  We present an analysis of isospin-breaking effects in threshold pion-nucleon
scattering due to the light quark mass difference and the dominant virtual
photon effects. We discuss the deviation from various relations, which are
exact in the isospin limit. The size of the isospin-violating effects in the
relations involving the isovector $\pi N$ amplitudes is typically of the order
of one percent. We also find a new remarkably large effect $(\sim 40%)$ in an
isoscalar triangle relation connecting the charged and neutral pion scattering
off protons.
