What are the genetic changes related to sepiapterin reductase deficiency ?
Mutations in the SPR gene cause sepiapterin reductase deficiency. The SPR gene provides instructions for making the sepiapterin reductase enzyme. This enzyme is involved in the production of a molecule called tetrahydrobiopterin (also known as BH4). Specifically, sepiapterin reductase is responsible for the last step in the production of tetrahydrobiopterin. Tetrahydrobiopterin helps process several building blocks of proteins (amino acids), and is involved in the production of chemicals called neurotransmitters, which transmit signals between nerve cells in the brain.  SPR gene mutations disrupt the production of sepiapterin reductase. Most SPR gene mutations result in an enzyme with little or no function. A nonfunctional sepiapterin reductase leads to a lack of tetrahydrobiopterin. In most parts of the body, there are alternate pathways that do not use sepiapterin reductase for the production of tetrahydrobiopterin, but these pathways are not found in the brain. Therefore, people with sepiapterin reductase deficiency have a lack of tetrahydrobiopterin in the brain. When no tetrahydrobiopterin is produced in the brain, production of dopamine and serotonin is greatly reduced. Among their many functions, dopamine transmits signals within the brain to produce smooth physical movements, and serotonin regulates mood, emotion, sleep, and appetite. The lack of these two neurotransmitters causes the problems with movement and other features of sepiapterin reductase deficiency.