Abstract. Amyotrophic lateral sclerosis (ALS) is a fatal, neurodegenerative disorder caused by degeneration of motor neurons.The cause for most cases of ALS is multi-factorial,this enhances the need to characterize and isolate specific biomarkers found in biological samples from ALS patients. To this end we use human mesenchymal stem cells (hMSC) derived from the bone marrow of six ALS patients (ALS hMSC) and identified two genes, Cytoplasmic FMR Interacting Protein 2 (CyFIP2) and Retinoblastoma (Rb) Binding Protein 9 (RbBP9) with a significant decrease in post transcriptional A to I RNA editing compared to hMSC of healthy individuals. At the transcriptional level we show abnormal expression of these two genes in ALS hMSC by quantitative real time-PCR (qRT-PCR) and Western blot suggesting a problem in the regulation of these genes in ALS. To strengthen this view we tested by qRT-PCR the expression of these genes in peripheral blood leukocytes (PBL) isolated from blood samples of 17 ALS patients and found that CyFIP2 and RbBP9 levels of expression were significantly different compared to the levels of expression of these two genes in 19 normal PBL samples. Altogether we found two novel ALS potential biomarkers in non-neural tissues from ALS patients that may have direct diagnostic and therapeutic implications to the disease.Keywords: ALS biomarkers, CyFIP2, RbBP9, human mesenchymal stem cells, leukocytes BackgroundALS is a fatal and incurable neurodegenerative disorder characterized by progressive loss of motor neurons in the spinal cord, brainstem and motor cortex, resulting in generalized weakness and muscle atrophy. ALS is the most common motor neuron disorder, with a prevalence of 6 per 100,000 at any given time [1]. Approximately 90% of the cases are sporadic, and the remaining 10% are familial [2]. Over 100 distinct mu- [6]. Moreover, previous study in our laboratory reveals that these stem cells bearthe rare biological capacity to survive for prolonged time under serum free culture conditions due to the production of their own survival factors, like bone morphogenetic protein [7].RNA editing is a post-transcriptional mechanism for expanding the proteomic repertoire. Adenosineto-inosine (A to I) RNA editing by enzymes named ADARs (adenosine deaminases acting on RNAs) is essential for normal life and development of both invertebrates and vertebrates [8][9][10]. When functioning improperly, this essential process, can lead to pathological conditions ranging from epilepsy to malignant gliomas [11][12][13]. So far, only abnormal RNA editing at the Q/R (glutamine/arginine) site of the GluR-2 gene of the AMPA (Amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptor has been identified to be implicated in ALS [14][15][16][17]. It is unknown whether the RNA editing deficiency in the GluR-2 gene is part of a more global RNA problem related with ADARs activity in ALS [18].Here we show that ALS hMSC have abnormal pattern of RNA editing in two novel genes, CyFIP2 and RbBP9, which also expressed significantly differen...