Neopterin, CSF

CSF Neopterin is useful for diagnosis of certain disorders of neurotransmitter metabolism. Neopterin is also useful as a marker for immune system stimulation. This testing may also be used for assessment of Variants of Uncertain Significance (VUS) identified during genetic testing (e.g. Next Generation Sequencing or Capillary Sequencing Testing). Tetrahydrobiopterin (BH4) serves as a cofactor for the hydroxylation of phenylalanine and in the biosynthesis of biogenic amines. Deficiency of BH4 may occur as a result of mutations causing a reduction in one of the three biosynthetic enzymes, guanosine triphosphate cyclohydrolase, 6-pyruvoyl-tetrahydropterin synthase, sepiapterin reductase, or the two regenerating enzymes, pterin-4-carbinolamine dehydratase, and dihydropteridine reductase. Defects in BH4 metabolism can result in hyperphenylalaninemia and deficiency of the neurotransmitters dopamine and serotonin. Changes in CSF neopterin may also occur in deficiency of the BH4 synthesis pathway. Disorders of BH4 metabolism are characterized by a wide range of symptoms that may include developmental delay, mental disability, behavioral disturbances, dystonia, Parkinsonian symptoms, gait disturbances, speech delay, psychomotor retardation and ptosis. In guanosine triphosphate (GTP) cyclohydrolase I (GTPCH) deficiency, neopterin and biopterin levels are low. In 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency, the neopterin level is high and the biopterin level is low. In dihydropteridine reductase (DHPR) deficiency, the neopterin level is in the reference range or slightly increased, and the biopterin level is high. In carbinolamine-4a-dehydratase (PCD) deficiency, the neopterin level is initially high, the biopterin level is in the subnormal range, and a primapterin level (7-substituted biopterin) is present. Neopterin is released from macrophages and astrocytes following stimulation by interferon gamma. It is a non-specific marker for immune system stimulation. An elevation in cerebrospinal fluid can be useful to help differenciate between immune problems and other causes of neurological disease.