Normal melanocytes do not express mGluR1, the ectopic expression of a normal neuronal receptor, mGluR1 in melanocytes leads to cellular transformation in vitro and spontaneous metastatic melanoma formation in vivo with 100% penetrance (Figure 2 and Figure 3) [64,66,67,74,76,77,78,79,80,81,82]. The gene discussed is GRM1; the disease is metastatic melanoma.