Toxicity biomarkers in autism spectrum disorder: A blinded study of urinary porphyrins

Background: Recent studies suggest that children diagnosed with an autism spectrum disorder (ASD) have significantly increased levels of urinary porphyrins associated with mercury (Hg) toxicity, including pentacarboxyporphyrin (5cxP), precoproporphyrin (prcP), and coproporphyrin (cP), compared to typically developing controls. However, these initial studies were criticized because the controls were not age- and gender-matched to the children diagnosed with an ASD. Methods: Urinary porphyrin biomarkers in a group of children (2-13 years of age) diagnosed with an ASD (n = 20) were compared to matched (age, gender, race, location, and year tested) group of typically developing controls (n = 20). Results: Participants diagnosed with an ASD had significantly increased levels of 5cxP, prcP, and cP in comparison to controls. No significant differences were found in non-Hg associated urinary porphyrins (uroporphyrins, hexacarboxyporphyrin, and heptacarboxyporphyrin). There was a significantly increased odds ratio for an ASD diagnosis relative to controls among study participants with precoproporphyrin (odds ratio = 15.5, P < 0.01) and coproporphyrin (odds ratio = 15.5, P < 0.01) levels in the second through fourth quartiles in comparison to the first quartile. Conclusion: These results suggest that the levels of Hg-toxicity-associated porphyrins are higher in children with an ASD diagnosis than controls. Although the pattern seen (increased 5cxP, prcP, and cP) is characteristic of Hg toxicity, the influence of other factors, such as genetics and other metals cannot be completely ruled out.