SMPD1 and schizophrenia: For four key sphingolipid regulatory genes involved in cognitive and emotional behavioral regulation [50, 51], the major two related to ceramide synthesis (SMPD1 and SMPD3) and major two related to ceramide metabolism (ASAH1 and ASAH2), we extracted single-nucleotide polymorphisms (SNPs) that cover a gene region (extended to ± 10 KB) and their association with schizophrenia from the latest genome-wide association study (GWAS) summary statistics of wave 3 Psychiatric Genomics Consortium (PGC) GWAS of schizophrenia.