Autism

 What we know
 Incidence
 Environmental risk factors
 Costs

What we know

Autism is a complex neurobiological disorder considered to belong to a spectrum of disorders known as autism spectrum disorders (ASD), which also includes Asperger syndrome, Fragile X Syndrome, Landau-Kleffner Syndrome, Rett syndrome, childhood disintegrative disorder, and PDD-NOS (pervasive developmental disorder not otherwise specified). Autism impairs a person’s ability to communicate and relate to others and is often associated with rigid routines, repetitive behaviours and deficiencies in symbolic thinking. Whilst symptoms can range from quite mild to quite severe, the disease is often accompanied by learning disabilities, and immunologic, gastrointestinal and metabolic abnormalities. Children with ASD can usually be diagnosed by the age of three or four.

The precise causes of autism are unknown. A number of twin studies show that genetic factors play an important role. However, recent research suggests that environmental agents may be involved, and may to a greater or lesser extent influence genetic factors [1].

 There appears to be an increased risk of having an autistic child after exposure to rubella in the first trimester of pregnancy [2].

 According to a Swedish study Thalidomide, a morning-sickness drug, may be a contributing factor [3].

 Exposure to Valproic acid, an anti-seizure medication, early in gestation is also implicated [4].

 Evidence to support the much publicised link between the MMR (measles, mumps, Rubella) vaccine and autism is limited. In 2001, a committee of the Institute of Medicine at the National Academy of Sciences concluded that “the evidence favours rejection of a causal relationship at the population level between MMR vaccine and autism spectrum disorders…” [5]

 Another vaccine-related concern is the use of thiomerosal, an organic mercury compound used as a preservative. Although a committee of the Institute of Medicine (IOM) concluded there was insufficient evidence to establish a link, organic mercury is a potent toxicant of the developing brain [6].

 Methylmercury contamination of fish and dental amalgam, which is known to impact brain development, is another potential risk factor.

 Early exposures to alcohol may, in some cases, be responsible for autism.

 Although there are as yet no conclusive links between autism and chemical exposure, a recent review of scientific literature on the causes of neurodevelopmental disorders implicated a number of industrial chemicals including: lead, methylmercury, polychlorinated biphenyls, arsenic, and toluene [7].

Incidence

Estimates suggest that around 6 in 1000 people in the world suffer from an autistic spectrum disorder. The disease affects more boys than girls. It is generally thought that the prevalence of autism is increasing. This is partially due to changes in diagnostic criteria, terminology, and increased reporting. However, an increase in disease rates cannot entirely be explained by these alone.

Environmental risk factors

Our diets and environment have changed dramatically over the past 60 years, unlike our genes, which have remained relatively unchanged. The increase in prevalence thus raises the possibility of an important contributing role for environmental factors; in addition to supporting arguments for additional research into the disease causes and identification of opportunities for prevention. We know that exposures to various environmental agents during early development, even at low doses, can cause brain injury. To decrease the prevalence of autism may therefore require preventive measures to reduce environmental exposures. In the meantime, a precautionary approach is warranted.

Costs

Estimates of the economic burden of Autism in Europe are lacking. However, a UK study by the Centre for the Economics of Mental Health (CEMH) puts the total annual cost of autistic disorder in the UK at, at least £1 billion [8]. In the US, it is estimated that $9.2 billion is spent on certain neurobehavioural disorders, including intellectual deficits/mental retardation, autism and cerebral palsy [9].

 For more information see the Collaborative on Health and Environment section on Autism