Naturally occurring mutations that predict substitution of a conserved proline in the middle of the fifth transmembrane helix by arginine were found in patients with episodic ataxia type 6 (Jen et al., 2005), EAAT1) and in patients with epileptic encephalopathy (Epi4K Consortium, 2016; Guella et al., 2017), EAAT2). The gene discussed is SLC1A3; the disease is episodic ataxia type 6.