Daybue is the first drug approved to treat the rare neurodevelopmental disorder Rett syndrome, despite high clinical trial incidence of diarrhea. Product labeling includes clinician guidance for the side effect.

Ultragenyx is buying its Angelman syndrome partner GeneTx for $75m on the heels of an interim Phase I/II readout that shows signs of clinical activity and appears to resolve earlier safety worries.

Trofinetide could be the first approved drug for Rett patients after hitting both co-primary endpoints in a Phase III trial, but high rates of diarrhea and vomiting raise questions.