Objective: To characterize transcriptomic alterations in patient-derived midbrain organoids carrying NOTCH2NLC GGC repeat expansions and assess their relevance to canonical Parkinson’s disease (PD) mechanisms.

Background: GGC repeat expansions in the 5’UTR of NOTCH2NLC cause NIID, which shows broad phenotypic heterogeneity, including parkinsonism in some patients. While dopaminergic neuron loss and α-synuclein aggregation are cardinal features of PD, the molecular link between NOTCH2NLC-related parkinsonism and classical PD pathways remains unclear. Induced pluripotent stem cell (iPSC)-derived midbrain organoids provide a model of early PD pathogenesis.

Method: Skin fibroblasts from three patients with NOTCH2NLC GGC repeat expansion-associated PD and three healthy controls were reprogrammed into iPSCs and differentiated into midbrain organoids. Dopaminergic neuronal identity was confirmed by immunofluorescence. Day-90 organoids underwent bulk and single-cell RNA sequencing. Differential expression, gene ontology (GO) enrichment, and gene set enrichment analyses (GSEA) were performed.

Results: Patient-derived organoids generated A9-subtype dopaminergic neurons positive for TH, DAT, and GIRK2. Bulk RNA sequencing revealed transcriptional remodeling, with upregulated genes enriched in neurogenesis, synaptic structure, and neuronal signaling, whereas downregulated genes converged on cell cycle regulation. GSEA showed positive enrichment of synapse-related pathways and negative enrichment of ribosomal and translational gene sets. Single-cell RNA sequencing identified a reduced proportion of radial glia-like cells and an expanded GABAergic neuronal population. Within the dopaminergic neuron cluster, upregulated genes were enriched in postsynaptic density and small GTPase signaling, whereas downregulated genes were concentrated in nucleotide metabolism and ATP biosynthesis, particularly mitochondrial respiratory chain subunits.

Conclusion: NOTCH2NLC GGC repeat expansion-associated PD exhibits molecular abnormalities including aberrant developmental transcriptional activation, synaptic remodeling, translational suppression, and dopaminergic neuron-specific mitochondrial bioenergetic impairment. These findings link NOTCH2NLC repeat expansions to canonical PD mechanisms.

« Back to 2026 International Congress

MDS Abstracts - https://www.mdsabstracts.org/abstract/midbrain-organoid-modeling-and-transcriptomic-characterization-of-notch2nlc-ggc-repeat-expansion-associated-parkinsons-disease/