List of causes of Ondine's curse. Following is a list of causes or underlying conditions (see also Misdiagnosis of underlying causes of Ondine's curse) that could possibly cause Ondine's curse includes: Persons who have CCHS get it at birth, or develop it due to severe neurological trauma/damage to the brainstem.
In real life, Della (Barbara Hale) was married and Perry (Raymond Burr) was gay. So, no, they were not an item on the show or behind the scenes.
Barbara Hale returned as Della Street, probably the most popular character of the series after Perry himself. Unfortunately, all of the other cast members listed above had already passed on: William Hopper in 1970, William Talman in 1968, and Ray Collins in 1965, before the original series even ended.