Monitoring treatment in tetrahydrobiopterin deficiency by serum prolactin

Hyperphenylalaninaemia, dopamine and serotonin deficiencies are the main metabolic disturbances caused by tetrahydrobiopterin (BH 4 ) deficiency, irrespective of the enzyme defect leading to impaired cofactor synthesis or regeneration. While hyperphenylalaninaemia can be easily controlled by dietary or synthetic cofactor treatment, it is often hard to ensure neurotransmitter homeostasis at the central level by administering the hydroxylated precursors. Major concerns are with their optimal dosages, as neither biochemical measurement of CSF neurotransmitter metabolites nor clinical monitoring are adequately informative (Ponzone et al 1990 ; Spada et al 1992). Since dopamine is the essential inhibitory factor of prolactin (PRL) secretion, we evaluated serum PRL levels in seven BH 4 -deficient patients before and while on therapy as a simple tool for treatment monitoring.