Circulating thyroid hormones and metabolites in children with autism spectrum disorder.

Researchers compared thyroid hormone levels between 788 autistic children and 301 non-autistic children. They found autistic children had slightly lower levels of several thyroid hormones and related substances in their blood. While these differences were measurable, they were small and it's unclear what this means for the children's health or development.

This cross-sectional study examined thyroid hormone levels and metabolites in 788 autistic children compared to 301 non-autistic children (mean age ~7.6-7.8 years). Using advanced laboratory techniques, researchers found that autistic children had significantly lower levels of free T4, free T3, total T4, and total T3 hormones, along with decreased thyroid metabolites 3,5-T2 and 3,3'-T2, while T0 levels were higher. However, TSH levels (thyroid stimulating hormone) were similar between groups, and the observed differences, while statistically significant, were described as small. The study suggests altered thyroid hormone metabolism in autism but requires further investigation to understand clinical significance.

While thyroid hormone differences exist between autistic and non-autistic children, the small magnitude and unclear clinical significance suggest routine thyroid screening protocols may remain unchanged. Further longitudinal research is needed to understand if these differences impact development or treatment outcomes.

Cross-sectional design cannot establish causality. The clinical significance of the small observed differences is unclear. The study doesn't address whether these differences impact autism symptoms or development.

Thyroid hormones affect neurological development and function, but detailed studies of thyroid hormones and metabolites in autism are lacking. To characterize thyroid function and metabolism in autistic children. This cross-sectional study compared 788 autistic children (mean age 7.6 ± 3.9 years, 78% male) with 301 non-autistic children (mean age 7.8 ± 4.0 years, 48% male; comprising 215 (71.4%) non-autistic siblings of participants and 86 (28.6%) unrelated individuals). Plasma TSH, free T4 (FT4) and free T3 (FT3) were measured by automated immunoassay, and total T4, total T3 and thyroid hormone metabolites by customized liquid chromatography-tandem mass spectrometry (LCMS/MS).

Regression analyses were adjusted for age and sex. TSH concentrations were similar in autistic and non-autistic children (median 2.3 vs 2.1 mU/L, P = 0.64). FT4 was significantly lower in autistic children (18.4 vs 18.7 pmol/L, P = 0.0003), as was FT3 (7.0 vs 7.1pmol/L, P<0.0001), with no significant difference in the FT4:FT3 ratio (P = 0.24). Total T4 was lower in autistic children (178 vs 194 nmol/L, P = 0.0026, as was total T3 (2.2 vs 2.4 nmol/L, P = 0.018), with no significant difference in the T4:T3 ratio (P = 0.099).

Two metabolites were significantly lower in autistic children: 3,5-T2 (0.010 vs 0.021 nmol/L, P<0.0001) and 3,3'-T2 (0.12 vs 0.16 nmol/L, P<0.0001), whereas T0 levels were higher (1.5 vs 1.1 nmol/L, P = 0.028). Circulating thyroid hormones and metabolites differ between autistic and non-autistic children, although the observed differences are small. The study demonstrates the utility of LCMS/MS for in-depth characterization of thyroid hormone economy, with potentially wide applications.