passionless Droning about autism

Posts Tagged ‘Male / Female Ratio

Hello friends –

Whatever your take on the predominant cause of autism(s), your thoughts on the appropriateness, or inappropriateness of research allocations in the autism realm, one thing can’t be denied; collectively, a lot of researcher time and dollars have been poured into autism research.  We’ve learned some important things, some cool things, some confusing things, some obscure things, and some useless things.   But even with all of the resources we have applied towards understanding autism, one of the most curious unknowns is also one obvious to the most rudimentary observations, the persistently skewed male to female ratio, with a finding of three or four males to every female with autism.   It is one of the most vexing questions, almost taunting us with seeming obviousness, but consistently elusive.  It isn’t just autism, lots of other neurological conditions are similarly tilted, and in a bazillion animal models it seems an unfortunate fact that being born male simple predisposes you (or rat you) to a variety of things you’d rather not have. 

The ideas I have seen floated most frequently to explain this observation involve the effect of prenatal testosterone and the associated ‘extreme male brain’ theory, a loss of genetic backups to compensate for mixups, and synergistic effects of testosterone on chemicals, notably, mercury; explanations which I generally like a little, a little less, and almost not at all, respectively.  An idea I’ve floated a couple of times, but that seemed even less accepted (or, more likely, completely unnoticed), was that estrogen might be acting in a protective manner; as it is known to exhibit attenuate the effects of neuroinflammation and oxidative stress.  Indeed, it is starting to look like estrogen receptors are expressed in a large variety of situations salient to CNS processes.  

A few weeks ago, the same group that has published some immensely cool studies on epigenetics and brain proteins, genetic expression differentials within twin siblings with autism, and circadian rhythm alterations comes a paper which may give us insight into this question, so that is pretty exciting.  Even cooler, it invokes a negative feedback loop in a complicated system and is built upon the foundation of several earlier studies on a protein implicated in lots of things we know are awry in autism.  That study is Sex Hormones in Autism: Androgens and Estrogens Differentially and Reciprocally Regulate RORA, a Novel Candidate Gene for Autism (full paper).  Here is the abstract:

Autism, a pervasive neurodevelopmental disorder manifested by deficits in social behavior and interpersonal communication, and by stereotyped, repetitive behaviors, is inexplicably biased towards males by a ratio of ~4:1, with no clear understanding of whether or how the sex hormones may play a role in autism susceptibility. Here, we show that male and female hormones differentially regulate the expression of a novel autism candidate gene, retinoic acid-related orphan receptor-alpha (RORA) in a neuronal cell line, SH-SY5Y. In addition, we demonstrate that RORA transcriptionally regulates aromatase, an enzyme that converts testosterone to estrogen. We further show that aromatase protein is significantly reduced in the frontal cortex of autistic subjects relative to sex- and age-matched controls, and is strongly correlated with RORA protein levels in the brain. These results indicate that RORA has the potential to be under both negative and positive feedback regulation by male and female hormones, respectively, through one of its transcriptional targets, aromatase, and further suggest a mechanism for introducing sex bias in autism.

The press release and google news cycle for this paper seemed to have been well ahead of the pubmed robot; Kev had a post on this study a few weeks before it hit pubmed with a postdate.  I generally skip out on the interest story/vaccine fairytale story/vaccine nightmare story/lost child nightmare story that is the google news autism feed, but in this case, it harbored a story on a paper that I was actually interested in.  In any situation, the paper landed in pubmed this morning, and is available in full via PLOS, so great stuff is available to us all.

The paper starts with some of the backstory, the ‘inexplicable’ male predominance in autism, some of the theories on why this might be the case, and most importantly, details on previous findings by this set of researchers on reduced levels of RORA in the CNS of people with autism, a protein with a great number of functions of interest to the autism community.

Together, these results link molecular changes in RORA in peripheral cells to molecular pathology in the brain of autistic individuals. These findings are particularly relevant to ASD as RORA is involved in several key processes negatively impacted in autism, including Purkinje cell differentiation, cerebellar development, protection of neurons against oxidative stress, suppression of inflammation, and regulation of circadian rhythm. Behavioral studies on the RORA-deficient staggerer (RORA+/sg) mouse, primarily used as a model to study ataxia and dystonia[13], further show that RORA is also associated with restricted behaviors reminiscent of ASD, such as perseverative tendencies, limited maze patrolling, anomalous object exploration as well as deficits in spatial learning.

It’s tough to find a protein with a greater key word hitlist for our population of interest than Purkinje cell differentiation, cerebellar development, protection from oxidative stress, suppression of inflammation, and regulation of the circadian rhythm.  In fact, I’d be shocked to find a protein touching so many fracture points that wasn’t found altered in the autism population; it makes too much sense within the framework of an entangled system and what we already know about the physiology of autism.   Remember that the previous paper found decreased RORA in the brain of people with autism; i.e., less of a protein that protects from oxidative stress, supports Purkinje cell development, and suppresses the inflammatory response.  A relative lack of RORA makes a depressingly good amount of sense. 

That being said, what makes the current paper so interesting is that they found the RORA is differentially, and inversely modulated by female and male hormones (i.e., testosterone and estrogen).  But even more insidiously, one of the downstream products regulated by RORA, aromatase, participates in the cleavage of testosterone to estrogen; the authors essentially describe a negative feedback loop.  It turns out, not only is RORA decreased in the CNS of autism, but so too is aromatase. 

We also show that one of the transcriptional targets of RORA is aromatase, which is a crucial enzyme in the biosynthesis of estrogen from testosterone. It is noteworthy that both RORA and aromatase proteins are decreased in the frontal cortex of autistic subjects, and that the level of aromatase protein is strongly correlated with the level of RORA protein in the brain tissues. We therefore propose that the reduction of RORA observed in autism is exacerbated by a negative feedback mechanism involving decreased aromatase level, which further causes accumulation of its substrate, testosterone, and reduction of its product, estradiol. Testosterone and estradiol respectively exhibit negative and positive feedback regulation of RORA expression as illustrated in Fig. 5, which summarizes the principal findings of this study. Thus, a deficiency in RORA in autistic brain is expected to be further aggravated by increased levels of testosterone due to suppression of aromatase, a transcriptional target of RORA.

This is pretty neat; it shows how simply being male can lead to the downregulation of a system with tendrils attached to a great number downstream processes we know to be disturbed in autism. 

I particularly liked that this paper established a chain of learning more, something I think we can all agree is a great idea.  Some of the people on this study have been plugging away with some interesting ideas for a while, all of which, I believe, are ancestors of these findings.  They had two really neat papers on genetic expression in autism twins with differential degrees of autism severity, both of which used genomic bioinformatic tools to understand which the genetic pathways were affected.  This is actually rather brilliant; they essentially leveraged the genetic uniqueness of the twins to gain more insight into which processes were being affected in autism by seeing which genes were differentially expressed in identical twins that manifested differently, using genetics to learn about what is happening a layer above the genome.  Next, the original RORA paper began to probe the mechanism by which the previously observed expression was achieved, they found that a particular protein, RORA, was overmethylated and consequently at depressed levels.  Another bioinformatic approach told them that RORA was a particularly attractive candidate for further evaluation based on its descendant interactions, and the association between RORA, aromatase, and sexual hormones appeared.  Beautiful.

All that coolness not withstanding, some of the articles I saw on this lacked the caution and nuance we ought to see with these kinds of findings; the paper was pretty clear that previous CNS studies hadn’t shown decreased RORA in all of their samples, just most of them.   This doesn’t answer all of our questions about the male dominance of autism, but we do know more than when this study was published, and that is pretty cool.   Hooray for knowledge.


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