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Wednesday, 24 April 2013

Spinocerebellar Ataxia (SCA) and Autism

Reviewing the literature on autism, various terms are used to classify the various shades of autism.-

·         Autism

·         High Functioning autism

·         Asperger’s syndrome

·         Autistic Spectrum Disorder (ASD)

 
The trend coming from the US is to classify all the disorders as a single disorder, and then by widening the definition, draw in an even greater pool of subjects; hence the so-called autism epidemic.

This is extremely un-scientific and indeed unhelpful.  Autism is just a collection of observable and indeed measurable behaviors.  The extent to which a subject is affected by each type of behavior varies wildly.

When a patient goes to his doctor, an initial investigation might involve taking temperature, measuring pulse, examining ear, nose and throat.  The doctor does not simply conclude the patient is sick; he has to look for a specific combination of symptoms and measurable variables and make a specific diagnosis.

Now consider a rare brain disorder, Spinocerebellar Ataxia (SCA).

SCA affects about 0.025% of the population.  Moderate to severe autism affects about 0.3% of the population.  We can say that autism is 12 times more prevalent than SCA, or if we use the latest American definition and use CDC data we would say that autism is 40 times more prevalent than SCA.

Yet SCA seems far better understood and thoroughly researched than ASD.  You need go no further than Wikipedia, to see that 60 sub-types have been identified.  The disease itself is a progressive and degenerative but each sub-type has a unique cause and indeed a unique prognosis.  Usually the diagnosis comes after examination by a neurologist, which includes a physical exam, family history, and testing such as an MRI of the brain and spine and a spinal tap.

The prognosis is not good for any of the 60 types, but at least in Japan the pharmaceutical industry did develop a drug therapy.  Somewhat bizarrely, this therapy is unavailable outside Japan.  Equally bizarre is that a drug like Prozac, which is commonly prescribed to children in the US with ASD, is illegal in Japan.

The major sub-types of SCA are shown in the table.  




Implications of multiple types of autism

If autism also has many variants, it likely will also have many different causes and therefore likely have different pharmacological interventions.

This has a massive impact on clinical trials for possible therapies.

The fact that a subgroup of 20% might respond to a treatment but 80% do not, should perhaps be viewed as a success and not a failure.

Drug therapies must be related to a specific biological failure.

If, as seems likely, the same aberrant behaviour can be caused by more than one biological failure, then researchers have to be very much more wary how they conduct their clinical trials and more importantly how they interpret the results.

 

 





 

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