SLC18A3 and ptosis: Muscle hypotonus, palpebral ptosis, and sleep apnea in these patients may be caused by haploinsufficiency of CHAT and SLC18A3. However, as stated above, as hemiallelic null variants are symptomatic in parents of CHAT-CMS, either complete lack of vAChT (SLC18A3) that is intact in CHAT-CMS or an unidentified pathogenic variant on the other allele may cause the disease.