Executive Functions in Girls with ADHD Followed Prospectively into Young Adulthood

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent and impairing neurodevelopmental disorder characterized by developmentally extreme levels of (a) hyperactivity-impulsivity and/or (b) inattention-disorganization (American Psychiatric Association, 2000). A large number of studies have documented neuropsychological deficits in individuals with ADHD, particularly within the executive function (EF) domain (e.g., Berlin, Bohlin, & Rydell, 2003; Scheres et al., 2004; Thorell, 2007). These deficits have been found across multiple studies of children and adolescents with ADHD (e.g., Rapport, Alderson, Kofler, Sarver, Bolden, & Sims, 2008; Re, De Franchis, & Cornoldi, 2010; for a review, see Martinussen, Hayden, Hogg-Johnson, & Tannock, 2005), as well as adults with ADHD (e.g., Rohlf et al., 2011; for a review, see Boonstra, Oosterlaan, Sergeant, & Buitelaar, 2005). Although there is some debate over exactly which abilities constitute the construct of EF, it is generally conceptualized as an umbrella term that encompasses skills such as planning, organization, response inhibition, sustained attention, set shifting, working memory, and reasoning. Performance of these EFs appears to rely on the prefrontal cortex and its extensive interconnections with other brain regions (Tranel, Anderson, & Benton, 1994). Recent studies have focused on the ability of EF to predict functioning in multiple domains. That is, EFs have been linked to academic performance (Barry, Lyman, & Klinger, 2002; Biederman et al., 2004; Miller & Hinshaw, 2010), social/interpersonal skills (Clark et al., 2002; Diamantopoulou et al., 2007; Gilotty, Kenworthy, Sirian, Black, & Wagner, 2002; Miller & Hinshaw, 2010; Rinsky & Hinshaw, 2011), occupational functioning (Barkley & Fischer, 2011), and global functioning (Miller & Hinshaw, 2010). Recent examination of the present sample indicated that EF abilities in childhood are predictive of academic and occupational functioning in young adulthood (Miller, Nevado, & Hinshaw, 2011). Thus, EFs appear to be implicated in the performance of critical cross-domain abilities. Several issues are relevant when studying EF impairments in ADHD. First, although deficits in EF are common in ADHD, such deficits do not characterize all individuals with this disorder (Biederman et al., 2004; Nigg, Willcutt, Doyle, & Sonuga-Barke, 2005), and those with EF impairment may constitute a distinct subgroup (Lambek et al., 2010; Nigg et al., 2005). Second, these types of deficits are not unique to ADHD. Indeed, EF deficits have been found across multiple neurodevelopmental disorders (for a classic review, see Pennington & Ozonoff, 1996). Third, there is question as to whether the subtypes of ADHD–Predominantly Inattentive type versus Combined (or Hyperactive-Impulsive) show differential EF deficits. These subtypes, which have been posited to comprise distinct entities (see Milich, Balantine, & Lynam, 2001), have not consistently yielded neuropsychological or EF differences (e.g., Geurts, Verte, Oosterlaan, Roeyers, & Sergeant, 2005; Hinshaw, Carte, Fan, Jassy, & Owens, 2007; Hinshaw, Carte, Sami, Treuting, & Zupan, 2002; O'Brien et al., 2010; Pasini, Paloscia, Alessandrelli, Porfirio, & Curatolo, 2007). In short, although EF deficits are not found in all individuals with ADHD, nor are they specific to ADHD, they have consistently been shown to be of critical importance by predicting impairment across a range of domains of functioning and could constitute a treatment target in those who do exhibit impairment. Despite an increased focus on girls with ADHD in the past decade (see Hinshaw & Blachman, 2005), there is still a large gap in our knowledge about the presentation and course of ADHD in females, particularly in those followed prospectively. In terms of EF, studies have shown girls with ADHD to be impaired relative to age-matched female controls (Castellanos et al., 2000; Hinshaw et al., 2002; Seidman et al., 2005) and at least as impaired as boys with ADHD (O'Brien et al., 2010; Seidman et al., 2005). Longitudinal investigations of girls with ADHD have shown that these deficits appear to persist over time. Hinshaw et al. (2007) followed a sample of carefully ascertained girls ages 6-12 into adolescence and found that those with childhood-diagnosed ADHD continued to exhibit EF impairment in adolescence. Similarly, Biederman et al. (2008) followed sample of girls ages 6-17 over 5 years and found that girls with ADHD showed continued impairment in neuropsychological functioning at follow-up, with the exception of set shifting. Thus, although it is now apparent that deficits in EF persist into adolescence in at least some childhood-diagnosed girls with ADHD, it is unknown whether such impairments continue to be present in young adulthood. The transition to young adulthood is known to be a time of critical importance and increased demands (see Arnett, 2000), yet few studies have followed cohorts of girls with ADHD into emerging adulthood. Although the extant literature is limited, it is quite clear that cross-domain impairment persists into late adolescence and young adulthood in childhood-diagnosed girls with ADHD. Such continued impairment extends across multiple domains including ADHD symptoms, academic functioning, comorbid psychopathology, occupational functioning, and romantic and family relationships (Babinski et al., 2011; Biederman et al., 2010; Chronis-Tuscano et al., 2010; Hinshaw et al., 2011; Mick et al., 2011). However, no investigations to our knowledge have reported on the possibility of continuing EF impairments in young adulthood. Thus, we aim to examine whether deficits in EF persist into young adulthood in females with ADHD. Our team collected EF data on a large, well-characterized, and diverse sample of preadolescent girls with ADHD and a matched comparison sample, ages 6-12 years. In childhood, the ADHD group showed clear EF deficits relative to the comparison group with stringent statistical control of demographic variables, comorbid disorders, and Full-Scale IQ (FSIQ). Comparisons between ADHD-Combined (ADHD-C) and ADHD-Inattentive (ADHD-I) subtypes were rarely significant (Hinshaw et al., 2002). This sample was then followed prospectively into adolescence with similar findings. Specifically, the childhood-defined ADHD group again showed clear EF deficits relative to comparisons under statistical control of demographic variables and comorbid disorders (but not with the addition of FSIQ); subtype differences were again minimal (Hinshaw et al., 2007). When examining EF abilities using adolescent diagnostic status (ADHD-C, ADHD-I, and no ADHD), EF deficits emerged in the ADHD groups with full statistical control, including IQ as a covariate. At the present 10-year follow-up, parallel to our previous reports in childhood and adolescence, we aim to determine (a) whether preadolescent girls with ADHD continue to show EF impairment in young adulthood, relative to a matched comparison group; (b) whether such deficits are robust to statistical control of age, socioeconomic status, maternal education, comorbidities, and full-scale intelligence yielded from baseline measures during childhood; and (c) whether the girls who continue to meet diagnostic criteria for ADHD at follow-up show particularly strong EF deficits in young adulthood. Our main hypotheses are as follows: (1) EF deficits will persist through young adulthood for the participants with ADHD; (2) they will be robust to statistical control of demographics, comorbidities, and IQ; and (3) participants meeting criteria for ADHD in young adulthood will show the largest degree of EF impairment at follow-up. We also predict that ADHD-C and ADHD-I differences will continue to be small.