adolescents with ADHD and those without ADHD, and to study the factors associated with achieving the daily PA recommendations. METHODS: The sample was composed of 778 adolescents who provided complete information on their PA patterns through the Physical Activity Questionnaire for Adolescents (PAQ-A). Of these, 97 had ADHD according to DSM-5 criteria. RESULTS: The results show that being a girl or being of foreign origin and having ADHD have an impact on the achievement of the recommended amount of daily PA. CONCLUSIONS: When promoting PA in adolescents with ADHD within the school environment, it is necessary to consider different domains and specific contexts of a school day, paying special attention to girls and adolescents with ADHD of immigrant origin.

The impact of attention-deficit/hyperactivity disorder and specific learning disorders on academic performance in Spanish children from a low-middle- and a high-income population.

Introduction: Past research has demonstrated that attention-deficit/hyperactivity disorder (ADHD), specific learning disorders (SLD), and socioeconomic status (SES) affect a host of educational outcomes. However, there are no studies examining whether SES moderates the association between these neurodevelopmental disorders (ND) and the academic achievement of children and adolescents. The present investigation examined the impact of ADHD and SLD on academic performance in 1,287 Spanish students aged 5-17 from a low-middle (LM)- and a high-income population, when adjusted for comorbidity and demographic factors that may influence educational functioning. Methods: Parents completed a questionnaire regarding demographic data along with the Strengths and Difficulties Questionnaire. Additionally, teachers provided information on learning difficulties trough the Protocol for Detection and Management of Dyslexia. Teacher's Version. Academic performance across multiple domains (i.e., first language, foreign language, mathematics) was obtained from school records. ND were determined using standardized diagnostic methods based on the Diagnostic and Statistical Manual of Mental Disorders criteria. To examine the effects of ADHD and SLD on academic achievement and the potential moderating role of SES, a series of ordinal logistic regressions were conducted. Results: Emotional/behavioral problems, learning difficulties, and ND were more frequent among individuals from the LM-income population. After controlling for gender, age, parental divorce/separation, grade retention, frequency of screen use, and daily meals, both ADHD and SLD were associated with worse educational outcomes. Lower SES also increased the risk for academic impairment, although the interactions with ADHD or SLD were not significant. Conclusion: These findings indicate that ADHD and SLD exert a pervasive impact on academic performance across different socioeconomic backgrounds. Therefore, early detection and effective intervention strategies aimed at students with these ND are crucial to improve their educational functioning and mitigate the negative consequences related to academic problems.

The Sleep Disturbance Scale for Children: psychometric properties and prevalence of sleep disorders in Spanish children aged 6-16 years.

The present research aimed to investigate, for the first time, the validity and reliability of the Sleep Disturbance Scale for Children (SDSC) in a sample of 2733 Spanish children aged 6-16 years. We also described the prevalence and sociodemographic correlates of sleep disorder symptoms among young people, which had never been studied in Spain. Confirmatory factor analysis supported the original six-factor model and Cronbach's alpha for the total questionnaire was 0.82, which indicated good reliability. Moreover, all the SDSC subscales correlated positively and significantly with the total score (range = 0.41-0.70), thus showing convergent validity. Considering T-scores >70 as pathological, we identified at least one sleep disorder in 116 participants (4.24%), including disorders of excessive somnolence (DOES; 5.82%), sleep-wake transition disorders (SWTD; 5.27%), and disorders of initiating and maintaining sleep (DIMS; 5.09%) among the most common problems. Students in secondary education and those from families with a low socioeconomic status were more likely to have DIMS, disorders of arousal, and DOES. Subjects with clinically elevated levels of sleep breathing disorders were more frequently of foreign origin and from disadvantaged families. Boys and primary school students were more prone to sleep hyperhidrosis, while SWTD were overrepresented among children with a low socioeconomic status. According to our results, the Spanish version of the SDSC seems to be a good instrument for assessing sleep disturbances in school-age children and adolescents, which is essential to prevent the significant implications of poor sleeping on the overall welfare of young people.

Changes in the Mental Health of Children and Adolescents during the COVID-19 Lockdown: Associated Factors and Life Conditions.

