Answer: serotonin; glucocorticoid receptor gene
Step-by-step explanation:
Neurotransmitter serotonin, also known as serotonin is used in the body to send messages between nerve cells. It affects the human mood, appetite, and digestion, it also helps regular sleeping cycles in the body.
Glucocorticoid receptor gene is a receptor which binds the cortisol and other glucocorticoids. The glucocorticoid receptor gene regulates development of metabolism and immune system.
Howard's growing up condition would make him have decrease in Neurotransmitter serotonin(making him lacking appetite and moody most times) and an increase in Glucocorticoid receptor gene(having a dysfunctional growth pattern).