Oral Glucose Tolerance Test Better at Diagnosing Friedreich Ataxia-Associated Diabetes, Study Suggests

The oral glucose tolerance test showed higher sensitivity, compared with other diagnostic tools, and was able to detect up to three times more metabolic abnormalities in Friedreich ataxia patients, who commonly experience diabetes and impaired sugar tolerance, according to a small study.

“Clinicians in charge of Friedreich ataxia patients and researchers should incorporate the OGTT (oral glucose tolerance test) as an accurate diagnostic and research tool,” the study’s researchers wrote.

Their study, “OGTT is recommended for glucose homeostasis assessments in Friedreich ataxia,” was published in the journal Annals of Clinical and Translational Neurology.

Friedreich ataxia (FRDA) is an inherited, neurodegenerative disease caused by a mutation on the FXN gene, leading to a defective production of the frataxin protein. Frataxin is key for the proper functioning of nerve and muscle cells. To get FRDA, a child must inherit two copies of the defective (mutated) gene, one from each parent.

In FRDA, nerves that carry signals from the muscles to the brain degenerate, which causes progressive walking disturbances, uncontrolled muscle tone or spasticity, loss of sensory perception, and absent reflexes.

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Other FRDA complications include impaired glucose (sugar) tolerance and diabetes mellitus, with diabetes prevalence varying between 8% to 32% in these patients.

Diabetes is diagnosed when fasting glucose blood levels are equal or above 126 milligrams per deciliter (mg/dL), whereas normal glucose levels should be below 100 mg/dL in measurements done on two separate days.

The OGTT is another way of diagnosing, and measures the sugar levels two hours after ingesting 75 grams of glucose. Levels above 200 mg/dL mean diabetes, and below 140 mg/dL is considered normal.

In this study, researchers compared the efficacy of the OGTT to other glucose tests as a way to diagnose diabetes in FRDA patients. They analyzed a group of 41 FRDA patients with 26 first-degree relatives that carried one copy of the FXN mutation, and 53 healthy volunteers. The three groups underwent OGTT and intravenous glucose tolerance tests.

The OGTT identified more cases of impaired glucose tolerance or diabetes compared with the fasting glycemia test.

Eight FRDA patients were confirmed as positive for impaired glucose tolerance and two for diabetes using the OGTT test but not the fasting glycemia test. This meant that 40% of cases went undetected when using the fasting glycemia test.

Also, the OGTT was able to measure the level of function of the pancreatic cells responsible for insulin production — the hormone that regulates blood sugar — and insulin secretion.

“Our data show that the OGTT provides accurate measures of key variables controlling glycemia, as well as a sensitive assessment of glucose tolerance,” the researchers wrote.

“The OGTT can be done in clinical routine and in clinical research settings, without the need for specialized personnel,” they added.