This study investigated the psychological impact of the coronavirus disease 2019 (COVID-19) among youth by analyzing their emotional/behavioral problems before and during the long-lasting lockdown in Spain. For that purpose, 699 parents with children aged 6-17 and 552 adolescents aged 12-17, who completed the parent and adolescent version of the Strengths and Difficulties Questionnaire at the beginning of 2019, responded to a survey from 26 May to 15 June 2020 that assessed psychological well-being and life conditions during quarantine (i.e., sociodemographic characteristics, situation before the lockdown, physical environment and accompaniment during the lockdown, COVID-related variables). According to both parent- and self-reports, children and youth experienced a significant worsening in emotional symptoms, conduct problems, hyperactivity/inattention, peer problems, and total difficulties subscales. Findings also suggested that impairment was mainly associated with variables related to the child's situation prior to home quarantine, the quality and quantity of the child's social networks during the lockdown, the daily routines the child followed, the concerns the child had about health, and the presence of economic and learning problems caused by the COVID-19. Thus, the present investigation emphasizes the need for carefully monitoring the mental health of younger people, provides guidance for the development of interventions that mitigate some of the psychological difficulties faced in a situation of confinement, and highlights the importance of paying special attention to high-risk groups.

The impact of psychopathology on academic performance in school-age children and adolescents.

Psychiatric symptoms have consistently been associated with negative educational outcomes. However, possible confounding variables, such as comorbid mental and environmental conditions, have not been well addressed. This study examined whether mental health problems were significantly linked to academic performance in a Spanish school-based sample, after adjustment for co-occurring psychiatric symptoms and multiple contextual factors. Parents completed a questionnaire regarding child's sociodemographic characteristics (i.e., gender, age, type of school, socioeconomic status, ethnicity), stressful events (i.e., adoption, parental divorce/separation, grade retention) and lifestyle (i.e., diet, sleep, screen time), along with the Child Behavior Checklist (CBCL). Academic performance was obtained from school records. The sample comprised 7036 students aged 5-17 with full data on the CBCL. Mixed-effects ordinal logistic regression analyses were conducted to investigate the association between psychopathology and academic achievement, controlling for potential confounders. When examined separately, higher scores on the CBCL scales were related to lower grades, regardless of sociodemographic factors. However, after controlling for the presence of other psychiatric symptoms, we found that students who reported more anxious/depressed and thought problems were less likely to perform poorly, while those with increased levels of attention problems and delinquent behavior had higher risk for academic underachievement. These associations remained mainly the same once stressful events and lifestyle were taken into account. This investigation demonstrates that anxious/depressed symptoms, thought problems, attention problems, and delinquent behavior are independently associated with academic performance, which emphasize the need for preventive and treatment interventions targeted at students' mental health to improve their psychological well-being and functioning at school.

Neurodevelopmental disorders among Spanish school-age children: prevalence and sociodemographic correlates.

BACKGROUND: Prevalence estimates of neurodevelopmental disorders (ND) are essential for treatment planning. However, epidemiological research has yielded highly variable rates across countries, including Spain. This study examined the prevalence and sociodemographic correlates of ND in a school sample of Spanish children and adolescents. METHODS: The Child Behaviour Checklist/Teacher's Report Form/Youth Self-Report and the Conners' Rating Scales were administered for screening purposes. Additionally, teachers provided information on reading and writing difficulties. Subjects who screened positive were interviewed for diagnostic confirmation according to the Diagnostic and Statistical Manual of Mental Disorders criteria. The final population comprised 6834 students aged 5-17. Multivariate analyses were performed to determine the influence of gender, age, educational stage, school type, socioeconomic status (SES), and ethnicity on the prevalence estimates. RESULTS: A total of 1249 (18.3%) subjects met criteria for at least one ND, although only 423 had already received a diagnosis. Specifically, the following prevalence rates were found: intellectual disabilities (ID), 0.63%; communication disorders, 1.05%; autism spectrum disorder (ASD), 0.70%; attention-deficit/hyperactivity disorder (ADHD), 9.92%; specific learning disorder (SLD), 10.0%; and motor disorders, 0.76%. Students of foreign origin and from low SES evidenced higher odds of having ID. Boys were more likely to display ASD or a motor disorder. Age, SES, and ethnicity were significant predictors for SLD, while communication disorders and ADHD were also associated with gender. CONCLUSIONS: The prevalence of ND among Spanish students is consistent with international studies. However, a substantial proportion had never been previously diagnosed, which emphasise the need for early detection and intervention programmes.

