Synaptotagmin-1 (SYT1) is a presynaptic vesicular protein which plays a crucial role in triggering synchronous neurotransmitter release. It is comprised of two key domains: the C2B domain, which requisitely binds intracellular calcium to facilitate vesicular fusion; and the C2A domain, which plays an auxiliary role in evoked exocytosis. Pathogenic C2B domain variants cause SYT1-associated neurodevelopmental disorder, a rare condition characterised by movement disorder, developmental delay and intellectual disability. Recently, a number of new pathogenic SYT1 variants have been identified. These have included the first disease-associated C2A domain variants, which result in milder disease phenotypes, as well as additional C2B domain variants. These discoveries have broadened the phenotypic spectrum of SYT1-associated neurodevelopmental disorder. Several C2B domain variants were previously shown to slow synaptic vesicle exocytosis. However, it was unclear whether the newly-identified variants – particularly the C2A domain variants – would share this pathogenic mechanism. Here, we investigate the effects of four novel C2A domain and four novel C2B domain variants on SYT1 function in primary hippocampal neuronal cultures. We demonstrate that both C2A and C2B domain variants slow synaptic vesicle exocytosis, but they do so in a graded manner, with C2A domain variants having a milder effect than C2B domain variants. Furthermore, the severity of exocytic defects induced by SYT1 variants strongly correlates with the severity of impairment in motor and communication abilities seen clinically in patients harbouring each variant. Together, these data suggest that exocytic defects may underpin key phenotypic features observed in patients with SYT1-associated neurodevelopmental disorder.