Trisomy 21 Perturbs Oligodendrocyte Developmental States and Oligo-Neuron Communication in Human Forebrain Assembloids

Trisomic human forebrain assembloids show an expansion of BCAS1+ pre-myelinating oligodendrocyte lineage cells without increased MBP expression, indicating uncoupled differentiation from myelination.

• Why it matters: Down syndrome features abnormal connectivity and impaired myelination, but the developmental and neuron-glia mechanisms linking these phenotypes remain unclear.
• What they did: Using DS-derived isogenic induced pluripotent stem cell forebrain assembloids, the study compared euploid versus trisomic cultures with transcriptomics and ultrastructural analysis of neuron–glia contacts.
• The result: Trisomy-enriched OLLC_3-SID synaptic interaction programs and increased excitatory contacts with pre-myelinating OLLCs coincided with ultrastructural myelin abnormalities, suggesting trisomy redirects OLLC development toward a pre-myelinating state.

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