There is no known cure for Alzheimer's disease. But early diagnosis can help the patient in lessening the symptoms. In a new study, researchers found Alzheimer’s disease fingerprints in proteins and micro RNAs in the tears collected from Alzheimer's disease patients. The study published in the journal Scientific Reports describe the identification of a protein called elongation initiation factor 4E (eIF4E) as the protein present in the tear fluid of Alzheimer's disease patients in early stage. They also identified another molecular marker, microRNA-200b-5p, in the tears of the patients compared to controls.

The process of cognitive decline is in the works for a number of years before clinical diagnosis of Alzheimer’s disease is possible. The early stage of the disease is detected using costly imaging techniques or testing biomarkers in cerebrospinal fluid. Collecting cerebrospinal fluid is an invasive procedure. There is an aggressive search for biomarkers in less invasive body fluids such as blood or non-invasive fluids such as urine to diagnose the disease at an early stage. A very early stage of Alzheimer's disease is called MCI or mild cognitive impairment. They studied patients in both MCI and Alzheimer's disease categories. There were 9 patients with Alzheimer's disease, 8 with MCI and 15 age-matched controls in the study.

Proteins in tear samples were analyzed by liquid chromatography-mass spectrometry method. Though Alzheimer's disease is characterized by the accumulation of proteins such as amyloid precursor protein and tau in the brain, they were unable to detect these proteins in the tear fluids. The total protein content or tear production was also not different between controls and patient groups. They identified 12 proteins to be present in the majority of Alzheimer's samples, but only present in a small number of control samples. The only protein that was found in both MCI and Alzheimer's, but not in control samples was eukaryotic translation initiation factor 4E (eIF4E).

microRNAs in the tear samples were analyzed by a PCR array that amplified 754 microRNAs from each sample. microRNAs are small RNAs that regulate other RNAs, this is called post-transcriptional regulation. They found MicroRNA-200b-5p to be exclusively detected in Alzheimer's disease samples. They did not find significant difference in the level of this microRNA in MCI compared to controls. According to the authors, “this was not entirely surprising with MCI being a heterogeneous condition both occurring as a result of neurodegeneration during the prodromal stage of most neurodegenerative diseases as well as cognitive impairments due to natural aging”.

The authors speculate that tear fluid collected in a paper strip may eventually be used to quickly test for the presence of these biomarkers.

The study was conducted by a collaborative team of investigators from Ireland and Spain.