The Increased FCRL mRNA Expression in Patients with Graves’ Disease Is Associated with Hyperthyroidism (But Not with Positive Thyroid Antibodies)

<b>Background:</b> Fc receptor-like (FCRL) genes play a role in the immune system by encoding proteins that function as receptors on the surface of immune cells. The clinical significance of FCRL gene expression in Graves' Disease (GD) and Graves' Orbitopathy (GO) remains unclear. We evaluated the expression of FCRL 2, 3, 4 mRNA in patients with GD and GO and its role in the development and activity of these diseases. <b>Methods:</b> Peripheral blood samples from patients with GD (<i>n</i> = 24) or GO (<i>n</i> = 49) hospitalized in the Department of Endocrinology and Metabolic Diseases, Medical University of Lodz, were collected. Expressions of FCRL2, FCRL3 and FCRL4 were measured by real-time PCR. <b>Results</b>: FCRL3 expression was higher in patients with GD compared to GO (1.375 vs. 0.673, <i>p</i> = 0.004) and, specifically, active GO (1.375 vs. 0.639, <i>p</i> = 0.005). Regarding FCRL4, mRNA expression was higher in GD compared to Control (3.078 vs. 0.916, <i>p</i> = 0.003), GO (3.078 vs. 1.178, <i>p</i> < 0.001), active GO (3.078 vs. 1.186, <i>p</i> = 0.002) and inactive GO (3.078 vs. 1.171, <i>p</i> = 0.008). In turn, FCRL4 mRNA expression was higher in patients with hyperthyroidism (subclinical + overt) than in euthyroid patients (2.509 vs. 0.995, <i>p</i> = 0.001 when the whole group of individuals was considered; 2.509 vs. 1.073, <i>p</i> = 0.004 when GO + GD was considered). <b>Conclusions:</b> The increased FCRL mRNA expression in patients with GD is associated with hyperthyroidism (but not with positive TSHRAbs), and our study is the first one to confirm this relationship.