Screening for acute hepatic porphyria in postural tachycardia syndrome

Postural orthostatic tachycardia syndrome (POTS) is characterized by an excessive heart rate increase upon standing, often associated with dizziness, gastrointestinal symptoms, and decreased functional capacity. Acute hepatic porphyrias (AHP) are rare metabolic disorders with nonspecific neurovisceral and autonomic symptoms, some of which overlap with POTS. The purpose of this study was to evaluate AHP by molecular and biochemical testing in patients with POTS.

We studied 50 patients diagnosed with POTS and gastrointestinal symptoms at the Vanderbilt Autonomic Dysfunction Center. They underwent neuro-hormonal evaluation for POTS and genetic and biochemical screening for AHP. Genetic testing was aimed mainly at the four genes relevant to AHPs. Porphobilinogen (PBG), delta-aminolevulinic acid (ALA), and total porphyrins were measured in urine with normalization to creatinine.

The average age of the patients was 33 ± 8.6 years, 96% were female, and the average BMI was 28 ± 7.2 kg/m², average systolic blood pressure was 120 ± 15.5 mmHg, average heart rate was 77 ± 13.6 bpm at baseline, and average SBP was 126 ± 19.1 mmHg. A heart rate of 111 ± 15.8 bpm at 10 min upright, showed normal cardiovascular reflexes. The COMPASS-31 total score was 32 ± 8.4, with a normal autonomic function test. Urine PBG averaged 1 ± 0.7 mg/g creatinine, ALA 2 ± 0.9 mg/g creatinine, and total porphyrins 172 ± 74.2 mmol/g creatinine, which were all normal. None had variants in the four genes associated with AHPs. Three patients were heterozygous for a common low expression ferrochelatase gene variant (FECH).

We found no evidence of AHP in patients with POTS with uncontrolled gastrointestinal symptoms, suggesting that screening for AHP, a rare genetic disorder, may not be warranted.