Deletion of the PREPL (prolyl endopeptidase-like) gene was detected in patients with congenital myastemic syndrome 22 (CMS22) [45,46,47], and, together with the neighboring SLC3A1 gene, the PREPL gene is deleted in patients with hypotonia–cystinuria syndrome (HCS) [41,48,49]. The gene discussed is PREPL; the disease is Hypotonia.