MSMDS Awareness Day is observed worldwide every June 10 to promote understanding of multisystemic smooth muscle dysfunction syndrome (MSMDS), a rare genetic disorder caused by mutations in the ACTA2 gene. This day was established by the ACTA2 Alliance, a nonprofit organization dedicated to raising awareness of MSMDS and related conditions. MSMDS is characterized by its impact on various organs, including the bladder, esophagus, lungs, and stomach, and is marked by key signs such as aortopulmonary window, congenital mydriasis, and white matter changes in the brain. There are fewer than 50 known cases globally, and while there is no cure, treatment focuses on managing symptoms and improving quality of life through a multidisciplinary approach. Activities on this day include educating others about MSMDS, fundraising for the ACTA2 Alliance, and sharing information on social media using the hashtag #MSMDSAwarenessDay.