Mitochondrial Disease and Autism: How common?

Earlier this year, reports that the US Federal Court of Claims had conceded that vaccines had contributed to the onset of autistic symptoms in the case of Hannah Poling led to much speculation and debate about (1) if mitochondrial disorders could be linked to autism and (2) how common mitochondrial disorders might be among autistic children. A number of experts on mitonchondrial disorders met in June to discuss the “controversial case” of Hannah Poling. An article in the November 26th PLoS One entitled Mitochondrial Disease in Autism Spectrum Disorder Patients: A Cohort Analysis investigates the medical records of 25 patients with a primary diagnosis of ASD by DSM-IV-TR criteria. These children were later determined to have “enzyme- or mutation-defined mitochondrial electron transport chain (ETC) dysfunction”; of these, 24 had “one or more major clinical abnormalities uncommon in idiopathic autism” and 21 had “histories of significant non-neurological medical problems.”

“Idiopathic autism” has “become somewhat of a catch-all phrase where a cause, most often genetic, is unknown,” according to the Not Mercury blog. The “non-neurological medical problems” noted in 21 of the 25 participants in the PLoS One  study were primarily gastroinesstinal dysfunction; some also had “pancreatic dysfunction or liver disease–gastrointestinal disorders that are rare in persons with ASD.” Indeed, the authors later state that “non-neurological disorders were nearly universal in our patients.” Also noted was an “increased frequency of prenatal and perinatal complications ….. in children with ASD” and a “high frequency of multiple gestation births.” And, while autism spectrum disorders are diagnosed at a much higher rate in males than in females, in the cohort studied in the PLoS One article, there was an equal number of males and females. In regard to a link between vaccines and mitochondrial disorders, only one of the 25 participants was reported as having “autism/neurodevelopmental deterioration appeared [following] vaccination,” but “such timing does not prove causation.”

Among the conclusions of the researchers was that “careful clinical and biochemical assessment identified clinical findings” in the 25 participants that differentiated them from children with idiopathic autism; accordingly, it is possible that a “disturbance of mitochondrial energy production as an underlying pathophysiological mechanism” might be found in a “subset” of autistic individuals. How common, indeed, are mitochondrial disorders among autistic individuals—are they widely prevalent or a subpopulation? Journalist David Kirby writes about the study in the Huffington Post and seeks to argue that they are not so rare.

Much of the energy fueling the past several months’ discussion about mitochondrial disorders and autism has stemmed from an ongoing interest in identifying a biological cause for autism. The researchers of the PLoS One article note that they found “diverse and complex developmental, neurological, and medical phenotypes of persons with mitochondrial autism”:

Although many children with ASD exhibit some degree of hypotonia, most attain their early gross motor milestones on time. In contrast, 64% of our patients were delayed in attaining early developmental milestones and 32% were five or more standard deviations later than the mean in walking independently. In addition, although regression has been reported to occur in approximately one third of autistic children, typically before age three years, 40% of our patients demonstrated unusual patterns of regression–either repeated regressions, regressions involving losses of gross motor function, and/or regressions after age three years.

I note this mention of hypotonia—decreased muscle tone—and regression. In accounts of the onset of autistic symptoms in Hannah Poling, it was noted that she “refused to walk” and that she “lost her ability to speak” and showed other signs of regression in her development. On a more personal note, my son Charlie was very delayed in meeting all of his gross motor milestones as an infant and toddler. He rolled over, sat up, and walked late—he was 15 months when he was able to walk. He never “regressed” as he often seemed to take a very long time to acquire skills that other children his age had long had. Charlie was often said to be hypotonic when he was younger.

I have to say “was” because it’s been a long time since I heard the word used in reference to Charlie. Charlie learned to swim at 6, around the same time that Jim got him going on his bike (with and soon without training wheels, Jim soon had Charlie pedaling all over the sidewalks and then into the street). Charlie walks for miles with us now, and bikes for even more, and probably would swim for miles in the ocean, if we let him (no we are not). Friday afternoon he pedaled so fast that Jim could barely keep up with him at some moments. Hypotonic no more, Charlie’s in shape.

The authors of the PLoS One study conclude:

Overall, our results demonstrate substantial clinical heterogeneity of individuals with co-occurring autism and defects of mitochondrial oxidative phosphorylation, nearly all of whom we found to be clinically distinct from children with idiopathic autism. The data do not exclude the possibility of persons with isolated autism having a disorder of oxidative phosphorylation–in fact, one of our patients did not have any major clinical features that distinguished her from typical autism. In addition, it is possible, if not likely, that a still broader clinical, biochemical and genetic spectrum of mitochondrial autism exists.

………………The data reported here, and other cases of mitochondrial autism, argue that defective mitochondrial oxidative phosphorylation is an additional pathogenetic basis for a subset of individuals with autism.

The reasons that children may have “co-occurring autism and defects of mitochondrial oxidative phosphorylation” arise from a number of varying causes and much more–”a still broader clinical, biochemical and genetic spectrum of mitochondrial autism”—remains to be explored. It’s suggested that such cases of mitochondrial autism are a “subset,” whose size remains to be determined.