Elevated Urinary Levels of a Known Compound Derived From the Gut Flora in a Subgroup of Autistic Children

Background: In recent years, several studies have reported gastrointestinal abnormalities accompanied by increased gut permeability in a consistent subgroup of autistic patients. Other studies have also unveiled an excess of unusual bacterial strains in the gut flora of autistic individuals.
Objectives: This study aims at measuring the urinary amounts of a known compound which cannot derive from human metabolism, but can instead exclusively come from the catabolism of the bacterial wall of strains previously shown to be overrepresented in the gut flora of many ASD patients. This compound could also derive from exposure to hydrocarbons, requiring controls for levels of active and passive smoking.
Methods: Urines were collected from 59 ASD patients and 59 age- and sex-matched controls, recruited from different clinical centers located in Central and Northern Italy (age range: 2-18 years; M:F ratio = 3:1). Compound concentrations were measured by HPLC. We also measured levels of cotinine, a urinary metabolite of nicotine, using a specific ELISA assay.
Results: All subjects were included, since we found no evidence of active smoking and the urinary amounts of the compound were totally unrelated to urinary cotinine levels. We found a significant difference in the concentration of the compound between autistics and controls (123.5 ± 12.8 vs 91.2 ± 8.7 μg/ml, Student-t = 2.091, 116 df, P<0.05). Moreover, this increase was interestingly limited to ASD patients up to 7 years old (134.1 ± 20.1 vs 70.3 ± 6.7 μg/ml, Student-t = 2.922, 60 df, P<0.01), whereas no difference at all was found between patients and controls aged 8 or older (111.0 ± 14.5 vs 112.7 ± 15.5 μg/ml, Student t= -0.81, 54 df, P=0.936). Before age 8, levels above 175 mg/ml were found in 8/32 (25%) ASD patients vs 0 controls (P=0.0046), whereas levels above 140 mg/ml were detected in 9/32 (28.1%) ASD patients vs 1/32 (3.1%) controls (P=0.0127).
Conclusions: Our results are consistent with the existence of a subgroup including approximately 25-30% ASD patients carrying an abnormal gut flora and/or possibly increased gut permeability. In young children, this compound could contribute to a panel of biochemical and genetic measures able to estimate autism risk or to support clinical diagnoses, whereas patterns of urinary excretion appear to normalize after age 7. Since this compound could conceivably exert behavioral effects, we are now assessing whether its urinary concentrations correlate with signs or symptoms of autism. Behavioral studies on rodents are also under way.