Isosinglet fermions naturally arise in a variety of extensions of the Standard Model, in particular in models with extra-dimensions. In this paper, we study the effect of the addition of a new isosinglet charged lepton to the standard spectrum, with special emphasis on implications for neutrino asymmetries to be measured at future neutrino factories. Lepton flavour violation in neutral current and lepton universality constraints are extensively discussed. We show that New Physics effects in ν e -ν μ CP asymmetries are significantly enhanced due to leptonic maximal mixings but still too small to give a signature at future neutrino factories. A signal for CP asymmetries in ν μ -ν τ channel due to New Physics could be observed at 1-3 σ if lepton-flavour-violating τ decays are seen in a very close future in B-factories like Belle experiment.