Cognitive and behavioral indicators of ADHD symptoms prior to school age

Attention Deficit Hyperactivity Disorder (ADHD) is one of the most common developmental disorders, affecting an estimated 9.5 percent of school age children and adolescents (Visser, Bitsko, Danielson, Perou, & Blumberg, 2010). Symptoms of ADHD have been shown to have a major impact on social functioning (Mannuzza, Klein, Bessler, Malloy, & LaPadula, 1993) and are frequently comorbid with other psychopathology, such as social and emotional disorders, learning disabilities, and conduct disorder (Pennington, 2002). Genetic markers, male gender, prenatal toxin exposure, and early environmental experiences have all been identified as risk factors for ADHD, suggesting early and stable etiology (Pennington, 2002). Despite evidence for early causal factors, ADHD is identified by school teachers more often than by parents or physicians, indicating that diagnoses are unlikely to occur prior to entrance into a formal school setting (Sax & Kautz, 2003). This limits opportunities for early interventions that could potentially minimize academic and social-emotional impairment associated with ADHD symptomology. The current study aims to identify behavioral and cognitive correlates of later ADHD symptoms that are present prior to school age, examine symptom differences across genders, and clarify the developmental trajectories of comorbid symptoms across childhood. Friedman, Watamura, and Robertson (2005) found a unique association between movement suppression in infancy and parent-report of the same children’s inattentive symptoms at school age (range: r= −0.56 to r= −0.69). Behavioral correlates prior to preschool include temperament and regulatory disturbances, such as increased irritability, crying, hyperactivity, and sleep problems (Goldsmith, 2004; Rao 2004; Wolke 2002; Thunstrom, 2002; Auerbach, et al., 2008). Although these results strongly suggest early behavioral and cognitive markers of ADHD the studies were limited by the use of small, male-only, and/or clinical samples, and outcomes measured prior to school age using non-DSM-IV-TR criteria. Concurrent comorbid psychopathology in ADHD is also common. Comorbid features during school age and adolescence include externalizing and internalizing symptoms (Larsson, Dilshad, Lichtenstein, & Barker, 2011; Wilens et al., 2002; Willcutt, Pennington, Chhabildas, Friedman, & Alexander, 1999), social difficulties (DuPaul, McGoey, Eckert, & VanBrakle, 2001; Wilens et al., 2002), sleep problems (Owens, 2005), learning disorders (Pennington, 2002; Spencer, Biederman, & Mick, 2007), low IQ (Kuntsi et al., 2004) and poor academic achievement (Barkley, Anastopoulos, Guevremont, & Fletcher, 1991; Massetti et al., 2008). ADHD symptom dimensions (i.e. inattention and hyperactivity/impulsivity) show distinct patterns across development, with hyperactivity/impulsivity decreasing across childhood and adolescence, and inattention increasing or remaining stable (Larsson et al., 2011). Importantly, both symptom dimensions exhibit stability from childhood to adolescence. Given the prevalence of comorbidity in youth with ADHD, a logical question is whether comorbid symptoms also show distinct developmental trajectories across childhood and adolescence. The current study aims to examine change in common comorbid symptoms across development, as well as examine their predictive validity prior to school age. Diagnoses of ADHD typically include parent- and teacher-reports of children’s observable behaviors; questionnaires tend to target deficits in behaviors that are desirable in school age children (e.g. “makes careless mistakes in schoolwork”). Moreover, these diagnostic tools have typically been available in a single version for a wide variety of age groups, implying homotypic continuity of ADHD symptoms across development. However, literature suggests that ADHD is more likely a heterotypic developmental disorder; in other words, it may be manifested as different behaviors across the lifespan (Willoughby, 2003). Diagnostic screening tools that have been adapted to evaluate ADHD risk in preschool children are scarce, and those that do exist do not have data to support predictive validity for later ADHD diagnosis (Carter, Briggs-Gowan, Jones, & Little, 2003; Davis, Burns, Snyder, & Robinson, 2007; Gopin, Healey, Castelli, Marks, & Halperin, 2010; McGoey, DuPaul, Haley, & Shelton, 2007). A recent review of measures used to identify attention problems in preschool concluded that evidence informing the validity and utility of these measures remains limited (Mahone & Schneider, 2012). In contrast, early accurate screening exists for many childhood medical disorders such as phenylketonuria (PKU) and diabetes, the results of which facilitate early implementation of effective interventions. Similar efforts have been made in the field of child psychopathology to identify early markers of autism spectrum disorder (Ozonoff et al., 2008; Robins, Fein, Baron, & Green, 2001), reading disorder (Puolakanaho et al., 2007) and emotional disorders (Briggs-Gowan & Carter, 2008), among others. Both clinical and basic science stand to gain from the identification of early cognitive and behavioral markers of later ADHD symptomology. Importantly, females and males with ADHD are characterized by different prevalence rates and different comorbidity patterns. The male to female ratio is about 2:1 (Ramtekkar, Reiersen, Todorov, & Todd, 2010). A comprehensive meta-analysis reported that, on average, females with ADHD had lower ratings on hyperactivity, inattention, impulsivity, and externalizing problems and had greater intellectual impairments and more internalizing problems compared to males with ADHD (Gershon, 2002). In a population-based cohort of 11-year-olds, girls with ADHD appeared to be more negatively affected in academics and peer relationships than boys with ADHD (Elkins, Malone, Keyes, Iacono, & McGue, 2011). Moreover, girls with inattentive difficulties were more likely to be bullied. Gender differences also appear to vary as a function of age, with more severe inattention in boys during childhood, in girls during adolescence, and comparable across genders during adulthood (Kan et al., 2012). Clearly, both development and gender must be considered when examining characteristics of ADHD. The goals of the current study were threefold. First, we aimed to test the predictive power of very early, easily measured cognitive and behavioral measures in children who had high-ADHD symptom counts in third grade. Next, we examined sex differences in these early predictors. Finally, we examined the longitudinal patterns of predictive variance for well-known social-emotional and academic correlates of ADHD in order to test our hypothesis that the predictive power for these comorbid symptom clusters improves across childhood, with an obvious maximum at the time of high- versus low-ADHD categorization.