Serotonin is a monoamine neurotransmitter synthesized in the CNS. It is an important modulator of sleep, body temperature and metabolism. Guanosine triphosphate cyclohydrolase I (GCH1) catalyzes the production of Tetrahydrobiopterin (BH4), a required cofactor in the conversion of L-tryptophan to 5-hydroxytryptophan which is then converted to serotonin. Serotonin is released at the synapse of the presynaptic neuron where it binds to its receptor on the postsynaptic neuron....