"SHANK3 deficiency alters early progenitor dynamics and reveals shared pathways with neurodegeneration"

Phelan-McDermid Syndrome (PMS), primarily linked to SHANK3 haploinsufficiency, presents with complex neurodevelopmental features, including developmental regression, whose underlying mechanisms are poorly understood. This study investigated the impact of SHANK3 disruption across multiple levels, from gene expression in patient-derived iPSC neurons to in vivo brain network activity. RNA-sequencing of iPSC-derived neurons from PMS patients with SHANK3 disruption only (n = 9) and controls (n = 7) revealed dysregulation in differential gene expression and co-expression modules linked to cell cycle, RNA metabolism, and metabolic pathways in SHANK3-mutated neurons. All modules were correlated with PMS regression and enriched for genes implicated in neurodevelopmental or neurodegenerative disorders, such as autism, ADHD, and Alzheimer's disease. At the cellular level, SHANK3-mutated cultures exhibited increased proliferation of neural progenitors and intermediate progenitor markers. Differentiated neurons showed reduced morphological complexity, specific changes in postsynaptic marker density and puncta size, and electrophysiological characteristics suggestive of neuronal hyperexcitability. Electroencephalography (EEG) in a PMS patient cohort (n = 20) compared to controls (n = 30) demonstrated hyperconnectivity and excessive high-frequency oscillations, suggesting altered neural network dynamics. In summary, the use of different analytical approaches suggested that SHANK3 haploinsufficiency disrupts neurodevelopmental trajectories and revealed that regression in PMS may share common genes and pathways with neurodegeneration. We also characterized molecular and neurophysiological markers that can be useful in therapeutic protocols for PMS.