Background Congenital myasthenic syndrome with episodic apnoea (CMS-EA) is a rare but potentially treatable cause of apparent life-threatening events in infancy. The underlying mechanisms for sudden and recurrent episodes of respiratory arrest in these patients are unclear. Whilst CMS-EA is most commonly caused by mutations in CHAT , the list of associated genotypes is expanding. Methods We reviewed clinical information from 19 patients with CMS-EA, including patients with mutations in CHAT , SLC5A7 and RAPSN , and patients lacking a genetic diagnosis. Results Lack of genetic diagnosis was more common in CMS-EA than in CMS without EA (56% n  = 18, compared to 7% n  = 97). Most patients manifested intermittent apnoea in the first 4 months of life (74%, n  = 14). A degree of clinical improvement with medication was observed in most patients (74%, n  = 14), but the majority of cases also showed a tendency towards complete remission of apnoeic events with age (mean age of resolution 2 years 5 months). Signs of impaired neuromuscular transmission were detected on neurophysiology studies in 79% ( n  = 15) of cases, but in six cases, this was only apparent following specific neurophysiological testing protocols (prolonged high-frequency stimulation). Conclusions A relatively large proportion of CMS-EA remains genetically undiagnosed, which suggests the existence of novel causative CMS genes which remain uncharacterised. In light of the potential for recurrent life-threatening apnoeas in early life and the positive response to therapy, early diagnostic consideration of CMS-EA is critical, but without specific neurophysiology tests, it may go overlooked.