Autism Research: Distinguishing the good from the bad

Neuropathology is the subspecialty of pathology that studies biopsies or autopsy tissue from the nervous system. The tissue examined includes the central and peripheral nervous system, skeletal muscle and occasionally the eye. Traditionally, neuropathologists need to obtain an MD degree, followed by residency training in pathology, and finally 2-3 years of a fellowship in the particular subspecialty.

The curious fact is that many of the people doing neuropathological work within autism research have none of the above listed credentials or training. If lucky, some published researchers within the field will have graduate degrees in anatomy. At worse, they come from other disciplines quite removed from neuropathology such as psychiatry or even physiology. It is therefore not surprising that many of the reported findings in autism have not been reproduced or appear to offer contradictory findings. How do you separate the wheat from the shaft?

Not all tissue is the same. The likelihood of degradation is high if an inordinate amount of time transpires after death before tissues are placed in fixative. It is therefore essential to consider those changes accrued to agonal conditions or how the brain was collected and distinguish them from core pathological process that mediate a particular disorder, e.g., autism. For a neuropathologist this is not difficult, for those without any training, such a distinction is impossible. It is for this reason that neuropathologists, before starting a study, judge the suitable of the available tissue. This will take into consideration whether the boundaries of cells (cytoplasm) are intact, whether structures characteristic of each cell are still present, and whether the genetic material in the nuclei is abnormally clumped.

The following comment was taken from a report from the Autism Tissue Program and the same relates to the presence of degradation in some of the tissue available for research:

“…it was very disappointing to discover that the majority of the brain samples showed extensive degradation and that no meaningful conclusions could be drawn from the experiments. If we had not decided to perform the autoradiography and the hemalum staining after the Western blot experiments, we would have not been aware that we were working with degraded tissue samples. Several research groups received the same brain samples that we got and because they did not perform brain sections, they did not realize the problem with the tissue quality and went on to publish their findings.” Catalina Betancur and Salah El Mestikawy, Université Pierre et Marie Curie, Paris France (Jane Pickett, ATP Report, 2010).

The comments relate the frustration of some investigators with the available brain tissue. The scarcity of adequate tissue makes the loss of many such specimens in a recent freezer meltdown all the more meaningful (https://corticalchauvinism.wordpress.com/2013/03/06/autism-banking-on-the-future-of-our-children/). More so, the comment raises concerns as the results of some reported articles claiming positive findings can be explained away by tissue degradation rather than by them being a useful pathological correlate to autism.

Another example where lack of expertise comes into play is from studies on brain weight/volume in autism. It is claimed that, on average, brains of autistic individuals are larger than those of neurotypicals. Although this may be the case, some of the conclusions derived from neuropathological studies are erroneous. One heavily cited series reported three massive brains that skewed their results. The presence of edema without any herniation suggests a postmortem artifact. One of the brains even showed signs of putrefaction; being soft to the touch and having multiple pockets of bacteria within the tissue.These brains should not have been included in any study.

Taking as an excuse the dearth of tissue available one particular investigator has joined together into a series brains that have been collected and processed by different laboratories under different conditions. Tissues were sectioned at different thicknesses and then quantitated for morphometric parameters. Although the findings have been publicized this is far removed from optimal science.

ischemia reperfusion injury
The figure illustrates the many changes that occur after ischemia-reperfusion injury.

In a previous blog I have already mentioned how many so-called inflammatory changes in postmortem tissue may reflect a type of injury acquired close to death (i.e., ischemia reperfusion injury) (https://corticalchauvinism.wordpress.com/2013/02/04/inflammation-and-autism/). These types of brains should have never been the object of study. The changes seen in them are not characteristic of autism but artifacts of long postmortem intervals, of the way the brains were collected or fixed, and of previous insults (e.g. ischemia-reperfusion injury). The problem therefore is not having a small number of neuropathological changes reported in the literature, rather, we have too many! Unfortunately many of these changes mislead researchers from pursuing true findings.

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