Visual impairment is not an early symptom in CLN2, and VEP may be absent.17, 38When present, increased latency is the most common pattern in CLN2, present in up to 50% of patients.17, 38An electroretinogram is challenging to carry out in children, and it is subject to errors from the examiner (consensus; LE: 5). The gene discussed is TPP1; the disease is Visual impairment.