Dimensional phenotype measurement in children with rare genetic conditions: new insights into the aetiology of neurodevelopmental and psychiatric disorders.

Rare neurodevelopmental genetic conditions (NGCs) present with diverse and complex phenotypic manifestations, often resulting in a range of clinical and cognitive difficulties that cut across traditional, categorically defined neurodevelopmental and neuropsychiatric diagnoses. Traditional categorical diagnostic frameworks have significant limitations in capturing the full complexity and heterogeneity of these phenotypes. This perspective reviews current advances in the field, highlighting the benefits of dimensional frameworks like the Research Domain Criteria (RDoC) and the Hierarchical Taxonomy of Psychopathology (HiTOP). Dimensional approaches have shown promise in capturing subthreshold symptoms and behavioural dimensions predictive of later neuropsychiatric outcomes. The transition to dimensional frameworks offers significant potential for improving diagnostic accuracy and informing personalised treatment strategies. However, the field remains hindered by the lack of standardised and validated dimensional assessment tools. Future research should focus on developing new assessment tools that are specifically designed for NGCs and are culturally and neurodivergence sensitive, with researchers, clinicians, and families codeveloping measures to ensure the practical application of these tools.