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    32 Dopamine β-hydroxylase (DBH)
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    32 Dopamine β-hydroxylase (DBH)

    Dopamine β-hydroxylase: enzyme forming noradrenaline, marker of sympathetic activity and DBH deficiency.

    Dopamine β-hydroxylase (DBH) is the enzyme that converts dopamine into noradrenaline (norepinephrine). It is the only enzyme in the synthesis of small-molecule neurotransmitters that is bound to membranes, inside the storage vesicles of noradrenergic nerve endings and the adrenal medulla. When these nerves are stimulated, DBH is released together with noradrenaline, so its activity in blood is a marker of sympathetic nervous system activity. Blood DBH levels differ greatly between people, largely for genetic reasons, but are relatively stable in the same person.

    EnzymesSympathetic nervous systemCatecholamines
    Reactiondopamine → noradrenaline
    Cofactorscopper, vitamin C (ascorbate)
    Located insympathetic nerves, adrenal medulla
    Interpretationrelative to own baseline
    Tyrosine pathways: phenylalanine is converted to tyrosine; tyrosine gives L-DOPA, dopamine, noradrenaline by dopamine beta-hydroxylase, and adrenaline, and is also used for thyroid hormones and melanin From phenylalanine to catecholamines Phenylalanine Tyrosine L-DOPA Dopamine Noradrenaline Adrenaline thyroid hormones, melanin PAH TH DBH PAH = phenylalanine hydroxylase (deficient in PKU); TH = tyrosine hydroxylase; DBH = dopamine β-hydroxylase.
    Figure 1. Tyrosine is the starting point for dopamine, noradrenaline and adrenaline, as well as thyroid hormones and the pigment melanin.

    Clinical significance

    • DBH deficiency: a very rare inherited disorder (autosomal recessive). Noradrenaline and adrenaline are almost absent and dopamine is raised. It causes severe orthostatic hypotension (fainting on standing), drooping eyelids, nasal congestion and, in men, ejaculation problems. It is treated with droxidopa, a precursor converted to noradrenaline without DBH.
    • Short-term decreases: can occur with fatigue, sleep deprivation, long flights or after intense physical exertion
    • Changes in disease: altered activity has been reported in hypertension, some psychiatric disorders, Parkinson disease, and with medicines acting on the sympathetic system; copper deficiency (for example Menkes disease) reduces DBH function
    When to see a doctor

    Fainting or dizziness on standing up, especially from childhood or adolescence, needs assessment of blood pressure regulation by a specialist.

    References

    This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

    Published on 1 May 2024