One of the biggest changes is an increase in the use of attenuated strains or non infective versions of many diseases, introduced in the form of vaccines. At the same time, levels of mercury injected into infants in the form of preservatives (thimerosal) increases every time another infection is added to the list of recommended or mandatory vaccine programmes.
The other big change involves the fact that the older organochlorine (OC) insecticides have been replaced by those based upon organophosphorus (OP) compounds.
This leads us to a consideration of infectious agents and environmental chemicals, and their effects on the immune system, in what we have termed the 'opioid excess theory of autism' (see box below).
Dr Andrew Wakefield, of the Royal Free Hospital in London, which specialises in bowel disease, published a study of 12 autistic children showing that all 12 had gross intestinal abnormalities, with 11 showing ileolymphoid nodular hyperplasia, patchy chronic inflammation of the colon and abnormal growth of small nodules of lymphoid tissue (Lancet, 1998; 351: 637-41). Two children had thrush like ulcers plus huge swellings in the small bowel. In all cases, the children had been developing normally when they suddenly lost their speech and other skills, and began exhibiting symptoms of autism. Eight of the 12 developed autistic symptoms within 14 days of receiving the MMR jab.
All the other heavily quoted contributions to this debate (Lancet, 1999; 353: 2026-9; Lancet, 1998; 351: 1327-8; Autism, 1998; 2: 423-4) have relied on the manipulation of epidemiological data or, as in the case of Fombonne (Lancet, 1998; 351: 955) and Afzal (Lancet, 1998; 351: 646-7), are not relevant to the situation.
In a review of our own records, we attempted to demonstrate that those children who according to their parents showed dramatic and rapid behavioural regression within a very short time of receiving the combined MMR vaccine formed a separate subgroup within the autistic spectrum. We were able to outline certain clinical characteristics which we believe could be useful in defining this group.
In addition, our evidence suggested that certain children, diagnosed with some form of autism, have urinary peptide profiles at least in the majority of these children that differ significantly from those obtained from people who have more typical forms of autism. Wakefield's work suggests there are identifiable biological differences (see box, p 2).
When urine samples are taken from children diagnosed with autism and related disorders, a majority up to 80 per cent show increased levels of indolyl acryloyl glycine (IAG) in the urine, an abnormal metabolite of the amino acid tryptophan that may be created under certain conditions during tryptophan metabolism (Amino Acids, 1999; 17: 401-3).
As yet, there's no published evidence that IAG has any marked physiological activity (though this possibility is being investigated in our laboratory). But, given its molecular size and structure, it is likely that the only known precursor for IAG indolyl acrylic acid (IAcrA) possesses considerable potential for activity. In particular, it could become involved in the structure of cell membrane fats, greatly increasing their permeability to other molecules.
As far as autism is concerned, what particularly interests us is the effect of IAcrA on the permeability of the intestinal wall and the blood brain barrier. Increased permeability would permit the increased translocation of biologically active peptides from the intestines to the central nervous system.