Research suggests tear fluid testing as promising method for Huntington’s Disease monitoring

(image credit: AdobeStock/Giovanni Cancemi)

The mutant huntingtin (mHTT) protein in the tear fluid may have the potential to serve as an early and non-invasive marker of changes in Huntington’s disease, based on the results of a European study. First author Marlies Gijs, PhD, from the University Eye Clinic Maastricht, Universiteit Maastricht, Maastricht, Limburg, the Netherlands, reported her group’s findings at the Association of Vision in Research and Ophthalmology in Seattle.

Huntington's disease (HD), an autosomal-dominant, fully-penetrant, neurodegenerative disease that most commonly affects adults during middle age, results from CAG repeat expansion in the HTT gene, resulting in the expression of mutant huntingtin (mHTT) protein, Gijs explained.

In this first-of-a-kind study, she and her colleagues set out to detect and quantify mHTT in the tear fluid. They recruited 20 manifest and 13 premanifest HD gene expansion carriers (HDGECs) and 20 age-matched controls. All patients were assessed using the Unified Huntington’s Disease Rating Scale (UHDRS) total motor score (TMS) and total function capacity score.

The tear fluid samples were collected using Schirmer’s strips. Proteins were extracted by elution and centrifugation and the tear mHTT was determined using the Single Molecule Counting SMCxPRO technology.

Tear fluid results

The level of protein in the tear fluid far exceeded that of normal controls. “The average tear mHTT levels in manifest (67,223 ± 80,360 fM) and premanifest patients (55,561 ± 45,931 fM) were significantly (p < 0.001) higher than in healthy controls (1,622 ± 2179 fM). We noted significant correlations between tear mHTT levels and CAG repeat length, estimated years to diagnosis, disease burden score, and UHDRS TMS,” the investigators reported.

The receiver operating characteristic curve demonstrated an almost perfect score (area under the curve [AUC] = 0.9975) when comparing controls to manifest patients, which indicated a test providing the correct answer 99.75% of the time. In like manner, the AUC between controls and premanifest patients was 0.9846. The optimal cut-off value (= highest Youden index) to distinguish between controls and manifest patients was 4,544 fM, whereas it was 6,596 fM for the distinction between controls and premanifest patients, the author reported.

“The detection of high levels of mHTT in tear fluid from HDGECs in our study endorses that tear fluid is a valuable source for HD biomarkers. Ultimately, tear biomarkers could help the HD community to non-invasively measure the effectiveness of disease-modifying drugs and determine the optimal time and dose to start such therapies,” Gijs and colleagues concluded.

Reference:

Gijs M, Joma N, Datson N, et al. Detection of high levels of mutant huntingtin protein in tear fluid of patients with Huntington’s Disease. Paper presented at: Association for Research in Vision and Ophthalmology annual meeting; May 5-9, 2024; Seattle, WA. Presentation number: 3322