Focusing on the tetra-partite synapse in Parkinson's disease research using human patient-derived neurons

Case Report: A Case of a Patient with Smith-Magenis Syndrome and Early-Onset Parkinson's Disease

Smith-Magenis Syndrome (SMS) is a rare genetic disorder, characterized by intellectual disability (ID), behavioral impairments, and sleep disturbances, as well as multiple organ anomalies in some affected individuals. The syndrome is caused by a deletion in the chromosome band around 17p11.2, including the Retinoic Acid Induced 1 (RAI1) gene, a multifaceted transcriptional regulator that modulates the expression of genes involved in cellular proliferation and neurodevelopment. This gene has a positive role in regulating BDNF and, importantly, affects several cell mechanisms and pathways such as the nigro-striatal pathway, which is crucial for motor function. Parkinson's disease (PD) is one of the most common neurodegenerative diseases in older populations. It is characterized by various physical symptoms including tremors, loss of balance, bradykinesia, and a stooping posture. We present a case study of a patient diagnosed with both SMS and early-onset PD (at the age of 49). The association between both conditions is as yet ambiguous. Genome-wide association studies (GWAS) implicate an association between the RAI1 gene and PD. Similarly, the co-existence of both SMS and PD in the patient suggests a possible association between RAI1 copy number variations (CNVs) and PD, further indicating that RAI1 has strong implications for PD pathogenesis. Our results suggest that RAI1 CNVs and the pathophysiology of PD may be related, underscoring the need for further research in this field. Therefore, caregivers of SMS patients should pay careful attention to the possibility of their patients developing EOPD and should consider starting treatment for PD as soon as the first symptoms appear.

Synaptic dysfunction and extracellular matrix dysregulation in dopaminergic neurons from sporadic and E326K-GBA1 Parkinson's disease patients

Parkinson's disease (PD) is a neurodegenerative disease with both genetic and sporadic origins. In this study, we investigated the electrophysiological properties, synaptic activity, and gene expression differences in dopaminergic (DA) neurons derived from induced pluripotent stem cells (iPSCs) of healthy controls, sporadic PD (sPD) patients, and PD patients with E326K-GBA1 mutations. Our results demonstrate reduced sodium currents and synaptic activity in DA neurons derived from PD patients with E326K-GBA1 mutations, suggesting a potential contribution to PD pathophysiology. We also observed distinct electrophysiological alterations in sPD DA neurons, which included a decrease in synaptic currents. RNA sequencing analysis revealed unique dysregulated pathways in sPD neurons and E326K-GBA1 neurons, further supporting the notion that molecular mechanisms driving PD may differ between PD patients. In agreement with our previous reports, Extracellular matrix and Focal adhesion pathways were among the top dysregulated pathways in DA neurons from sPD patients and from patients with E326K-GBA1 mutations. Overall, our study further confirms that impaired synaptic activity is a convergent functional phenotype in DA neurons derived from PD patients across multiple genetic mutations as well as sPD. At the transcriptome level, we find that the brain extracellular matrix is highly involved in PD pathology across multiple PD-associated mutations as well as sPD.