  Synchrotron diffraction as a function of temperature and pressure, specific
heat, magnetic susceptibility and small-angle neutron scattering experiments
have revealed an anomalous response of MnGe. Similar but less pronounced
behavior has also been observed in Mn$_{1-x}$Co$_x$Ge and Mn$_{1-x}$Fe$_x$Ge
solid solutions. Spin density fluctuations and Mn spin state instability are
discussed as possible candidates for the observed effects.
