Evidence was lacking to support a “new variant” form of autism, where MMR vaccination is associated with developmental regression and bowel problems. We found no change in the proportion of autistic children with bowel problems or developmental regression over a 20 year period from 1979, a period when MMR vaccination was introduced in the United Kingdom (October 1988). We did find an association between bowel problems and regression in our population, but there was no relation between these factors and MMR vaccination. The occurrence of the two symptoms together might reflect particular dietary problems leading to constipation in some children with autism who have regression, or other unknown influences on factors associated with the development and progress of this pattern of autism. Children with autism who have speech loss have more severe learning difficulties several years later than those without such regression.8
Bowel symptoms have been reported in an epidemiological study of 96 children with autism, born between 1992 and 1995 in Stafford, England.9
All but one of these children had been immunised with MMR vaccine. The study also compared the age at onset of regression and first parental concern with two earlier clinical samples of children, one studied before and the other after the introduction of MMR vaccine (but with no record in those two samples as to whether the individual children had been immunised). No change in the average age of regression or parental concern was noted in the three groups. Bowel problems were recorded only for the most recent sample and, unlike our findings and possibly reflecting smaller numbers, the study found no association between bowel problems and regression. The much larger numbers in our epidemiological study enabled us to look for changes in a population of children with autism over a 20 year period, as well as to allow for possible confounders and, with our complete vaccine linkage, directly to compare regression and bowel symptoms in children who were or were not vaccinated with MMR.
Bowel problems, particularly constipation, occur in many children with various kinds of neurodevelopmental disorder. The percentage we found in our autistic population (17% overall) is closely similar to the 19% previously reported.9
Those authors supplemented and validated information from the clinical records with questionnaire information directly from the families. That percentages in the two studies are similar provides validation of our method of data collection. Although there have been further reports10,11
of a specific bowel disorder associated with autism from the group who originally described the possible syndrome,1
there is little support for the postulated mechanism involving MMR vaccination.12
Many children with autism have unusual diets, often associated with constipation, which might lead to non-specific abnormalities of the bowel. The enteric nervous system is likely to be abnormal in children with autism for whatever the genetic reason for autism turns out to be.12
The frequency of regression in autism is uncertain.13
One study reviewed published evidence and reported rates varying between 22% and 50%.9
Many children with autism have infantile speech, which usually stops in such children, as in developmentally normal children, before age 18 months. In normal children more communicative speech usually overlaps. The failure of this normal communicative speech to develop in children who have autism, coinciding with the disappearance of infantile vocalisations, may be overinterpreted as regression of speech and language. Our figure of 25% with developmental regression, although in accord with other studies,is likely to include many such children and is likely to be an overestimate. Regression was found in only 16% of the contemporary group in the Stafford study, using carefully validated data from a standardised interview for diagnosing autism.9,14
This 16% compared with 18% in the clinical group who were born between 1954 and 1979 (before MMR vaccination).9
These figures support our finding that rates of regression in autism are unchanged over many years.
Our study has the strengths and weaknesses of data based on case notes. Data were not recorded systematically, and there was variability in the level of detail. However, information was available from a variety of sources, including notes from health visitors about the children's early life, and notes from hospitals, child development centres, and other community records such as from schools. Thus a serial record was available for each child, including letters from other centres such as those specialising in autism or paediatric gastroenterology. We assessed the accuracy and consistency of our data collection by duplicating the process independently in 40 cases; interobserver agreement on key variables was over 98%. The review of case notes was carried out independently of the MMR history, which came from a different, independent source (computerised records from the time of vaccination).
A review of each record showed that in 13 children the history given by the parents had changed after the extensive publicity about MMR vaccine and autism. Before the publicity the parents often reported concerns early in their child's life, usually before their first birthday; the current history for the same children recorded symptoms as developing only after MMR vaccination, in some cases shortly after. This bias associated with changes in the history given by the parents necessitates particular care when interpreting the planned self-controlled case series analysis of the present dataset.2,3