I have received many emails about yesterday’s post on the CDC autism prevalence study. I thought I would spend some time to briefly address 3 specific issues.

1. Prevalence Rates and Home Schooling.

I received a thoughtful email about the impact of home schooling on the CDC prevalence rate and autism research in general, given that many children with ASDs may be home schooled. Here is my response: Read More

On Monday I discussed a study examining the link between parental vaccination refusal and childhood pertussis. I was most interested in discussing the process by which parents reach the decision to reject vaccine recommendations. In theory, I assume most parents reach such a decision after weighting the risk of vaccines against the risk of refusing the vaccines, and I questioned whether parents have the necessary information to properly weight these risks.

While reading the same issue of the journal Pediatrics, I came across a related study that examined the factors that predict whether a mother intended to vaccinate her daughter against HPV. I was very interested in this study because it could shed light into the decision processes behind parental refusal to vaccinate. That is, is the decision to refuse vaccination only a function of weighting risks vs. benefits? Or is such a decision also associated with other factors that may not be related to the issue of vaccine safety at all? Read More

Pertussis is a highly contagious and potentially deadly respiratory infection that affects mostly children in the developing world. The low prevalence of pertussis in industrialized nations is partly due to the effectiveness of the pertussis vaccine. However, several studies have indicated that the rates of pertussis in the US have significantly increased during the last decade, likely due to a parallel decrease in vaccinations, as parents have become increasingly worried about vaccine safety. But is this true? Are children of parents who decline the pertussis vaccine at higher risk for acquiring this disease?

The journal of the American Academy of Pediatrics recently published a study that examined the association between vaccination refusal and pertussis infections in Colorado. In this study, the authors conducted a case-control examination of children between 2 months and 18 years who were members of a large health plan (Kaiser Permanente Colorado). The study included 156 cases of pertussis and 595 control non-pertussis children. Read More

The New England Journal of Medicine just published a placebo-controlled, randomized, double-blind study of a vaccine (recombinant CMV envelope glycoprotein B with MF59 adjuvant) in the prevention of maternal infection with with cytomegalovirus (CMV) during pregnancy.

Infection with CMV is major cause of auditory and cognitive impairment in newborns. CMV is actually very common, but when acquired during pregnancy the risk to the developing fetus is very high. Approximately 27,000 CMV infections among pregnant women occur in the United States each year Read More

A review of: D GEIER, J KERN, C GARVER, J ADAMS, T AUDHYA, R NATAF, M GEIER (2008). Biomarkers of environmental toxicity and susceptibility in autism☆ Journal of the Neurological Sciences DOI: 10.1016/j.jns.2008.08.021

One bio-social model of the etiology of autism suggests that a genetic predisposition, in the form of limited ability to remove toxins from the body (e.g., mercury), combined with exposure to such toxins, leads to an increased risk for developing autism. As I previously described in this study, researchers have examined urinary porphyrins as a measure of mercury exposure, and some studies have found increased levels of porphyrins in children with autism. In this study, the authors examined urinary porphyrin metabolites (a proposed measure of heavy metal toxicity) and plasma sulfates (a proposed measure of detoxification capacity) among children with autism.

The sample included 28 children between the ages of 2 and 16 recruited from the Dallas/Fort Worth community. These children had a diagnosis of autism (Childhood Autism Rating Scale scores above 30). This group was categorized into a mild (CARS
38.5) autism. Blood and urine samples were collected for analysis. A laboratory standard control sample of typically developing children was also included in the plasma analysis only.

The mild ASD group had significantly lower ratios of key porphyrin levels when compared with kids with severe ASD. The following group means are statistically significantly different from each other:

Porphyrin
Pentacarboxyporphyrin
MILD ASD = 4.92±2.79 VS. SEVERE ASD = 6.0±1.58

Precoproporphyrin
MILD ASD = 17.3±8.9 VS. SEVERE ASD = 24.05±7.28

Ratios:
Pentacarboxyporphyrin/uroporphyrins I and III
MILD ASD = 0.19±0.06 VS. SEVERE ASD = 0.27±0.08

Precoprophyrin/uroporphyrins I and III
MILD ASD = 0.68±0.28 VS. SEVERE ASD = 1.09±0.36

Coproporphyrins I and III/ uroporphyrins I & and III
MILD ASD = 9.54±2.97 VS. SEVERE ASD = 12.64±3.47

(Precoproporphyrin+ pentacarboxyporphyrin) / (uroporphyrins I & and III+ heptacarboxyporphryin)
MILD ASD = 0.73±0.26 VS. SEVERE ASD = 1.1±0.29

The authors concluded that increased urinary porphyrin metabolites were associated with more severe autism based on CARS scores. Urinary porphyrin are believed to represent mercury toxicity.

Furthermore, the authors found significantly lower levels of plasma sulfates (Plasma cysteine, Plasma reduced glutathione, Plasma oxidized glutathione) among children with autism when compared to typically developing kids. Decreased sulfation (low plasma levels of sulfates) can indicate limited detoxification capacity, especially of heavy metals such as mercury.

In conclusion, the study presents some compelling evidence regarding differences in urinary porphyrin metabolites between kids with mild and severe autism symptoms, as well as differences in plasma sulfates between kids with autism when compared to neurotypical kids. This is consistent with the author’s theory that mercury exposure plays a role in autism. However, given the controversy regarding the mercury-autism association, I would like to clarify that these results do not indicate that mercury causes autism. Yes, it is possible that mercury toxicity and reduced detoxification capacity plays a role in autism, both, in the onset and severity. However, it is also possible that Autism itself results in reduced detoxification capacity and mercury toxicity via other mechanisms, but that such toxicity is not associated at all with the development of the disorder. For example, erythrocyte sedimentation rate and C-reactive protein are tests used in arthritis. Atypical results on these tests are found in people with arthritis. Yet, neither one is related to any of the proposed causes of arthritis, and instead reflect a consequence of the disorder itself (inflammation).