The discovery adds further evidence to support the prenatal sex steroid theory of autism first proposed 20 years ago.

 

The sex ratio in autism diagnoses shows that males are three times more likely to develop autism. The male-biased prevalence, together with the finding that autistic girls have a higher mutational load than autistic boys, suggests mechanisms of sexual differentiation in the development of this condition. Several recent findings support this hypothesis.

 

A team of scientists at the University of Cambridge and the State Serum Institute in Denmark tested the amniotic fluid of boys with and without autism (n = 98 and n = 177 respectively) from the Danish Historic Birth Cohort.

 

Levels of prenatal oestriol, oestradiol, oestrone and oestrone sulphate were significantly elevated, on average, in the 98 foetuses who later developed autism, compared to the 177 foetuses who did not. Interestingly, high levels of prenatal oestrogens were more predictive of autism development than were high levels of prenatal androgens (such as testosterone). Contrary to popular belief that associates oestrogens with feminisation, prenatal oestrogens have effects on brain growth and masculinise the brain in many mammals.

 

Genetics is a well-established primary cause for autism development, however the authors conclude that prenatal oestrogenic excess may interact with genetic predisposition to affect neurodevelopment.

 

It is not known whether these elevated hormones come from the mother, the baby or the placenta. The next step should be to study all these possible sources and how they interact during pregnancy.

 

Of note, the team cautioned that these findings cannot and should not be used to screen for autism. ‘We are interested in understanding autism, not preventing it’, added Professor Baron-Cohen, the lead author of the study.

 

In summary, scientists demonstrated that prenatal oestrogens are elevated in boys who later developed autism. This supports their previous finding of elevated prenatal steroidogenesis in the same cohort, together adding weight to the prenatal steroid theory of autism. Further, high levels of prenatal oestradiol contribute to a greater degree to autism likelihood than other prenatal sex steroids, including testosterone.

 

As I ended my previous article on the cause of autism, whether it be genetics or environment, the aetiological basis is likely to be during foetal development. Thus, a person with autism is born with autism.

A new large-scale Danish study concluded that the measles, mumps and rubella (MMR) vaccine does not increase the risk of autism, even in susceptible children. Once again, no links are found.

 

The study that sparked the storm

Andrew Wakefield’s famous study, published in 1998, first described a link between autism and the MMR vaccine. A flurry of fear among the public has since found no rest.

However, the evidence of that study is poor and circumstantial at best. There is no attempt made to show a proven mechanism of how the vaccination process could or did lead to the degeneration of behaviour observed. While there is undoubtedly a trend in their data, the authors are vastly overstating the likelihood that this could be a true causal association.

Importantly, this study does not include controls, such as patients with autism that were not vaccinated, neither does it suggest that this type of even-handed study should be done. It appears that the authors have ‘chosen’ a set of patients with autism to reach a presupposed conclusion. This is clear bias and should be accounted for.

Further, the paper was soon retracted as Wakefield was found guilty of fabricating data and violating ethical protocols. The confidence of the authors in their conclusions is thus unjustified.

Despite there being no convincing evidence that the MMR vaccine causes autism, there is an underground faction of concerned parents who believe that it does. One reason for this may be that ∼50,000 children per month, in Britain alone, receive the MMR vaccine between ages 1 and 2 years. This is at a time when autism typically presents. Thus, coincidental associations are inevitable.

 

The data are in, again

A new large study yet again found no association between the MMR vaccine and autism.

The researchers followed 657,461 Danish children born between 1999 and 2010 and compared autism rates in those who had received the MMR vaccine against those who did not.

In emphatic language they write, ‘The study strongly supports that MMR vaccination does not increase the risk for autism, [and] does not trigger autism in susceptible children’.

In further analyses, they also looked for links between vaccinations other than MMR and autism; again, they found none.

One of the study’s main strengths is the large number of individuals included in the analysis. As the authors write, the study’s size allowed them to conclude that ‘even minute increases in autism risk after MMR vaccination are unlikely’.

 

So, what causes autism? 

The aetiological basis of autism is predominantly genetic, and the apparent rise in diagnosis has more to do with increased awareness of the condition and changes in the diagnostic criteria. Nevertheless, while mutations in some genes are strongly implicated in autism, most associated variants confer modest increases in risk.

These genetic variants of small effect sizes can have a significant impact when present in certain combinations, or even lower the threshold of one acquiring the condition with exposure to environmental risk factors.

The answer to what causes autism is unlikely to reside solely in genetics. Recent studies suggest that environmental factors can cause autism, but this is most likely to occur in utero (during pregnancy). This is important because some parents are concerned that things such as high pollution or vaccines cause autism postpartum.

Regardless, the heritability of autism is estimated to be more than 90%. This means that more than 90% of the cause of autism is due to genetics.

 

Conclusion

With the continued generation of high-quality empirical evidence, the fears surrounding vaccines might, one day, be eradicated once and for all.

The bottom line is that whatever the cause of autism may be – genetic or environmental – it is likely to take effect during foetal development. Thus, a person with autism is born with autism.