Monday, 21 July 2014

Autism and asthma yet again

"Asthma is approximately 35 % more common in autistic children".

Pipe down @ Wikipedia 
That was the finding reported by Stanley Kotey and colleagues [1] based on their analysis of the 2007 National Survey of Children's Health (NSCH) dataset, a resource looking at "the physical and emotional health of children ages 0-17 years of age" resident in the United States. I don't intend to dwell too much on the Kotey findings aside from pointing out: (a) the reported prevalence of autism came in at 1.8% which is not a million miles away from the latest US estimate made by the CDC and, (b) although the unadjusted odds ratio (OR) for asthma in cases of autism was 1.35 (CI: 1.18-1.55), the adjusted OR taking into account factors such as "age, gender, body mass index, race, brain injury, secondhand smoke and socio-economic status" dropped down to 1.19... so perhaps it was more accurate to conclude that asthma is approximately 20% more common in kids with autism. Oh and that OR and relative risk might not necessarily be one and the same [2].

The NSCH is a valuable resource which provides snapshots for lots of different aspects of child health and wellbeing (see here). A quick trawl of the sections pertinent to an autism and/or asthma diagnosis (see section 2 here) reveals how information about diagnosis is arrived at. I was taken by the fact that questioning about an autism spectrum disorder (ASD) diagnosis was "applicable for ages 2-17 years only" which perhaps ties into some of the issues raised in other papers when it comes to early diagnosis.

Asthma and autism is a topic not totally unfamiliar to this blog (see here). The quite recent paper from Tsai and colleagues [3] covered in a previous post (see here) detailing how asthma might be a risk factor for autism puts the Kotey findings into some potential context albeit not necessarily with the same directional association. The paper from Chen and colleagues [4] likewise also discussed in another post (see here) also implicates comorbidity (ADHD in that case) as a potential confounding variable bearing in mind the estimated rates of ADHD in cases of autism (see here).

When it comes to the hows and whys of any relationship between asthma and autism, a rather large void starts to appear outside of any link just being due to coincidence [5]. "[The] Autism-secondhand smoke interaction was insignificant" kinda suggests that tobacco smoke filled houses and cars were probably not a primary reason for any connection. Given what is known about asthma - a chronic lung condition characterised by inflammation of the airways - one might look to something like immune function as being a commonality between the conditions especially in light of recent meta-analyses with autism in mind. A couple of years back I did a sort of focus on some of the work from Kevin Becker (see here) including his paper on the hygiene hypothesis [6] (open-access here). I'm not necessarily saying that this is the primary connector, merely that the interaction between immune functions and environment might have some role to play. I might add that all the recent chatter on air pollution and autism (see here and see here and most recently here) might also be something to look at with further assiduity. Oh, and one might also think about certain medicines as perhaps being important to this relationship too (see here).

I would close with a last sentence from Kotey et al: "screening may be an efficient approach to reduce risk of morbidity due to asthma". In other words, asthma is yet another comorbidity for which a diagnosis of autism seemingly carries no protection, and the onus is on professionals to reduce any further health inequality...

So: Ben E King and Stand By Me. "Chopper! Sic'em, boy!"

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[1] Kotey S. et al. Co-occurrence of Autism and Asthma in a Nationally-Representative Sample of Children in the United States. J Autism Dev Disord. 2014 Jul 6.

[2] Davies HT. et al. When can odds ratios mislead? BMJ. 1998 Mar 28;316(7136):989-91.

[3] Tsai PH. et al. Increased risk of autism spectrum disorder among early life asthma patients: An 8-year nationwide population-based prospective study. Research in Autism Spectrum Disorders. 2014; 8: 381-386.

[4] Chen MH. et al. Asthma and attention-deficit/hyperactivity disorder: a nationwide population-based prospective cohort study. J Child Psychol Psychiatry. 2013 Nov;54(11):1208-14.

[5] Mrozek-Budzyn D. et al. The frequency and risk factors of allergy and asthma in children with autism--case-control study. Przegl Epidemiol. 2013;67(4):675-9, 761-4.

[6] Becker KG. Autism, asthma, inflammation, and the hygiene hypothesis. Med Hypotheses. 2007;69(4):731-40.

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ResearchBlogging.org Kotey, S., Ertel, K., & Whitcomb, B. (2014). Co-occurrence of Autism and Asthma in a Nationally-Representative Sample of Children in the United States Journal of Autism and Developmental Disorders DOI: 10.1007/s10803-014-2174-y