Dopamine beta-hydroxylase (DBH) is a key enzyme in the conversion of dopamine to norepinephrine in the central nervous system and is the enzyme needed for the conversion of dopamine to norepinephrine in the sympathetic nervous system of the autonomic nervous system. Dopamine beta-hydroxylase can be readily measured in serum and correlates highly with the amount of the same enzyme in the cerebral spinal fluid. The DBH gene has been mapped to chromosome 9 at the q34 position. Seventy-one polymorphisms of the DBH gene have been identified in just 80 subjects: 68 single nucleotide polymorphisms (SNPs), two insertion/deletions, and one repeat.
Because of the large number of SNPs, there are a very large number of possible combinations of variants for DBH (4,970 combinations).