The answer is a definite yes that lab topaz exists. I found two scientific papers on its synthesis. The paper dated 1993, made mention to earlier synthesis in 1973 by Rosenberg. I have not been able to locate Rosenberg's paper, so the first synthesis may be earlier than that. The 1993 paper was authored by B. Wunder, et al in American Mineralogist, 78, 285-297; "Synthesis, stability, and properties of Al2SiO4(OH)2: a fully hydrated analogue of topaz". I never see any natural looking inclusions in the "mystic topaz" (optically coated clear or white topaz) coming out of Thailand or China nor in much of the neutron bombarded blue color enhanced topaz as well ... so at this point, I would have to conclude from general observation that most of it is being synthesized cheaply somewhere somehow!!