MFSD2A and Allan-Herndon-Dudley syndrome: Owing to the crucial role of Mfsd2a in transporting essential fatty acids and promoting BBB formation and brain development, Mfsd2a knockout induces microcephaly, Allan-Herndon-Dudley syndrome, and other severe side effects (e.g., BBB breakdown, neuronal loss, cognitive impairment, intellectual disability, behavioral deficits, spasticity, and absent speech and so on) [4,121,127,128,130,131,132].