Thimerosal Exposure and the Role of Sulfation Chemistry and Thiol Availability in Autism

Abstract

Autism spectrum disorder (ASD) is a neurological disorder in which a significant number of the children experience a developmental regression characterized by a loss of previously acquired skills and abilities. Typically reported are losses of verbal, nonverbal, and social abilities. Several recent studies suggest that children diagnosed with an ASD have abnormal sulfation chemistry, limited thiol availability, and decreased glutathione (GSH) reserve capacity, resulting in a compromised oxidation/reduction (redox) and detoxification capacity. Research indicates that the availability of thiols, particularly GSH, can influence the effects of thimerosal (TM) and other mercury (Hg) compounds. TM is an organomercurial compound (49.55% Hg by weight) that has been, and continues to be, used as a preservative in many childhood vaccines, particularly in developing countries. Thiol-modulating mechanisms affecting the cytotoxicity of TM have been identified. Importantly, the emergence of ASD symptoms post-6 months of age temporally follows the administration of many childhood vaccines. The purpose of the present critical review is provide mechanistic insight regarding how limited thiol availability, abnormal sulfation chemistry, and decreased GSH reserve capacity in children with an ASD could make them more susceptible to the toxic effects of TM routinely administered as part of mandated childhood immunization schedules.

A two-phase study evaluating the relationship between Thimerosal-containing vaccine administration and the risk for an autism spectrum disorder diagnosis in the United States

“…These studies have yielded significant pathology or clinical symptoms in mice, rats, hamsters, and monkeys that are consistent with those observed in ASD following exposure to Thimerosal-containing vaccines mimicking the 1990s US routine childhood vaccination schedule [9]. …”

“…Many previous studies reveal children diagnosed with ASD have limited thiol availability and decreased glutathione reserve capacity, deficits which make them more susceptible to the toxic effects of Hg exposure from administration of Thimerosal-containing vaccines [9]. …”

A longitudinal cohort study of the relationship between Thimerosal-containing hepatitis B vaccination and specific delays in development in the United States: Assessment of attributable risk and lifetime care costs

“…Typically, nominal concentrations of Thimerosal present in infant vaccines ranged from 0.005% to 0.01% (12.5 lg Hg/0.5 mL vaccine dose or 25 lg Hg/0.5 mL vaccine dose) [4]. Infants may have been exposed to bolus doses of organic Hg nominally ranging from 12.5 lg Hg to 62.5 lg organic Hg, collectively totaling up to nominally 200 lg organic Hg from Thimerosal-containing childhood vaccines during the first 6 months of life, representing >50% of all Hg exposure when considering environmental sources of Hg [4].…”

Mercury in vaccines: A review

“…As discussed earlier, thiomersal exposure has been linked with the diagnosis of Autism, Hyperkinetic syndrome of childhood, Developmental delay and other Neurodevelopmental disorders in several studies [27][28][29][30][31]. Increased vulnerability to this preservative as a result of abnormality of chemical defence mechanisms has been reported in children with ASD [33]. Low birth weight and/or preterm babies are more susceptible to the risk of ethylmercury exposure from TCVs [32].…”

“…Another factor that may contribute to higher mercury levels is the reduced body mass of preterm babies. A review article has shown evidence of abnormal sulfation chemistry, limited thiol availability, and decreased GSH reserve capacity in children with ASD making them more vulnerable to the toxic effects of thiomersal injected along with vaccines [33]. Other literature reviews have also reported a significant link between ethylmercury exposure from thiomersal in vaccines and neurotoxic effects in humans [1,34].…”