Psychiatric disorders and comorbidity in a Spanish sample of prisoners at the end of their sentence: Prevalence rates and associations with criminal history.

Introduction: This study examined, for the first time, the prevalence of mental disorders and comorbidities among inmates who were about to be released, and their association with criminal history. Methods: A Spanish sample of 140 prisoners at the end of their sentence was recruited from an occupational program. Psychiatric disorders were determined according to the Diagnostic and Statistical Manual of Mental Disorders criteria. Bivariate analyses followed by multivariate regression models were conducted to identify significant variables for repeat incarceration and violent offending. Results: The lifetime prevalence of Axis I disorders was 81.4%, with substance use disorders (SUD) and attention deficit/hyperactivity disorder (ADHD) being the most common diagnoses (51.4 and 31.4%, respectively). The current prevalence of Axis I disorders was 59.0%, including learning disorders (38.6%), ADHD (16.4%), and SUD (5.71%) among the most frequent syndromes. Thirty-six (26.5%) participants met criteria for a current Axis II disorder, which commonly was an antisocial personality disorder (12.5%). The majority of the sample (60.8%) suffered from two or more comorbid disorders during their lifetime, although the current prevalence fell to 23.3%. Childhood ADHD increased the number of imprisonments, while inmates convicted of a violent crime were more likely to present a learning disorder. Having a lifetime diagnosis of SUD or multiple psychiatric disorders appeared to be associated with both repeat incarceration and violent offending. Conclusion: Given the high rate of mental disorders still present among subjects completing prison sentences and the challenges they may encounter to benefit from vocational programs, our results suggest that appropriate psychiatric care should be provided during imprisonment and after release to facilitate their community reintegration.

Strengths and Difficulties Questionnaire: Psychometric Properties and Normative Data for Spanish 5- to 17-Year-Olds.

The Strengths and Difficulties Questionnaire (SDQ) has been extensively used to measure common forms of psychopathology among children and adolescents. However, its psychometric properties vary across countries and several controversial issues warrant further investigation. This study aimed to evaluate whether the Spanish version of the SDQ is a reliable and valid tool for assessing emotional and behavioral problems in a sample of 6,775 students aged 5 to 17 years, as rated by parents, teachers, and youth. We examined the internal consistency of the questionnaire, its factor structure, and measurement invariance across child's gender and age. Criterion validity was tested against the Child Behavior Checklist (CBCL), Teacher's Report Form (TRF), and Youth Self-Report (YSR), and we measured the ability of the SDQ to identify children with specific psychiatric disorders. Finally, we provide, for the first time, Spanish normative data for children aged 5 to 10 and 11 to 17 years, according to gender and each informant. Our results revealed acceptable reliability estimates for all SDQ subscales. Confirmatory factor analysis supported the original five-factor model and full measurement invariance was found. Furthermore, SDQ scores showed a moderate to strong correlation with those on the equivalent CBCL/TRF/YSR scales, and were effective in discriminating individuals with and without clinical diagnoses.

Epigenome-wide association study of attention-deficit/hyperactivity disorder in adults.

Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable neurodevelopmental disorder that often persists into adulthood. There is growing evidence that epigenetic dysregulation participates in ADHD. Given that only a limited number of epigenome-wide association studies (EWASs) of ADHD have been conducted so far and they have mainly focused on pediatric and population-based samples, we performed an EWAS in a clinical sample of adults with ADHD. We report one CpG site and four regions differentially methylated between patients and controls, which are located in or near genes previously involved in autoimmune diseases, cancer or neuroticism. Our sensitivity analyses indicate that smoking status is not responsible for these results and that polygenic risk burden for ADHD does not greatly impact the signatures identified. Additionally, we show an overlap of our EWAS findings with genetic signatures previously described for ADHD and with epigenetic signatures for smoking behavior and maternal smoking. These findings support a role of DNA methylation in ADHD and emphasize the need for additional efforts in larger samples to clarify the role of epigenetic mechanisms on ADHD across the lifespan.

