FXYD1 (phospholemman) is a single-transmembrane protein regulator of the sodium/potassium-transporting ATPase (Na,K-ATPase), with abundant expression in heart, skeletal muscle, and kidney. In its unphosphorylated state, FXYD1 inhibits Na,K-ATPase activity by reducing the maximum velocity and raising the sodium affinity constant; phosphorylation at Ser-63 (by protein kinase C) or Ser-68 (by protein kinase A) reverses this inhibition and stimulates enzyme activity 1. FXYD1 also reduces glutathionylation-mediated inhibition of the Na,K-ATPase beta-1 subunit, further modulating ion homeostasis. Beyond electrolyte transport, FXYD1 contributes to female reproductive function by maintaining the excitability of neurons that secrete gonadotropin-releasing hormone. FXYD1 dysregulation appears in multiple clinical contexts: abnormal expression occurs in Hirschsprung's disease 2, recurrent miscarriage involves increased FXYD1 expression that impairs decidualization 3, and upregulation of FXYD1 in astrocytes is associated with elevated extracellular potassium and neuronal loss in Alzheimer's disease and amyotrophic lateral sclerosis 4. In recurrent miscarriage patients, Na,K-ATPase inhibition offers a potential therapeutic avenue 3. These findings position FXYD1 as a key regulator linking ion transport dysfunction to cardiac, muscular, and neurological disease pathology.