  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 $\nu_e-\nu_{\mu}$ 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 $\nu_{\mu}-\nu_{\tau}$ channel due to new physics could be
observed at $1-3 \sigma$ if lepton flavour violating $\tau$ decays are seen in
a very close future in B-factories like BELLE experiment.
