5-Hydroxymethylcytosine was observed by Skirmantas Kriaucionis, an associate at the Heintz lab, who was looking for levels of 5-methylcytosine in two different neuron types. He discovered a significant amount of an unknown substance instead, and after conducting several tests, identified it as being 5-hydroxymethylcytosine.A, T, G, C and What?, popsci.com
