Diagnosing Alzheimer’s

Study explores potential for assaying biomarkers in tears

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Tear biomarkers could prove useful as a diagnostic tool for Alzheimer’s disease, suggests a pilot trial conducted at Maastricht University. The research was presented by Marlies Gijs PhD, at the annual meeting of the Association for Research in Vision and Ophthalmology (ARVO) in Vancouver, Canada. “Tears are known to contain thousands of molecules and specific biomarkers in tears have been identified for ocular, systemic, and neurologic diseases, but so far no one has looked for tear-specific biomarkers for Alzheimer’s disease,” said Dr Gijs, a postdoctoral researcher in the School for Mental Health and Neuroscience, Maastricht University Medical Centre, the Netherlands. “Although Alzheimer’s disease is commonly viewed as a disorder of the brain, more and more it is being regarded as a systemic disease with dysfunctions in peripheral tissue and also the eye.” Dr Gijs said that retinal nerve fibre layer thinning and changes in retinal vasculature are the best known ocular components of dementia. In addition, amyloid plaques have been detected in the eye and the amyloid precursor protein has been shown to be expressed by the acinar cells of the lacrimal gland and secreted into tears. To look for tear biomarkers of Alzheimer’s disease, the study analysed levels of total-tau and amyloid-β 42 (Aβ42) in samples collected using Schirmer strips. The study included 34 subjects who represented four subgroups: persons with Alzheimer’s disease, persons with mild cognitive impairment, persons with subjective cognitive impairment, and age-matched healthy controls. Dr Gijs reported that the concentration of total-tau increased with increasing dementia severity and that the concentration of Aβ42 decreased as dementia severity increased. A receiver operating characteristic curve analysis was also done to explore the performance of the two parameters for discriminating between healthy and diseases states, and the results were compared with those achieved using total-tau and Aβ42 levels in cerebrospinal fluid (CSF). The results showed that tear total-tau and Aβ42 each had reasonable discriminatory power – area under the ROC curve values were 0.81 and 0.725, respectively, and higher than those found using the CSF. “We are now planning a larger study with 305 patients to validate our pilot results that suggest a relationship between tear biomarkers and the severity of dementia,” said Dr Gijs. “Our study also shows that tear biomarkers provide valuable information for non-ophthalmic conditions. That is why at the University Eye Clinic at Maastricht, we collect all Schirmer tear strips.” Marlies Gijs: marlies.gijs@mumc.nl