摘要Background Autism spectrum disorder(ASD)is a complex group of neurodevelopmental disorders.Research has highlighted a close association between the retinoic acid(RA)signaling pathway and ASD.This study investigates alterations in the vitamin A(VA,retinol)to RA metabolic pathway in children with ASD and speculates on the underlying reasons for these changes.We propose a subtype characterized by downregulated RA signaling in ASD,laying the groundwork for precise diagnosis and treatment research.Methods We included 489 children with ASD and 280 typically developing(TD)children.Those with ASD underwent evaluations of core symptoms and neuro-developmental levels,which were conducted by professional developmental behavior physicians using assessment scales.Serum VA and all-trans RA(atRA)levels were determined by high-performance liquid chromatography and ultra-high-performance liquid chromatography-tandem mass spectrometry.The expression levels and concentrations of enzyme molecules such as retinol dehydrogenase 10 were assessed using quantitative polymerase chain reaction and enzyme-linked immunosorbent assay.Results Children with ASD exhibited reduced serum atRA,accompanied by a downregulation of atRA synthesis enzymes.The reduction in serum atRA levels was linked not only to VA levels but also to the aberrant expression of metabolic enzymes responsible for atRA.Furthermore,the serum atRA levels in children with ASD were more strongly correlated with core symptoms and neurodevelopmental levels than VA levels.Conclusion Children with ASD exhibited a dual regulation of reduced serum atRA levels,influenced by both VA levels and abnormal expression of atRA metabolic enzymes.