Does circumcision cause autism?

Question

I got this on my Facebook wall this morning,

titled Circumcision, Pain, and the Risk of Autism Spectrum Disorders

The Findings

Across the entire sample, the risk of developing an ASD is 46% higher for circumcised boys than intact boys, and this is controlling for other birth and perinatal variables that were significant predictors (including birth factors which were independent predictors of ASDs, but that’s a discussion for another day), cultural background, birth year, and age. This was predominantly due to an increase in younger age diagnoses of ASDs (a diagnosis prior to age 5), for which the risk was 80% higher.

I am not sure about notability of source in this case but they are referring to study in Denmark with 300k boys...

Is circumcision causing autism?

Answer 1

The study you cite found an rate of autism of 6.3% among circumcised boys, and 1.5% among uncircumcised Danish boys. Another study also examined Danish boys, and got different results:

In our patient population, we found that 7.2% (95% CI 3.4–11.0) were diagnosed with autism spectrum disorder (ASD) as a concomitant disease (Table 3). A recent Danish study calculated the prevalence of ASD in Denmark to be 1.5% among boys, but a higher prevalence of ASD in other background population studies has recently been calculated to be in accordance with our findings.

In other words, 1.5% background is an abnormally low result.

A PubMed comment on the original study also points out that it misinterprets the mechanism that was being examined by one of its sources.

The finding in this cohort of 342,877 boys born between 1994 and 2003, that circumcised boys were more likely than intact boys to develop ASD before age 10 ... concurs with our study findings. It is, however, important to note that in our study we did not focus on the psychological consequences of the circumcision procedure as the causal ASD mechanism, rather we were using circumcision exposure as a proxy for the potential paracetamol (APAP, acetaminophen) exposure that may occur with the procedure. Our study aim was to explore at a population level the hypothesis of a relationship between paracetamol exposure and ASD.

A perplexing finding in this Frisch and Simonsen Danish study is a statistically significant association between circumcision and the development of autism in the cohort of boys ages 0-4 (hazard ratio (HR)= 1.80, 95% CI 1.25-2.60) while only a very weak association for the boys ages 5-9 (HR=1.15, 95% CI 0.75-1.77). This finding can be explained by the paracetamol hypothesis. The boys that were 5-9 years of age would have been born in 1999 or prior and, based on the timing of guideline development, would likely not have been exposed to paracetamol with the procedure, while the younger boys would likely have received analgesia.

Answer 2

A 2015 study in the Journal of the Royal Society of Medicine looked at the cases of autism spectrum disorder (ASD) in more than 340,000 boys born in Denmark between 1994 and 2003.

The researchers raised the possibility of a link between the psychological disturbances coming up from the pain of circumcision as a potential culprit.

“…painful experiences in neonates have been shown in animal and human studies to be associated with long-term alterations in pain perception, a characteristic often encountered among children with ASD. ASD is a complex group of neurodevelopmental disorders characterized by deficits in skills of reciprocal social interaction or communication with or without the presence of stereotyped behavior, interests and activities, and autistic children often have unusual reactions to sensory stimulation with either lowered or heightened sensitivity to noxious stimuli.”

However, a response was published later in the same year that rejected this hypothesis, and posing some other alternative hypotheses:

Could unnecessary general anaesthesia, not pain, have contributed to autism spectrum disorder?

[...]

Most likely, both autism spectrum disorder diagnosis and early circumcision reflect parental conscientiousness.