Dopamine agonists in dihydropteridine reductase deficiency

The traditional treatment of severe disorders of tetrahydrobiopterin (BH4) metabolism is based on the replacement therapy with BH4, 5-hydroxytryptophan, and L-dopa. Major problems are encountered with L-dopa therapy, especially with increasing age when higher doses are necessary, because of its short half-life and adverse effects. Consequently, different L-dopa-sparing strategies have been successively introduced, with partial reduction of L-dopa dosage and amelioration of the clinical outcome. Recently, we demonstrated that the dopamine agonist pramipexole improves the therapeutic effect of L-dopa in 6-pyruvoyl tetrahydropterin synthase (PTPS) deficiency, the most common disorder of BH4 metabolism. Here we report its effectiveness in two patients (males, 7 and 22 years) with dihydropteridine reductase (DHPR) deficiency, the second most frequent cause of BH4 deficiency. Both patients experienced residual symptoms of dopamine deficiency, movement and behavioral disability, and complications of L-dopa therapy, associated with fluctuating hyperprolactinemia. They had full clinical and biochemical assessment, by an adapted Unified Parkinson's Disease Rating Scale (UPDRS) and measurement of diurnal plasma prolactin (PRL) profile before and after a trial with pramipexole. Besides allowing the reduction of L-dopa daily dosage (-58%) and administrations (from three to two) in one patient and to stop L-dopa therapy in the other, the introduction of pramipexole markedly improved and stabilized clinical and biochemical picture in both patients, as revealed by reduction of UPDRS scores and normalization of diurnal plasma prolactin profiles. Dopamine agonists can improve or even replace L-dopa therapy in disorders of synthesis and regeneration of BH4.