On the other hand, mGluR1 loss of function has been unveiled in a large number of animal models of human cerebellar ataxia such as SCA1 transgenic mice carrying an expanded number of CAG repeats in the ataxin gene, which results in a poly-glutamine tract (polyQ) expansion in the ataxin-1 protein (Serra et al., 2004; Orr, 2012). Here, GRM1 is linked to cerebellar ataxia.