GRM5 and fragile X syndrome: In vitro binding assays employing [3H]-labeled 3-methoxy-5-pyridin-2-ylethynylpyridine (MPEPy) in prefrontal cortex tissue homogenates from subjects with fragile X syndrome (FXS) vs. controls found a marginally significant increase in mGluR5 density (p < 0.058) in subjects with FXS [14].