Asperger's is a syndrome - that is, a condition defined and diagnosed only by reference to its symptoms. Doubting that there is a single underlying cause is valid, and not even terribly controversial - one of the two psychs who diagnosed me (earlier this year; I'm in my mid-30s) told me that she could buy that as a label it could apply to half a dozen or more underlying causes. But doubting that it's a syndrome is... well, a bit silly. :)
Not quite, a syndrome is a set of correlated symptoms.
Basically, consider the sumptoms of deafness, impotence and tingling in the hands and feet (D, I and T). Suppose that deafness, impotence and tingling are all independent of each other (P(D | I) = P(D)). In this case, there is no syndrome. If, however, they are strongly correlated(P(D | I) >> P(D)), we have a syndrome.
Basically, "deaf and impotent provides no information about tingling" == no syndrome.
"Deaf and impotent implies a high probability of tingling" == syndrome.
