Growth hormone is produced by the anterior pituitary gland. It has a role in the regulation of protein, lipid and carbohydrate metabolism, as well as in increasing growth in children. Its secretion is intermittent and occurs predominantly during deep sleep. Secretion reaches maximal levels during adolescence, and then declines with age by approximately 14% per decade.
Adult GH deficiency may be of adult onset or childhood onset, and may occur as isolated GH deficiency or as part of multiple pituitary hormone deficiency. In adult onset, GH deficiency is commonly due to pituitary tumours or their treatment, and to cranial irradiation. Childhood-onset GH deficiency is often idiopathic, and may continue into adulthood. Also, iatrogenic GH deficiency may occur in childhood or adulthood in survivors of childhood malignancy, as a result of previous cranial irradiation and/or chemotherapy.
The Society for Endocrinology estimates that the prevalence of adult-onset GH deficiency is approximately 1 in 10,000 of the adult UK population. If adults with childhood-onset GH deficiency are also considered, the prevalence may be as high approximately 12,600 adults with GH deficiency in England and Wales.
GH deficiency in adults may be associated with the following adverse features to a variable degree in any individual: reduced quality of life (QoL) especially reduced energy levels; altered body composition (reduced lean mass and increased fat mass, especially in the trunk); osteopenia/osteoporosis (reduced bone mineral density); dry skin (reduced sweating); reduced muscle strength and exercise capacity; lipid abnormalities (especially elevated LDL cholesterol); insulin resistance; increased levels of fibrinogen and plasminogen activator inhibitor; reduced extracellular fluid volume; increased thickness of the intima media of blood vessels; and impaired cardiac function.
Several tests are available for the diagnosis of GH deficiency. The ITT is regarded as the 'gold standard' test for adults. A general definition of severe GH deficiency in adults is a peak concentration of less than 9 mU/litre (3 ng/ml) in response to insulin-induced hypoglycaemia. When the ITT is contraindicated other tests – such as response to GH-releasing hormone, arginine or glucagon – can be used.
The clinical management of GH deficiency in adults is centred on replacement therapy with biosynthetic human GH (somatropin). However, there has been local variation in practice within the UK. The Society for Endocrinology estimates that approximately 1,750 adults with GH deficiency currently receive treatment in the UK.