Two closely related viruses, coxsackievirus A16 (CA16) and enterovirus 71 (EV71), which belong to the Enterovirus genus of the Picornavirus family, and usually co-circulate during HFMD outbreaks [1]–[3], have been identified as the most frequent pathogens of HFMD, and other enteroviruses, including CA2, CA4, CA5, CA7, CA9, CA10, CA16, CB1, CB2, CB3, CB4 and CB5 can also cause HFMD. The gene discussed is CA4; the disease is hand, foot and mouth disease.