Posted in Web STM | definition of STM by Medical dictionary December 1, 2019 STM: A gene on chromosome 16p11.2 that encodes a sulfotransferase which sulfonates and activates phenolic monoamines (e.g., neurotransmitters dopamine, norepinephrine and serotonin), as well as phenolic and catechol drugs. https://medical-dictionary.thefreedictionary.com/STM