Multiple sulfatase deficiency (MSD) is a rare lysosomal storage disorder caused by pathogenic variants in the sulfatase modifying factor 1 gene (SUMF1). Researchers from the University of Pennsylvania described the efficacy of hematopoietic stem cell transplantation (HSCT) with ex vivo SUMF1 lentiviral gene therapy (SUMF1-GT) in a mouse model of MSD.