Seizure onset mainly occurred in the neonatal period (67.8% of cases), while only ten patients presented with seizures after the age of 12 months (four with ALDH7A1 deficiency, three with PNPO deficiency, one with PLPBL, and two with hyperprolinemia type II) (Table 2, Supplementary File S1). Here, PNPO is linked to hyperprolinemia type 2.