It is administered as an intracerebroventricular infusion every two weeks.5 The effect of ERT on functional decline can be measured using the CLN2 Disease Clinical Rating Scale (CLN2 CRS).6 Patients on ERT are less likely to have an unreversed two-point decline in a combined motor and language function score when compared to untreated patients.5 Currently the only way to monitor treatment is through the CLN2 CRS as there are no biomarkers used to monitor neurodegeneration. Here, TPP1 is linked to congenital rubella syndrome.