A Developmental Taxonomy of Autism and the Precision Timing of the Cheung Glutamatergic Regimen

Autism spectrum disorder is far more heterogeneous than traditionally assumed, with age at diagnosis reflecting distinct polygenic factors and fundamentally different developmental trajectories rather than simple differences in detection. What was previously described as a single two-stage synaptic course--early overgrowth followed by later depletion--now appears as two mechanistically separable subtypes. Early-diagnosed autism is characterised by a "Failure to Build," driven by deficits in mitochondrial function, ribosomal biogenesis, and cytoskeletal integrity during initial synapse formation. In contrast, late-diagnosed autism reflects a "Failure to Refine," arising from astrocyte dysfunction, complement-mediated over-pruning, and LRRK2 dysregulation during adolescent circuit remodelling, with strong transcriptomic convergence to ADHD. Against this backdrop, the Cheung glutamatergic regimen--a low-cost, orally available combination of dextromethorphan, a CYP2D6-inhibiting antidepressant, piracetam, and L-glutamine--is proposed as a ketamine-mimetic plasticity agent. The regimen is contraindicated in the early-diagnosed ("Build") subtype and in all children under approximately 10 years due to the risk of exacerbating bioenergetic stress and excitotoxicity. However, it may prove restorative in post-pubertal individuals with late-diagnosed autism and ADHD comorbidity by counteracting astrocyte dysfunction, excessive complement tagging, and LRRK2-related pruning dysregulation. This refined, subtype- and timing-specific framework carries important clinical implications and underscores the urgent need for biomarker-stratified randomised trials using synaptic density imaging and circuit-level outcomes. Keywords: autism heterogeneity, synaptic pruning, LRRK2, transcriptome-wide association study, glutamatergic enhancement, precision medicine.