Complex sentence: The existence of autistic enterocolitis is unproven, as Wakefield's fraudulent studies used inadequate controls, he suppressed negative findings in his now retracted reports, and multiple attempts to replicate his results have been unsuccessful.
Split into simpler sentences: The existence of such an enterocolitis has been dismissed by experts as having "not been established", and Wakefield's fraudulent studies used inadequate controls and suppressed negative findings in the now-retracted reports. Multiple attempts to replicate his results have been unsuccessful.