ATP6AP1 and immunodeficiency disease: Fourteen patients have been reported with the X‐linked ATP6AP1 deficiency (ATP6AP1‐CDG).1, 2, 3 Key features were immunodeficiency and liver involvement.1 Some patients also showed neurological involvement, connective tissue involvement, glomerular and tubular dysfunction, sensorineural hearing loss, exocrine pancreatic insufficiency and/or altered amino acid and lipid metabolism.2, 3