The Behavioral Phenotype of 47,XYY Syndrome: An Integrative Review of Neuropsychological, Psychosocial, and Developmental Trajectories

Abstract

47,XYY syndrome, a sex chromosome aneuploidy (SCA) affecting approximately 1 in 1,000 male births, has been historically shrouded in controversy due to early, flawed studies linking the karyotype directly to aggression and criminality. Modern research has dispelled these simplistic and stigmatizing notions, revealing a more complex and nuanced behavioral phenotype. This paper provides a comprehensive review of the current scientific understanding of the behavioral profile associated with 47,XYY. We synthesize evidence indicating that the core challenges in this population lie not in heightened aggression, but in vulnerabilities across neurodevelopmental domains. These include an increased risk for developmental delays, particularly in speech and language, leading to a high prevalence of language-based learning disabilities. Executive function deficits, including impairments in working memory, cognitive flexibility, and inhibitory control, are common and represent a primary mediator of behavioral outcomes. Furthermore, individuals with 47,XYY exhibit a significantly elevated risk for traits associated with Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD), which profoundly impact social functioning and academic achievement. Emerging neurobiological evidence points to gene dosage effects of Y-chromosome genes and altered neurodevelopment as key underpinnings of this phenotype. Psychosocially, these neurocognitive challenges can manifest as impulsivity, emotional dysregulation, and social immaturity, often misinterpreted as intentional volitional aggression. This review underscores the critical role of early diagnosis, multidisciplinary intervention, and a shift in perspective from a behavioral-deficit model to a neurodevelopmental vulnerability model. By understanding the biological and cognitive underpinnings of these behaviors, clinicians, educators, and families can better support the developmental trajectories of individuals with 47,XYY syndrome, fostering improved adaptive outcomes and quality of life.