Friedreich’s ataxia patients produce less sweat than healthy people, which may be a useful biomarker of disease severity and progression, a recent study suggests.
The study, “Sudomotor dysfunction is frequent and correlates with disability in Friedreich ataxia,” was published in the journal Clinical Neurophysiology.
Patients with Friedreich’s ataxia have progressive nerve and muscle damage, causing movement discoordination (ataxia) and muscle weakness. This affects not only the limbs, but the eyes, hearing, and speech.
Several neurodegenerative diseases, including some ataxia-related disorders, show dysfunction of the autonomic nervous system, which controls involuntary functions of the body, such as the heart rate, digestion, sexual arousal, and body temperature/sweating.
However, few studies have focused on the autonomic function of Friedreich’s ataxia patients, and it remains unclear if and to what extent it may be affected in these patients.
To this end, researchers in Brazil evaluated the frequency and intensity of autonomic-related symptoms in Friedreich’s ataxia patients, as well as their potential association with disease duration and severity.
The study included 28 adults — 17 women and 11 men — with genetic confirmation of Friedreich’s ataxia and 24 age- and gender-matched healthy adults — 13 men and 11 women. The patients’ mean age was 31.5 years, with a mean disease duration of 13.5 years. Healthy participants had a mean age of 35.8 years.
The researchers conducted a clinical and neurological evaluation of all participants. Disease severity was assessed through the Friedreich’s ataxia rating scale (FARS), and autonomic symptoms were quantified using the Scales for Outcomes in Parkinson’s Disease — Autonomic Questionnaire (SCOPA — AUT), in which higher scores correspond with a higher frequency of autonomic symptoms.
They also assessed heart-related measures, such as blood pressure and heart rate, and defined autonomic dysfunction of the heart according to validated criteria. Sudomotor function, or sweating, was assessed through the Quantitative Sudomotor Axonal Reflex Test (QSART), a validated technique that measures the amount of sweat a person produces upon stimulation.
Friedreich’s ataxia patients had significantly higher SCOPA-AUT scores than healthy people, suggesting that these patients do have autonomic dysfunction. Gastrointestinal, genital/urinary, and sweating domains showed higher scores.
Patients showed no significant differences in cardiovascular SCOPA-AUT scores and heart-related measures from healthy individuals, except for the presence of tachycardia (faster heartbeat) at rest — which has been reported in previous studies.
People with Friedreich’s ataxia had significantly smaller volumes of sweat than healthy participants, and lower sweat production was significantly associated with higher disease severity (higher FARS scores).
The researchers noted that these results are consistent with previous reports showing a significant loss of nerve fibers in the skin and a reduced number of nerves in sweat glands.
These findings suggest that sweating problems could be used as a biomarker of Friedreich’s ataxia, and that QSART, which is a fast and non-invasive technique, could be used to monitor disease progression or treatment response in clinical trials. Nevertheless, additional studies are needed to confirm this utility, the team noted.
According to the researchers, the study exposed the presence of several autonomic symptoms in Friedreich’s ataxia patients, some of which could possibly be eased with treatment.
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