OR34-04 Defective FGFR1 Signaling Disrupts Glucose Regulation In Humans: Evidence From Patients With Isolated Hypogonadotropic Hypogonadism Harboring FGFR1 Mutations
Authors: Stamou Maria , Chiu Crystal Jane , Jadhav Shreya , Salnikov Kathryn , Plummer Lacey , Seminara Stephanie Beth , Balasubramanian Ravikumar 
Published: October 2023

Abstract
Disclosure: M. Stamou: None. C.J. Chiu: None. S. Jadhav: None. K. Salnikov: None. L. Plummer: None. S.B. Seminara: None. R. Balasubramanian: None.
Introduction: Recent studies have shown that antibody-mediated activation of FGFR1 receptor improves metabolic health in rodents, nonhuman primates, and humans. Hence, disruption of the FGFR1 receptor may lead to glucose dysregulation. FGFR1 mutations contribute to 12% of the genetic background of subjects with isolated hypogonadotropic hypogonadism (IHH), a rare Mendelian disease caused by GnRH deficiency. In this study, we examined glucose effectiveness and insulin sensitivity in IHH subjects with rare FGFR1 variants and hypothesized that these subjects will display defective glucose metabolism compared healthy non-carrier controls. Methods: Nine subjects with IHH (7 males and 2 females) with heterozygous rare FGFR1 variants were enrolled [7 subjects with protein truncating variants: p.Q680*, p.R622*, p.Q52*, p.I347Nfs*61, p.R576Pfs*77, p.Q309*, c.1553-2A&gt;G and 2 subjects with deleterious missense variants: p.G97S & p.Y701C. Thirty healthy controls (17 males and 13 females) with no FGFR1 variants were enrolled from the Mass General Brigham Biobank. Medical history, physical exam, laboratory evaluation, a bone density scan, and an intravenous glucose tolerance test (IVGTT) were performed. The area under the curve (AUC) for glucose, insulin, and C-peptide response to 50% dextrose (0.3g/kg, t=0min) and an insulin bolus (0.03u/kg, t=20 min) were estimated for each subject. The glucose effectiveness (Sg), insulin sensitivity (SI), acute insulin response to glucose (AIR), and the disposition index (DI= AIRG*SI) were calculated using the Minimal Model Analysis. Statistical comparisons were performed with t-test and non-parametric Wilcoxon rank sum test. A linear regression model was used to adjust the t-test outcomes for potential confounders. Results: Despite similar BMIs (28 vs. 26.5, p=0.29), IHH FGFR1 positive subjects demonstrated higher % fat mass compared to controls (38 vs. 31, p=0.02). IHH patients were supplemented with sex-steroids at the time of the study. Male patients demonstrated similar testosterone levels compared to controls (385 vs. 451 ng/dL, p=0.52). IHH FGFR1 positive subjects demonstrated a higher AUC for C-peptide compared to controls (167 vs. 92, p=0.001), that remained significant after adjusting for age, gender, BMI, and % fat mass. Non-parametric test showed higher AUC for glucose, insulin, and C-peptide (p 0.01, 0.01 & 0.005 respectively) as well as lower SI (p=0.01) and higher AIRg (p=0.037) in the IHH FGFR1 positive group compared to non-carrier controls. Discussion: This is the first study to evaluate glucose metabolism in humans with naturally occurring FGFR1 variants. IHH FGFR1 positive subjects showed higher insulin response to glucose and lower insulin sensitivity during an IVGTT test compared to the healthy non-carrier controls. These findings confirm that FGFR1 signaling is a key regulator of insulin secretion and action in humans.
Presentation: Sunday, June 18, 2023