Dysfunctional BDNF signaling has been demonstrated in several pathophysiological mechanisms of RTT disease progression (Katz, 2014; Li and Pozzo-Miller, 2014), but the contribution of the BDNF val66met SNP to RTT symptoms remains unclear: one study reported that the met BDNF allele is protective for seizure onset in RTT individuals (Nectoux et al., 2008), while another described that it leads to earlier seizure onset (Zeev et al., 2009). The gene discussed is BDNF; the disease is Rett syndrome.