A gene expression signature for Alzheimer’s from finger prick blood spotted on a filter paper card

Abstract

AbstractBackgroundThere is an unmet need for a minimally invasive clinical test using samples collected by medical staff or by self‐collection to screen persons at risk for Alzheimer’s disease (AD) for initial diagnosis as well as for monitoring progression. Addressing this need is even more challenging for underserved and rural populations. Currently, use of whole blood has required venipuncture and RNA extraction. None‐the‐less, AD gene expression signatures using RNA extracted from whole blood have been reported by a number of groups. We have developed a direct, extraction‐free TempO‐Seq® assay of gene expression using blood from a finger prick spotted on filter paper. This novel method is perhaps the simplest and least invasive method of obtaining a blood sample and performing a test that can be used to identify a diagnostic Alzheimer’s signature.MethodThe targeted sequencing of the whole transcriptome via the TempO‐Seq® gene expression assay (Yeakley, PLosOne doi.org/10.1371/journal.pone.0178302) was adapted to utilize blood spotted on filter paper. Samples were obtained under an IRB‐approved protocol from normal volunteers and patients clinically diagnosed with AD or Parkinson’s disease (PD).ResultA protocol that eliminated interference by components of whole blood with enzymes used in molecular biology assays was successfully implemented. This permitted a TempO‐Seq assay to be carried out without extraction of RNA from the filter paper blood spots. Highly expressed genes were attenuated to increase the sensitivity with which AD biomarker genes could be measured. The shelf‐life of blood spotted filter paper stored at room temperature was greater than 6 months. AD, PD, and normal control blood samples were assayed and a proposed gene expression signature for AD was identified.ConclusionUse of a simple gene expression‐based assay of blood from a finger prick spotted on filter paper to diagnose AD is feasible. The spotted blood sample is stable for months at room temperature, permitting self‐collection or assisted collection and mailing of samples for testing.