They are close together on the spectrum. Very often, by the time someone reaches maturity, or sometime after, they become indistinguishable from someone with Asperger's. The major difference that I have come across in my research seems to be language delay in HFA.
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If a man does not keep pace with his companions, perhaps it is because he hears a different drummer.
Let him step to the music which he hears, however measured, or far away.--Henry David Thoreau