What is situs inversus? The incredibly rare illness Catherine O’Hara was diagnosed with

Beloved actress Catherine O’Hara, whose decades-long career included unforgettable turns in Home Alone, Beetlejuice and Schitt’s Creek, had been living with a rare genetic condition called situs inversus, she revealed years before her death at age 71.

Macaulay Culkin has shared a tribute (Picture: Century Fox/Kobal/Shutterstock)

Situs inversus is a congenital anomaly in which a person’s internal organs are arranged as a mirror image of the typical configuration — meaning her heart was on the right side of her chest, and other organs such as the liver and spleen were reversed as well. It’s an exceptionally rare condition, affecting roughly one in every 10,000 people, and most sufferers have no symptoms or health problems because of it.

O’Hara first learned about her diagnosis more than two decades ago during a routine doctor visit that included an electrocardiogram and chest X-ray. She recounted that the moment became a bit of family lore, with her husband joking that “her head’s on backwards” when the doctor shared the unexpected news. She even joked about her “backwards” organs in public appearances, using humor to embrace the quirks that made her unique.

Catherine shared her diagnosis in 2021 (Picture: Axelle/Bauer-Griffin/FilmMagic)

Although situs inversus on its own usually doesn’t cause major health issues, it can sometimes make medical diagnoses more complicated because symptoms may present on the opposite side of the body from where physicians typically expect them.

At the time of her passing on January 30, 2026, O’Hara had been hospitalized following what her representatives described as a “brief illness.” An official cause of death has not been confirmed, and there is no indication that situs inversus played any direct role in her final illness.

Fans around the world remember O’Hara not for her rare medical condition but for her warmth, wit and career that brought laughter to generations.