Age-related differences in Intelligence, Executive Functions and Behaviours - across Childhood and Adolescence in boys with Duchenne Muscular Dystrophy

Abstract

Gillenstrand, J. (2026). Age-related differences in Intelligence, Executive Functions and Behaviours - across Childhood and Adolescence in boys with Duchenne Muscular Dystrophy. Department of Psychology, University of Gothenburg, Sweden. Duchenne Muscular Dystrophy (DMD) is a severe X-linked disorder caused by mutations in the DMD gene, resulting in the absence of dystrophin, a protein essential for muscle function and brain development. In addition to progressive muscle degeneration, DMD is associated with neuropsychological difficulties affecting intelligence, executive functions (EF), and behaviour. These challenges emerge across development and may affect both the child and the family system. This thesis examines age-related differences in intelligence, EF, and behaviour in boys with DMD from childhood to adolescence. The Developmental Systems Approach (DSA) served as the theoretical framework, emphasizing interactions between child characteristics, family resources, and family functioning. An updated DSA model is proposed that incorporates the progressive nature of DMD and the adaptive demands placed on boys and their families. Seventy-three boys with DMD and their families participated in assessments at ages 5, 8, 11, and 14 years. Longitudinal data were available for 13 boys assessed between ages 5–8, 8–11, or 11–14 years. Study I investigated behavioural strengths and difficulties in relation to intellectual functioning and age. Full-Scale IQ (FSIQ) and Working Memory Index (WMI) scores were approximately one standard deviation below age norms. Verbal abilities remained relatively stable, whereas FSIQ differed between younger and older boys. Behavioural difficulties were most pronounced at ages 8 and 11 and were associated with working memory, motor functioning, and family socioeconomic status. Study II examined the relationship between performance-based EF measures and parent- and self-ratings of EF. No significant concordance was found, suggesting that these methods capture different aspects of EF. Performance-based measures primarily reflected “cold” EF, whereas ratings reflected “hot” EF involving emotional and motivational regulation. Difficulties were evident in both domains. Parental life satisfaction and maternal carrier status were associated with parental ratings of EF. Study III explored age-related differences in hot and cold EF. Results indicated developmental patterns, suggesting that hot EF may diverge from typical development earlier than cold EF. Overall, the findings demonstrate that intelligence, EF, and behaviour are affected in boys with DMD and that vulnerabilities vary across development. The results highlight the importance of understanding neuro-psychological functioning within a developmental and family context and underscore the need for interventions that support both boys with DMD and their families.