This study evaluates the long-term clinical and developmental outcomes of individuals with SCN1A-positive Dravet syndrome over a 10-year period. The research, conducted in the UK from 2010 to 2020, followed 113 patients and their caregivers, with 68 caregivers returning questionnaires. Key findings include: - **Developmental Outcomes**: Developmental outcomes worsened over time, with profound cognitive impairment observed at follow-up compared to moderate cognitive impairment at baseline (P < 0.001). Epilepsy severity appeared less severe at 10 years (P = 0.042). - **Comorbidities**: An increase in comorbidities such as autistic features (77% vs. 30%, χ² = 19.9, P < 0.001), behavioural problems (81% vs. 38%, χ² = 14.1, P < 0.001), and motor/mobility problems (80% vs. 41%, χ² = 16.9, P < 0.001) was noted. - **Predictors of Poor Outcomes**: Poor baseline language ability (P < 0.001), more severe baseline epilepsy severity (P = 0.003), and a worse SCN1A genetic score (P = 0.027) were significant predictors of worse long-term developmental outcomes. - **Sudden Unexpected Death in Epilepsy (SUDEP)**: 35% of participants had not discussed SUDEP with a medical professional. - **Caregiver Burden**: Over 90% of caregivers reported negative impacts on their health and career opportunities. The study highlights the importance of early and focused therapies, the role of the SCN1A genetic score as a potential biomarker, and the need for better access to additional therapies and support for caregivers.This study evaluates the long-term clinical and developmental outcomes of individuals with SCN1A-positive Dravet syndrome over a 10-year period. The research, conducted in the UK from 2010 to 2020, followed 113 patients and their caregivers, with 68 caregivers returning questionnaires. Key findings include: - **Developmental Outcomes**: Developmental outcomes worsened over time, with profound cognitive impairment observed at follow-up compared to moderate cognitive impairment at baseline (P < 0.001). Epilepsy severity appeared less severe at 10 years (P = 0.042). - **Comorbidities**: An increase in comorbidities such as autistic features (77% vs. 30%, χ² = 19.9, P < 0.001), behavioural problems (81% vs. 38%, χ² = 14.1, P < 0.001), and motor/mobility problems (80% vs. 41%, χ² = 16.9, P < 0.001) was noted. - **Predictors of Poor Outcomes**: Poor baseline language ability (P < 0.001), more severe baseline epilepsy severity (P = 0.003), and a worse SCN1A genetic score (P = 0.027) were significant predictors of worse long-term developmental outcomes. - **Sudden Unexpected Death in Epilepsy (SUDEP)**: 35% of participants had not discussed SUDEP with a medical professional. - **Caregiver Burden**: Over 90% of caregivers reported negative impacts on their health and career opportunities. The study highlights the importance of early and focused therapies, the role of the SCN1A genetic score as a potential biomarker, and the need for better access to additional therapies and support for caregivers.