We know that, If we remove one electron from the isotopes of $\mathrm{He}^4$ and $\mathrm{He}^3$, the energy levels, as worked out on the basis of Bohr model will be very close as both the nuclei are very heavy as compared to electron mass. Also after removing one electron from $\mathrm{He}^4$ and $\mathrm{He}^3$ atoms will have one electron as in hydrogen atoms, and the nucleus is much heavier then $\mathrm{H}$ atom. So, stability can remain and these atoms are very close to the H atom so the energy levels are as of Hydrogen and these atom will be very close.