Multiple sulfatase deficiency (MSD) is an ultra-rare, lysosomal storage disorder (LSD) characterized by the functional deficiency of all cellular sulfatases. MSD is caused by pathogenic variants in the gene SUMF1, encoding the sulfatase modifying factor formylglycine- generating enzyme (FGE). Variant forms of FGE are unable to sufficiently activate lysosomal sulfatases. Patients exhibit multisystemic clinical presentations characteristic of LSDs, but profound neurologic manifestations are always present. Given the rarity of MSD, the pathological mechanisms of disease are critically understudied and therapies for patients have not been thoroughly developed. Here, we investigated neuropathology in MSD as well as developed gene therapy to treat disease phenotypes. We first generated a novel patient-derived induced pluripotent stem cell (iPSC) model of MSD. We then differentiated these iPSCs into neural progenitor cells and neurogenin-2-induced neurons to elucidate mechanisms of neuropathology. The novel neural models of MSD recapitulated disease phenotypes including SUMF1 gene expression, lysosomal stress, neurite outgrowth and maturation, sulfatase activities, and storage accumulation. Using these models, we demonstrated that neurons exhibit a selective vulnerability compared to other cell types, suggesting the increased sensitivity of the central nervous system to disease pathology and mirroring patient phenotypes. We next developed a therapeutic approach to address the neurologic symptoms in MSD patients. We combined hematopoietic stem cell transplant with ex vivo gene therapy (HSCT-GT) and assessed its ability to correct disease in a clinically-relevant mouse model of MSD. We showed that SUMF1 HSCT-GT was able to rescue biochemistry and behavior in the MSD mouse, as measured by improvement in sulfatase activities, glycosaminoglycan accumulation, neuroinflammation, and neurocognitive behavior. To further augment outcomes, we evaluated the potential of ARSA HSCT-GT, encoding the downstream arylsulfatase A (ARSA), and dual SUMF1 and ARSA HSCT-GT to treat MSD mice. We found that co-expressing SUMF1 and ARSA enhanced biochemical rescue in MSD cells, serving as proof-of-concept to aid in the advancement of HSCT-GT for MSD. In summary, this dissertation establishes novel tools for the study of MSD pathology and lays the groundwork for the development of gene therapy for MSD.