USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

Which symptoms are associated with Dopamine beta-hydroxylase deficiency in infants?

1. Exercise intolerance

2. Impaired sympathetic adrenergic activity

3. Sweating abnormalities

4. Hypotension, ptosis, hypothermia

The correct answer is: Hypotension, ptosis, hypothermia

Dopamine beta-hydroxylase (DBH) deficiency is a rare genetic disorder that results in the inability to convert dopamine into norepinephrine. This enzymatic block affects the functioning of the sympathetic nervous system, which is responsible for various physiological responses, including those associated with the fight-or-flight reaction. In infants with DBH deficiency, the most notable symptoms arise from the lack of norepinephrine and the resulting impaired sympathetic adrenergic activity. This deficiency leads to symptoms like hypotension (low blood pressure), as norepinephrine is crucial for maintaining vascular tone and blood pressure. The other symptoms, such as ptosis (drooping eyelids) and hypothermia (inability to maintain normal body temperature), reflect the overall impact of insufficient catecholamines on systemic physiological functions. The infant's inability to effectively mobilize cardiovascular and thermoregulatory responses leads to these observable signs. While other symptoms such as sweating abnormalities or exercise intolerance might manifest in more complex forms of sympathetic dysfunction, the triad of hypotension, ptosis, and hypothermia is particularly characteristic of this condition as a direct consequence of neurotransmitter depletion.