GRM7 and presbycusis: Grm7, glutamate receptor 7, with a role in neuroprotection, synaptic transmission, and regulation of Ca++ ion transport via voltage gated Ca++ channel activity, has been shown to confer susceptibility to many neuropathologic conditions such as age-related hearing impairment [57, 60, 61], attention-deficit/hyperactivity disorder [58, 62], and schizophrenia [63–65].