SYP and obesity due to melanocortin 4 receptor deficiency: However, circDennd1b knockdown significantly decreased the expression of Stx1a and Syp in Chol-treated neurons without affecting its host gene expression (Figure 4D and Figure S13D), indicating that circDennd1b has a distinct role depending on obesity-related serum factors and is involved in the formation of synaptic vesicles and density in Chol-treated neurons.