Shared genetic background between children and adults with attention deficit/hyperactivity disorder.

Attention deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder characterized by age-inappropriate symptoms of inattention, impulsivity, and hyperactivity that persist into adulthood in the majority of the diagnosed children. Despite several risk factors during childhood predicting the persistence of ADHD symptoms into adulthood, the genetic architecture underlying the trajectory of ADHD over time is still unclear. We set out to study the contribution of common genetic variants to the risk for ADHD across the lifespan by conducting meta-analyses of genome-wide association studies on persistent ADHD in adults and ADHD in childhood separately and jointly, and by comparing the genetic background between them in a total sample of 17,149 cases and 32,411 controls. Our results show nine new independent loci and support a shared contribution of common genetic variants to ADHD in children and adults. No subgroup heterogeneity was observed among children, while this group consists of future remitting and persistent individuals. We report similar patterns of genetic correlation of ADHD with other ADHD-related datasets and different traits and disorders among adults, children, and when combining both groups. These findings confirm that persistent ADHD in adults is a neurodevelopmental disorder and extend the existing hypothesis of a shared genetic architecture underlying ADHD and different traits to a lifespan perspective.

Attention-deficit/hyperactivity disorder and lifetime cannabis use: genetic overlap and causality.

Attention-deficit/hyperactivity disorder (ADHD) is a severely impairing neurodevelopmental disorder with a prevalence of 5% in children and adolescents and of 2.5% in adults. Comorbid conditions in ADHD play a key role in symptom progression, disorder course and outcome. ADHD is associated with a significantly increased risk for substance use, abuse and dependence. ADHD and cannabis use are partly determined by genetic factors; the heritability of ADHD is estimated at 70-80% and of cannabis use initiation at 40-48%. In this study, we used summary statistics from the largest available meta-analyses of genome-wide association studies (GWAS) of ADHD (n = 53,293) and lifetime cannabis use (n = 32,330) to gain insights into the genetic overlap and causal relationship of these two traits. We estimated their genetic correlation to be r2 = 0.29 (P = 1.63 × 10-5) and identified four new genome-wide significant loci in a cross-trait analysis: two in a single variant association analysis (rs145108385, P = 3.30 × 10-8 and rs4259397, P = 4.52 × 10-8) and two in a gene-based association analysis (WDPCP, P = 9.67 × 10-7 and ZNF251, P = 1.62 × 10-6). Using a two-sample Mendelian randomization approach we found support that ADHD is causal for lifetime cannabis use, with an odds ratio of 7.9 for cannabis use in individuals with ADHD in comparison to individuals without ADHD (95% CI (3.72, 15.51), P = 5.88 × 10-5). These results substantiate the temporal relationship between ADHD and future cannabis use and reinforce the need to consider substance misuse in the context of ADHD in clinical interventions.

Genome-wide analysis of emotional lability in adult attention deficit hyperactivity disorder (ADHD).

Emotional lability is strongly associated with Attention Deficit Hyperactivity Disorder (ADHD), represents a major source of impairment and predicts poor clinical outcome in ADHD. Given that no specific genes with a role in the co-occurrence of both conditions have been described, we conducted a GWAS of emotional lability in 563 adults with ADHD. Despite not reaching genome-wide significance, the results highlighted genes related with neurotransmission, cognitive function and a wide range of psychiatric disorders that have emotional lability as common clinical feature. By constructing polygenic risk scores on mood instability in the UK Biobank sample and assessing their association with emotional lability in our clinical dataset, we found suggestive evidence of common genetic variation contributing to emotional lability in general population and in clinically diagnosed ADHD. Although not conclusive, these tentative results are in agreement with previous studies that suggest emotion dysregulation as a transdiagnostic construct and highlight the need for further investigation to disentangle the genetic basis of mood instability in ADHD and co-occurring psychiatric disorders.

