(A) EM analysis of cortical synapses derived from WT and MPS-IIIA mice at different ages. The size of synaptic vesicles was quantified from 400-500 vesicles (taken from 5 mice for each genotype at each time point) and expressed as the average of vesicle diameter (nm). The number of synaptic vesicles per synapse was quantified from 20 different images (taken from 5 mice for each genotype at each time point), normalized by the length of synaptic cleft and expressed as % of WT. The synaptic density was measured from 20 different images (taken from 5 mice for each genotype at each time point) as the number of synapses/area(#/500μm2) and expressed as % of WT.Arrows indicate the synaptic cleft, while asterisks indicate abnormal vacuoles 