Role of Adenosine Receptors in Rare Neurodegenerative Diseases with Motor Symptoms.

The approval of istradefylline, an adenosine 2A receptor (A2AR) antagonist, as an addon treatment in adult patients with Parkinson's disease by the Food and Drug Administration (FDA) and European Medicines Agency (EMA), is the latest proof of the importance of the adenosinergic system in the nervous system. Adenosine is an endogenous purine nucleoside with a role as a modulator of both neurotransmission and the inflammatory response. As such, the expression pattern of the 4 adenosine receptors (A1R, A2AR, A2BR and A3R) and the extracellular adenosine levels have attracted great interest in the pathogenesis and possible treatment of rare neurodegenerative diseases with motor symptoms. These include Huntington's Disease (HD), Amyotrophic Lateral Sclerosis (ALS), Multiple Sclerosis (MS), Restless Legs Syndrome (RLS) and Machado-Joseph Disease (MJD, also known as spinocerebellar ataxia type 3, SCA3). In this review, we shall focus on the role of the different adenosine receptor subtypes in the development and possible treatment of the aforementioned rare neurodegenerative diseases with motor symptoms using the currently available data. The last section discusses the possibility of a role for the adenosine receptors in the treatment of other rare diseases based on the available molecular pathology knowledge.