Effects of Growth Hormone (GH) Deficiency and Growth Hormone Replacement on Serum Fibroblast Growth Factor 21 (FGF21)

Overview

This study will recruit healthy controls (who have normal GH production and growth hormone levels) and patients identified as having GHD, who are deemed eligible for GH replacement therapy according to NICE guidelines. The patients recruited will have been identified as starting on GH by their referring clinicians and a decision made on their replacement therapy prior to their potential enrollment in the study. The study, or its research team, will have no influence on the decision as to whether a patient will start on GH, or on which of the many GH formulations that the patients receives. The proposed study is an observational study to determine how GH affects the plasma levels of Fibroblast growth factor 21 (FGF21) in response to treatment; and whether the change in FGF21 mirrors the improvement in body composition/fat deposition. FGF21 is a metabolic regulator that acts on multiple tissues to coordinate carbohydrate and lipid metabolism and regulate energy balance. We hypothesize that FGF-21 is expressed and secreted from liver and skeletal muscle in humans in response to growth hormone administration and that levels may be reduced in patients with GHD compared with healthy controls. Furthermore, we believe that the beneficial effects of long-term GH replacement on body composition (reduction in visceral adipose tissue, subcutaneous adipose tissue and liver fat), on improvement in lipid profiles and on skeletal muscle mitochondrial function involve GH-induced release of FGF21.

Growth hormone (GH) is involved in controlling people's general health and an underproduction of growth hormone (growth hormone deficiency or GHD) leads to people feeling generally unwell and having a lower feeling of well-being and quality of life scores. In addition, the investigators, and others, have demonstrated people with GHD have reduced muscle and bone strength and a greater storage of fat, particularly in unfavourable sites such as in the liver and within the abdomen (visceral fat), rather than beneath the skin (subcutaneous fat). Treatment of GHD is achieved by administration of GH replacement therapy, given as a once daily subcutaneous injection, which generally reverses these symptoms. Due to its high cost, patients are only started on GH replacement depending on the impact that the GHD is having on their quality of life. Patients must be severely affected to be eligible for replacement therapy. Patients are screened for quality of life using a well validated, disease specific questionnaire (AGHDA, Adult Growth hormone deficiency questionnaire) and there are specific criteria that govern whether a patient with GHD warrants GH replacement and also whether they continue treatment (NICE guideline: Growth hormone deficiency (adults) - human growth hormone (TA64)). This study will specifically determine whether the mechanism of action by which GH exerts its beneficial effects on metabolism (within adipose tissue and skeletal muscle) involves changes in serum FGF21 concentrations.