Spinal manifestations of CLN1 disease start during the early postnatal period

Aim: To understand the progression of CLN1 disease and develop effective therapies we need to characterize early sites of pathology. Therefore, we performed a comprehensive evaluation of the nature and timing of early CLN1 disease pathology in the spinal cord, which appears especially vulnerable, and how this may affect behaviour. Methods: We measured the spinal volume and neuronal number, and quantified glial activation, lymphocyte infiltration and oligodendrocyte maturation, as well as cytokine profile analysis during the early stages of pathology in Ppt1-deficient (Ppt1^−/−) mouse spinal cords. We then performed quantitative gait analysis and open-field behaviour tests to investigate the behavioural correlates during this period. Results: We detected significant microglial activation in Ppt1^−/− spinal cords at 1 month. This was followed by astrocytosis, selective interneuron loss, altered spinal volumes and oligodendrocyte maturation at 2 months, before significant storage material accumulation and lymphocyte infiltration at 3 months. The same time course was apparent for inflammatory cytokine expression that was altered as early as one month. There was a transient early period at 2 months when Ppt1^−/− mice had a significantly altered gait that resembles the presentation in children with CLN1 disease. This occurred before an anticipated decline in overall locomotor performance across all ages. Conclusion: These data reveal disease onset 2 months (25% of life-span) earlier than expected, while spinal maturation is still ongoing. Our multi-disciplinary data provide new insights into the spatio-temporal staging of CLN1 pathogenesis during ongoing postnatal maturation, and highlight the need to deliver therapies during the presymptomatic period.