Moreover, through genetic crosses we directly show for the first time that reducing GLAST levels has a severe consequence on the severity of ataxia in β-III-/- animals with young β-III-/-/GLAST+/- mice displaying a much earlier decline in motor performance than either β-III-/- or GLAST-/- animals highlighting a synergistic effect of reduced GLAST and loss-of β-III spectrin function, likely due to a combined loss of EAAT4 and GLAST, the two predominant glutamate transporters in the cerebellum. Here, SLC1A6 is linked to cerebellar ataxia.