GDNF and Tinnitus: PCR-based RFLP analysis in 240 German patients with Tinnitus Questionnaire (TQ)-scored subjective chronic primary tinnitus (Goebel and Hiller, 1994) has been performed for the genes BDNF and GDNF, encoding brain and glial cell-derived neurotrophic factors, respectively (Sand et al., 2012b).