MECP2 and Rett syndrome: Poor growth is common in Rett syndrome.7 The MECP2 mutation likely has a role, but other contributing factors include poor muscle tone and oromotor incoordination, which can cause feeding difficulties.8 Gastrointestinal dysmotility may lead to gastroesophageal reflux disorder, delayed gastric emptying, and/or constipation.9 Many have disturbed breathing patterns with episodic hyperventilation, breath holding, aerophagia, and abdominal distension causing discomfort and reduced oral intake.