MMR vaccination, ileal lymphoid nodular hyperplasia, and pervasive developmental disorder

Andrew Wakefield and colleagues have raised the possibility that a subset of children with PDD, particularly those with a history of developmental regression and chronic gastrointestinal symptoms, have a dysregulated immune response to measles antigen associated with intestinal abnormalities.2,3,8 In 1998 Wakefield's group reported on a group of children with PDD and other psychiatric and neurological disorders referred to a gastroenterology clinic for evaluation of a range of chronic gastrointestinal symptoms, including abdominal pain, bloating, and diarrhoea.3 12 children were evaluated, and, strikingly, 11 had deal lymphoid hyperplasia without granulomas.3 A subsequent study by this group noted ileal lymphoid nodular hyperplasia in 93% of affected children compared with 14% of control children.2 A possible link between deal lymphoid nodular hyperplasia and MMR vaccination was suggested in these reports based on a temporal association between the administration of vaccine and the onset of symptoms in many cases.2,3 A potentially important sample bias in these investigations is that patients were identified because of referral to a gastroenterology clinic. Of interest would be evaluation of PDD patients with and without gastrointestinal symptoms to determine if features such as a history of developmental regression are more common among those patients with PDD found to have ileal lymphoid nodular hyperplasia.