Epigenetic signature for attention-deficit/hyperactivity disorder: identification of miR-26b-5p, miR-185-5p, and miR-191-5p as potential biomarkers in peripheral blood mononuclear cells.

Attention-deficit/hyperactivity disorder (ADHD) is one of the most prevalent neurodevelopmental disorders in childhood and persists into adulthood in 40-65% of cases. Given the polygenic and heterogeneous architecture of the disorder and the limited overlap between genetic studies, there is a growing interest in epigenetic mechanisms, such as microRNAs, that modulate gene expression and may contribute to the phenotype. We attempted to clarify the role of microRNAs in ADHD at a molecular level through the first genome-wide integrative study of microRNA and mRNA profiles in peripheral blood mononuclear cells of medication-naive individuals with ADHD and healthy controls. We identified 79 microRNAs showing aberrant expression levels in 56 ADHD cases and 69 controls, with three of them, miR-26b-5p, miR-185-5p, and miR-191-5p, being highly predictive for diagnostic status in an independent dataset of 44 ADHD cases and 46 controls. Investigation of downstream microRNA-mediated mechanisms underlying the disorder, which was focused on differentially expressed, experimentally validated target genes of the three highly predictive microRNAs, provided evidence for aberrant myo-inositol signaling in ADHD and indicated an enrichment of genes involved in neurological disease and psychological disorders. Our comprehensive study design reveals novel microRNA-mRNA expression profiles aberrant in ADHD, provides novel insights into microRNA-mediated mechanisms contributing to the disorder, and highlights promising candidate peripheral biomarkers.

Integrative genomic analysis of methylphenidate response in attention-deficit/hyperactivity disorder.

Methylphenidate (MPH) is the most frequently used pharmacological treatment in children with attention-deficit/hyperactivity disorder (ADHD). However, a considerable interindividual variability exists in clinical outcome. Thus, we performed a genome-wide association study of MPH efficacy in 173 ADHD paediatric patients. Although no variant reached genome-wide significance, the set of genes containing single-nucleotide polymorphisms (SNPs) nominally associated with MPH response (P < 0.05) was significantly enriched for candidates previously studied in ADHD or treatment outcome. We prioritised the nominally significant SNPs by functional annotation and expression quantitative trait loci (eQTL) analysis in human brain, and we identified 33 SNPs tagging cis-eQTL in 32 different loci (referred to as eSNPs and eGenes, respectively). Pathway enrichment analyses revealed an over-representation of genes involved in nervous system development and function among the eGenes. Categories related to neurological diseases, psychological disorders and behaviour were also significantly enriched. We subsequently meta-analysed the association with clinical outcome for the 33 eSNPs across the discovery sample and an independent cohort of 189 ADHD adult patients (target sample) and we detected 15 suggestive signals. Following this comprehensive strategy, our results provide a better understanding of the molecular mechanisms implicated in MPH treatment effects and suggest promising candidates that may encourage future studies.

Gene-wide Association Study Reveals RNF122 Ubiquitin Ligase as a Novel Susceptibility Gene for Attention Deficit Hyperactivity Disorder.

Attention Deficit Hyperactivity Disorder (ADHD) is a common childhood-onset neurodevelopmental condition characterized by pervasive impairment of attention, hyperactivity, and/or impulsivity that can persist into adulthood. The aetiology of ADHD is complex and multifactorial and, despite the wealth of evidence for its high heritability, genetic studies have provided modest evidence for the involvement of specific genes and have failed to identify consistent and replicable results. Due to the lack of robust findings, we performed gene-wide and pathway enrichment analyses using pre-existing GWAS data from 607 persistent ADHD subjects and 584 controls, produced by our group. Subsequently, expression profiles of genes surpassing a follow-up threshold of P-value < 1e-03 in the gene-wide analyses were tested in peripheral blood mononucleated cells (PBMCs) of 45 medication-naive adults with ADHD and 39 healthy unrelated controls. We found preliminary evidence for genetic association between RNF122 and ADHD and for its overexpression in adults with ADHD. RNF122 encodes for an E3 ubiquitin ligase involved in the proteasome-mediated processing, trafficking, and degradation of proteins that acts as an essential mediator of the substrate specificity of ubiquitin ligation. Thus, our findings support previous data that place the ubiquitin-proteasome system as a promising candidate for its involvement in the aetiology of ADHD.

