SYT1 and metachromatic leukodystrophy: The delayed expression of β-tubulin III (compare ND and MLD at d0-d14; Fig. 3a, b) and the reduced expression of synaptotagmin 1 (a protein involved in neurotransmission) at d24 and d34 (Fig. 3c) further suggested impaired differentiation of MLD neurons.