However, the occurrence of tremor in patients with normal testosterone levels, along with the inconsistent therapeutic benefit of testosterone replacement, argues against a purely androgen-deficiency – based explanation.Several genes located on the X chromosome have been implicated in tremor disorders – including FMR1 in FXTAS, the androgen receptor gene in Kennedy’s disease, and PLP1 in the Xq22–27 region associated with Pelizaeus–Merzbacher disease – raising the possibility that X-linked genetic influences contribute to the phenotype. This evidence concerns the gene FMR1 and fragile X-associated tremor/ataxia syndrome.