MSD World Day is observed worldwide every July 30 to highlight multiple sulfatase deficiency (MSD), a rare genetic disorder classified as a lysosomal storage disease. The day was established by a coalition of MSD foundations from Argentina, Ireland, Spain, and the United States, and features various events and activities aimed at supporting families affected by MSD and funding research. Activities include fundraisers, social media campaigns, and the illumination of buildings and landmarks. MSD is caused by a mutation in the SUMF11 gene, leading to the accumulation of harmful substances in cells and resulting in severe symptoms that typically manifest between one and two years of age. There is currently no cure for MSD, and management requires a multidisciplinary approach involving various specialists.