Homocysteine is an amino acid involved in methylation and sulfur amino acid metabolism. Elevated homocysteine levels are often interpreted as a marker of impaired methylation capacity and metabolic stress. Homocysteine is normally converted to other amino acids through pathways that require folic acid, vitamin B₆, and vitamin B₁₂. When these nutrients are insufficient or when these pathways are impaired, homocysteine can accumulate.
Some research has reported higher homocysteine levels in children with autism spectrum disorder (ASD). A study published in the Acta Biochimica Polonica (2011; 58(1):31–34) compared urinary homocysteine levels in 34 children with ASD and 21 neurotypical children. The researchers found that children with ASD had significantly higher urinary homocysteine levels compared with controls (2.36 vs. 0.76).
The authors suggested that elevated homocysteine levels in these children may reflect differences in folate- and B-vitamin–dependent metabolic pathways. These findings were observational and do not establish causation, but they are consistent with research exploring methylation and nutrient metabolism in ASD.
