This gene encodes a member of the biopterin-dependent aromatic amino acid hydroxylase family. The encoded protein is one of two tryptophan hydroxylase enzymes that catalyze the first and rate limiting step in the biosynthesis of the hormone and neurotransmitter, serotonin. This gene is expressed in peripheral organs, while tryptophan hydroxylase 2 is expressed in neurons. The encoded protein is involved in the development of hypoxia-induced elevations in pulmonary pressures and pulmonary vascular remodeling, and has also been implicated as a regulator of immune tolerance. Disruption of this gene is associated with cardiac dysfunction. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Feb 2013]