Complex sentence: Ondine's curse, is most commonly used to refer to congenital central hypoventilation syndrome (CCHS) or primary alveolar hypoventilation, is a respiratory disorder that is fatal if untreated.
Split into simpler sentences: Ondine's curse, is most commonly used to refer to congenital central hypoventilation syndrome (CCHS) or primary alveolar hypoventilation. CCHS is a respiratory disorder that is fatal if untreated.