Activity-dependent neuroprotective protein (ADNP) syndrome is a rare neurodevelopmental disorder caused by mutations in the ADNP gene, resulting in intellectual disability, developmental delay and autism spectrum disorder (ASD). Ketamine treatment has emerged as a promising therapeutic option for children with ADNP syndrome, showing safety and significant behavioral improvements. However, the underlying molecular perturbations caused by ketamine remain poorly described. We dissected the longitudinal effect of ketamine on the peripheral blood transcriptome of 10 individuals with ADNP syndrome. The blood transcriptome was profiled prior-to intravenous ketamine treatment (0.5mg/kg) and then again at five post-infusion timepoints: immediately post-infusion, day 1, week 1, week 2, and week 4. We show that a single low-dose infusion of ketamine triggers immediate and profound gene expression alterations, with specific enrichment of monocyte-related expression patterns. These alterations encompass diverse signaling pathways and co-expression networks, implicating up-regulation of immune and inflammatory-related processes and down-regulation of RNA processing mechanisms and metabolism. Notably, these changes exhibit a transient nature, returning to baseline levels 24 hours to 1 week after treatment. These findings advance our understanding of ketamine's molecular effects and provides a foundation for further research in elucidating its precise cellular and molecular targets. Moreover, the comprehensive assessment of ketamine-induced changes in ADNP syndrome contributes to the development of innovative therapeutic strategies for this challenging genetic disorder.