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The aromatic compound p-cresol (4-methylphenol) has been found elevated in the urines of Italian autistic children up to 8 years of age. The present study aims at replicating these initial findings in an ethnically distinct sample and at extending them by measuring also the three components of urinary p-cresol, namely p-cresylsulfate, p-cresylglucuronate and free p-cresol. Total urinary p-cresol, p-cresylsulfate and p-cresylglucuronate were significantly elevated in 33 French autism spectrum disorder (ASD) cases compared with 33 sex- and age-matched controls ( p < 0.05). This increase was limited to ASD children aged ≤8 years ( p < 0.01), and not older ( p = 0.17). Urinary levels of p-cresol and p-cresylsulfate were associated with stereotypic, compulsive/repetitive behaviors ( p < 0.05), although not with overall autism severity. These results confirm the elevation of urinary p-cresol in a sizable set of small autistic children and spur interest into biomarker roles for p-cresol and p-cresylsulfate in autism. [ABSTRACT FROM AUTHOR]

Several studies have described in autistic patients an overgrowth of unusual gut bacterial strains, able to push the fermentation of tyrosine up to the formation of p-cresol. We compared levels of urinary p-cresol, measured by high-performance liquid chromatography--ultraviolet, in 59 matched case-control pairs. Urinary p-cresol was significantly elevated in autistic children smaller than 8 years of age ( p < 0.01), typically females ( p < 0.05), and more severely affected regardless of sex ( p < 0.05). Urinary cotinine measurements excluded smoking-related hydrocarbon contaminations as contributors to these differences. Hence, elevated urinary p-cresol may serve as a biomarker of autism liability in small children, especially females and more severely affected males. [ABSTRACT FROM AUTHOR]