['Lafora disease (LD) is a fatal autosomal recessive neurodegenerative disease. A hallmark of LD is cytoplasmic accumulation of insoluble glucans, called Lafora bodies (LBs). Mutations in the gene encoding the phosphatase laforin account for approximately 50% of LD cases, and this gene is conserved in all vertebrates. We recently demonstrated that laforin is the founding member of a unique class of phosphatases that dephosphorylate glucans.', 'Herein, we identify laforin orthologs in a protist and two invertebrate genomes, and report that laforin is absent in the vast majority of protozoan genomes and it is lacking in all other invertebrate genomes sequenced to date. We biochemically characterized recombinant proteins from the sea anemone Nematostella vectensis and the amphioxus Branchiostoma floridae to demonstrate that they are laforin orthologs. We demonstrate that the laforin gene has a unique evolutionary lineage; it is conserved in all vertebrates, a subclass of protists that metabolize insoluble glucans resembling LBs, and two invertebrates. We analyzed the intron-exon boundaries of the laforin genes in each organism and determine, based on recently published reports describing rates of molecular evolution in Branchiostoma and Nematostella, that the conservation of laforin is linked to the molecular rate of evolution and the glucan metabolism of an organism.'] Is conservation of the glucan phosphatase laforin linked to rates of molecular evolution and the glucan metabolism of the organism?