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No evidence for new variant of autism caused by MMR

 

Bottom line

No evidence was found to support the existence of a distinct syndrome of MMR-induced autism, or of autism linked with gastrointestinal problems.

Reference:

E Frombonne, S Chakrabati. No evidence for a new variant of Measles-Mumps-Rubella-induced autism. Pediatrics 2001 108:e58 ( http://www.pediatrics.org/cgi/content/full/108/4/e58 )

 

It has been suggested by parents and others that there is a new type of autism caused specifically by the MMR vaccine. The purportive new variant is a combination of developmental regression and gastrointestinal symptoms occurring shortly after immunisation. There are three separate claims:

  1. That there is a new phenotype of autism involving regression and gastrointestional symptoms.
  2. That this new variant is responsible for increases in autism rates.
  3. That this new phenotype is associated with biological findings suggestive of persistent measles infection.

Study

The first of these claims has been tested using information on three sets of children. The main sample was 97 children with pervasive developmental disorders from Staffordshire born between 1992 and 1995. Autistic disorder was present in 26 children, atypical autism in 56, Asperger syndrome in 13 and childhood disintegrative disorder in 1 (one child with Rett syndrome was excluded). All had been vaccinated with MMR.

Two clinical samples for comparison were from the Maudsley Hospital. The MHC sample was 68 children born between 1987 and 1996 who had a confirmed diagnosis of pervasive developmental disorders, and exposed to MMR.

The MFS sample included 99 patients with a diagnosis of autism and born between 1954 and 1979, and therefore not exposed to MMR.

For all three samples detailed information was available on the children, and from medical notes and parents.

Results

Age at first parental concern has not changed

There was no difference in the mean age of first parental concern in the three study samples, and was about 19 months in each sample (Table 1).

Table 1: characteristics of the three samples

 

MFS sample

MHC sample

Stafford sample

Number of children

98

68

96
Birth period

1954-1979

1987-1996

1992-1995
MMR status

Pre-MMR

Post-MMR

Post MMR
Age at first parental concern (mean, months)

19.5

19.2

19.2
Regression probable (%)

14

7
Regression definite (%)

4

8
Any regression (%)

18

16

Rate of regressive autism has not increased

In two samples for which information on regressive autism was available, there was no difference in the proportion with any form of regressive autism (or definite, or probable) in children exposed or not exposed to MMR (Table 1). Parents with children with regression did not become concerned at an earlier age than parents of children without regression.

There was no association between regression and gastrointestinal symptoms

Gastrointestinal symptoms were reported for 19 children, with constipation being the most common, followed by abdominal pain, bloody stools, and diarrhoea. Bloody stools were mostly transient and associated with constipation. No child has inflammatory bowel disorder, or had medical investigations for bowel syndromes. No association was found between gastrointestinal symptoms and regression. Only two children in the whole sample (2%) had both gastrointestinal symptoms and regression, lower than what could be expected by chance.

Comment

This is a lovely study from the Institute of Psychiatry. It set out to test whether there was a new variant of autism caused by MMR and associated with regression and gastrointestinal symptoms. Using three well worked up samples of children both exposed and not exposed to MMR, it could find absolutely no evidence for any effect. Indeed, one might even turn this round and say that if there was no evidence from this sample, there was no evidence at all.

The authors go on to point out that regression in autism is not a new phenomenon. In a review of the literature they demonstrate regression rates of 22% to 50% in studies between 1963 and 1998 (Table 2). The variation between studies is what might be expected by chance given the small numbers of some of the studies, but it is clear that regression occurred in children with autism long before MMR. In this study regression occurred in 18% of autistic children in a pre-MMR sample and in 16% of autistic children in a post-MMR sample.

Table 2: Review of studies examining regression in autism

Year of publication

Number of children

Regression definition

Regression rate (%)

1963

100

 Setback in development

25
1964

14

 Setback in development

50
1966

32

 Setback in development including speech loss

31
1974

116

 Retrogressive shift with speech disappearance

22
1985

261

 Speech/gesture loss lasting over six months

37
1998 (children born before 1975)

179

 Normal development followed by loss of words for minimum of three months

30

Whatever way you look at it, there is no evidence here for any increase in regression, nor any association between gastrointestinal symptoms and regression, nor any change in the descriptions of autism before or after MMR was introduced. Yet another brick in the wall indicating lack of any association between MMR and autism.