FAM57B is a modulator of ceramide synthesis that regulates sphingolipid homeostasis and synaptic composition in the developing brain

The complex 16p11.2 Deletion Syndrome (16pdel) is accompanied by neurological disorders, including epilepsy, autism spectrum disorder and intellectual disability. We demonstrate that 16pdel iPSC differentiated neurons showed augmented local field potential activity and altered ceramide-related lipid species relative to unaffected. FAM57B , a poorly characterized gene in the 16p11.2 interval, has emerged as a candidate tied to symptomatology. We found that FAM57B modulates ceramide synthase (CerS) activity, but is not a CerS per se. In FAM57B mutant human neuronal cells and zebrafish brain, composition and levels of sphingolipids and glycerolipids associated with cellular membranes are disrupted. Consistently, we observed aberrant plasma membrane architecture and synaptic protein mislocalization, which were accompanied by depressed brain and behavioral activity. Together, these results suggest that haploinsufficiency of FAM57B contributes to changes in neuronal activity and function in 16pdel Syndrome, through a crucial role for the gene in lipid metabolism. ### Competing Interest Statement The authors have declared no competing interest.