NTRK1 and anhidrosis: Surprisingly, our review also captured studies using HMA animal models of genetic disorders, such as Prader–Willi syndrome (genomic imprinting disorder), to test the role of the colon microbiota in metabolic complications [21, 22] and in congenital insensitivity to pain with anhidrosis (disease caused by pathogenic variants in the NTRK1 gene) to examine the effects of the gut microbiota on pain thresholds and behavior [23].