CCL21 and neurodevelopmental disorder: Solute carriers, or SLCs, are the most prominent family of transmembrane transporters responsible for the diffusion of nutrients, ions, metabolites, and drugs across cell membranes [45, 46] About 287 SLC genes are present in the human brain, and mutations or the resulting dysfunctions of 71 SLC genes have been linked to various neurodevelopmental disorders [47].