SCN2B, SCN3B and SCN4B are syntenic with each other and with EVA1, EVA-1L , and APOA-1 in multiple vertebrate genomes, while SCN1B is syntenic with FBL and PSMC4 in humans, rats, and zebrafish. To analyze synteny, β subunits and subunit-like genes were identified in human, rat, zebrafish, frog and bird genomes (see Table 7 for gene IDs and physical locations). While humans and rats have four and zebrafish have five β subunit genes, only three β subunit genes were identified in frogs and birds (β1 was not found in either genome). Reciprocal blast searches and in silico chromosome walking were used to assess physical relationships among vertebrate β subunit-like genes. HUGO gene nomenclature symbol IDs: PSMC4 = 26S protease regulatory subunit 6B; FBL = fibrillarin; APOA1 = apolipoprotein A-1; MPZ = myelin protein zero; MPZL1 = myelin protein zero-like gene, isoform A; EVA1 = epithelial V-like antigen 1; EVA1L = unannotated gene similar to EVA1. Red = β subunit genes, Blue = β subunit-like genes, Black = unrelated genes that are syntenic with β subunits.