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Autoimmune Antibody Identified as Biomarker for Tachycardia Syndrome

By Labmedica International staff writers
Posted on 16 Sep 2019
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Image: G-protein-coupled receptor mechanism (Photo courtesy of Wikimedia Commons).
Image: G-protein-coupled receptor mechanism (Photo courtesy of Wikimedia Commons).
Results published in a recent paper suggested that postural orthostatic tachycardia syndrome (POTS) was probably an autoimmune disorder and may boost the development of a simple blood test to diagnose the condition.

Postural orthostatic tachycardia syndrome (POTS) is a condition in which a change in position from lying to standing causes an abnormally large increase in heart rate. This occurs with symptoms that may include lightheadedness, trouble thinking, blurred vision, or weakness. Other commonly associated conditions include irritable bowel syndrome, insomnia, chronic headaches, Ehlers–Danlos syndrome, chronic fatigue syndrome, and fibromyalgia.

The causes of POTS are varied. Often, it begins after a viral infection, surgery or pregnancy. Risk factors include a family history of the condition. Diagnosis in adults is based on an increase in heart rate of more than 30 beats per minute within ten minutes of standing up which is accompanied by symptoms.

Investigators at the University of Toledo (OH, USA) collected detailed clinical symptoms from 55 patients (including 52 females with an average age of 30 years) diagnosed with POTS. They also evaluated serum levels of autoantibodies against four subtypes of G‐protein coupled adrenergic receptors and five subtypes of G‐protein coupled muscarinic acetylcholine receptors by ELISA.

Results revealed a significant number of patients with elevated levels of autoantibodies against the adrenergic alpha 1 receptor (89%) and against the muscarinic acetylcholine M4 receptor (53%). Four patients had elevations of G‐protein coupled autoantibodies against all nine receptor subtypes measured in the study. Five POTS patients had no elevation of any autoantibody; similarly, controls were also negative for autoantibody elevations.

The results indicated that autoantibodies against adrenergic A1 subtype receptor would be present in about 90% of patients with POTS, which suggested that this receptor could serve as a biomarker for diagnosis of the disorder.

"The trouble with diagnosing POTS is that it is currently principally a clinical diagnosis. It is based on history, the absence of other illness as well as the finding of increase in heart rate when standing. There is no blood test right now to aid in the diagnosis. It can be an incredibly frustrating process for patients," said senior author Dr. Blair Grubb, professor of medicine and pediatrics at the University of Toledo. "People have suspected an autoimmune connection for years, and other small-scale studies have suggested it. We did a much larger cross-section of patients than has ever been done before, and found that almost all of them tested positive for autoimmune antibodies. That is a significant finding."

The POTS autoimmune antibody study was published in the September 9, 2019, online edition of the Journal of the American Heart Association.

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