Pathogenic variants in CHRNE encoding the epsilon subunit of acetyl choline receptor (AChR) result in impaired neuromuscular transmission and congenital myasthenic syndromes (CMS). Clinical manifestations include facial, ocular and limb fatigability and weakness, whereby severity of symptoms may vary in patients harboring the same pathogenic variant. Although the underlying pathophysiology is well-known, blood biomarkers enabling a patient-stratification are lacking. Previous studies revealed CHRNE protein in white blood cells (WBC) rendering these cells suitable for the study of cellular and minimal-invasive marker proteins.