Dopamine receptor DRD4 gene and stressful life events in persistent attention deficit hyperactivity disorder.

We performed a case-control association study in persistent ADHD considering eight candidate genes (DRD4, DAT1/SLC6A3, COMT, ADRA2A, CES1, CYP2D6, LPHN3, and OPRM1) and found additional evidence for the involvement of the Dup 120bp and VNTR 48bp functional variants within the dopamine receptor DRD4 gene in the etiology of adult ADHD. We subsequently investigated the interaction of stressful life events with these two DRD4 polymorphisms, and the impact of such events on the severity of ADHD symptomatology. The gene-by-environment analysis revealed an independent effect of stressful experiences on the severity of persistent ADHD, and a gene-by-environment interaction on the inattentive dimension of the disorder, where non carriers of the Dup 120bp (L) - VNTR 48bp (7R) haplotype were more sensitive to environmental adversity than carriers. These results are in agreement with previous works reporting a relationship between DRD4 and the effect of adverse experiences, which may explain the discordant findings in previous genetic studies and strengthen the importance of gene-by-environment interactions on the severity of ADHD. © 2015 Wiley Periodicals, Inc.

Case-control genome-wide association study of persistent attention-deficit hyperactivity disorder identifies FBXO33 as a novel susceptibility gene for the disorder.

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder with high heritability. At least 30% of patients diagnosed in childhood continue to suffer from ADHD during adulthood and genetic risk factors may play an essential role in the persistence of the disorder throughout lifespan. To date, genome-wide association studies (GWAS) of ADHD have been completed in seven independent datasets, six of which were pediatric samples and one on persistent ADHD using a DNA-pooling strategy, but none of them reported genome-wide significant associations. In an attempt to unravel novel genes for the persistence of ADHD into adulthood, we conducted the first two-stage GWAS in adults with ADHD. The discovery sample included 607 ADHD cases and 584 controls. Top signals were subsequently tested for replication in three independent follow-up samples of 2104 ADHD patients and 1901 controls. None of the findings exceeded the genome-wide threshold for significance (PGC<5e-08), but we found evidence for the involvement of the FBXO33 (F-box only protein 33) gene in combined ADHD in the discovery sample (P=9.02e-07) and in the joint analysis of both stages (P=9.7e-03). Additional evidence for a FBXO33 role in ADHD was found through gene-wise and pathway enrichment analyses in our genomic study. Risk alleles were associated with lower FBXO33 expression in lymphoblastoid cell lines and with reduced frontal gray matter volume in a sample of 1300 adult subjects. Our findings point for the first time at the ubiquitination machinery as a new disease mechanism for adult ADHD and establish a rationale for searching for additional risk variants in ubiquitination-related genes.

The effect of age on DNA concentration from whole saliva: implications for the standard isolation method.

OBJECTIVES: Adequate quantity and quality of the DNA isolated from saliva samples are crucial for ensuring successful genotyping rates in genetic studies. However, there is little information about these issues when saliva samples are collected from children. The objectives of this study were to assess whether there are differences in DNA quality or quantity isolated from saliva samples of children at different ages and adolescents compared to adults and, if so, to establish a modified protocol to improve and standardize DNA isolation from saliva samples of children. METHODS: Saliva samples were collected with Oragene DNA Sample Collection Kit from 41 healthy subjects including children of different ages, adolescents, and adults. Quantity and quality of isolated DNA were determined spectrophotometrically. RESULTS: DNA concentration and age were positively correlated (r = 0.676, P < 0.001). A high percentage of samples from children below 12 years yielded DNA concentrations <100 ng/µL and DNA quality a260/a280 ratios of <1.8. Modifying the standard DNA isolation method raised DNA quantity and quality in these critical samples. CONCLUSIONS: Age determines, at least in part, the high variability observed in the concentration of DNA isolated from saliva samples. This fact should be taken into account for a better standardization of the DNA isolation to ensure DNA banking in large-scale genetic studies involving children.