As Amber Olsen, the key subject of the documentary and the titular “Bear,” states, there are thousands of rare diseases that receive no support from healthcare systems in the US or around the world, essentially meaning that thousands, if not millions, of people watch their loved ones suffer without any hope for improvement. Her daughter, Willow, the “Zebra” of the title, was diagnosed with the ultra-rare and fatal condition Multiple Sulfatase Deficiency (Msd) when she was two years old, setting off a journey for her and her husband Tom that took them from devastation to defiance and determined action. Their struggle became the foundation for “The Zebra and the Bear.”

Patrick O’Connor documented the family over the course of more than seven years, beginning with what was originally a short fundraising video. What unfolded became a deeply immersive account of the Olsens’ pursuit of hope within a system ill-equipped to...