Astrocytes differentiated from patient iPSCs model the rare leukodystrophy MLC and uncover disease-linked maturation defects and Kir4.1 channel dysfunction.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare leukodystrophy caused by astrocyte dysfunction. Mutations in the MLC1 gene, which encodes the astrocyte-specific membrane protein MLC1 represent the main cause. MLC is characterized by myelin vacuolation, subcortical cysts, and brain edema. Clinically, patients show motor impairments such as ataxia and spasticity, and epilepsy. Currently, the function of MLC1 and the molecular mechanisms underlying MLC remain poorly understood, limiting therapeutic development. This is especially relevant since symptom reversibility has been observed in some patients. To date, functional studies have mainly relied on mouse models, which do not fully reproduce human pathology. To develop a more relevant disease model, we generated astrocytes from induced pluripotent stem cells (iPSCs) derived from fibroblasts of three healthy donors and three MLC patients. Using molecular, biochemical, electrophysiological, and imaging approaches, we found that MLC astrocytes show impaired volume regulation, cytoplasmic vacuolation, and altered EGF receptor expression, consistent with prior MLC models. Notably, we also revealed endosomal alterations, increased proliferation, and abnormal expression of the critical astrocyte maturation markers EAAT1, GFAP, Cx43, AQP4, and Kir4.1, the latter causing impaired potassium currents in patient-derived cells. These results provide the first evidence that MLC1 mutations alter astrocyte maturation and potassium homeostasis, potentially contributing to disease pathogenesis. Our patient-specific iPSC-derived model offers novel insights into the molecular basis of MLC and highlights the role of MLC1 in astrocyte development. This platform represents a valuable tool for preclinical drug screening and supports the development of personalized therapeutic strategies for this rare leukodystrophy.