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Parkinson’s disease (PD) caused by <i>SNCA</i> gene triplication (3X<i>SNCA</i>) leads to early onset, rapid progression, and often dementia. Understanding the impact of 3X<i>SNCA</i> and its absence is crucial. This study investigates the differentiation of human induced pluripotent stem cell (hiPSC)-derived floor-plate progenitors into dopaminergic neurons. Three different genotypes were evaluated in this study: patient-derived hiPSCs with 3X<i>SNCA</i>, a gene-edited isogenic line with a frame-shift mutation on all <i>SNCA</i> alleles (<i>SNCA</i> 4KO), and a normal wild-type control. Our aim was to assess how the substantia nigra pars compacta (SNpc) microenvironment, damaged by 6-hydroxydopamine (6-OHDA), influences tyrosine hydroxylase-positive (Th+) neuron differentiation in these genetic variations. This study confirms successful in vitro differentiation into neuronal lineage in all cell lines. However, the <i>SNCA</i> 4KO line showed unusual LIM homeobox transcription factor 1 alpha (Lmx1a) extranuclear distribution. Crucially, both 3X<i>SNCA</i> and <i>SNCA</i> 4KO lines had reduced Th+ neuron expression, despite initial successful neuronal differentiation after two months post-transplantation. This indicates that while the SNpc environment supports early neuronal survival, <i>SNCA</i> gene alterations—either amplification or knock-out—negatively impact Th+ dopaminergic neuron maturation. These findings highlight <i>SNCA</i>’s critical role in PD and underscore the value of hiPSC models in studying neurodegenerative diseases.