  It is shown that the potential for lepton-antilepton bound states (leptonium)
is the Fourier transform of the first Born approximation to the QED scattering
amplitude in an 8-component equation, while 16-component equations are
excluded. The Fourier transform is exact at all cms energies $-\infty < E <
\infty$; the resulting atomic spectrum is explicitly CPT-invariant.
