Insensitivity to GH is traditionally termed Laron dwarfism, but over the last 15 years many different types of GH resistance have been identified, primarily involving mutations of the GH binding protein or receptors.Familial isolated growth hormone deficiency (IGHD) can be inherited as an autosomal recessive (type I), autosomal dominant (type II), or X-linked (type III) characteristic. Pathophysiology
As an adult ages, it is normal for the pituitary to produce diminishing amounts of GH and many other hormones, particularly the sex steroids. Physicians, therefore, distinguish between the natural reduction in GH levels which comes with age, and the much lower levels of "true" deficiency. Such deficiency almost always has an identifiable cause, with adult-onset GHD without a definable cause ("idiopathic GH deficiency") extremely rare. GH does function in adulthood to maintain muscle and bone mass and strength, and has poorly understood effects on cognition and mood. Diagnosis
Although GH can be readily measured in a blood sample, testing for GH deficiency is constrained by the fact that levels are nearly undetectable for most of the day. This makes simple measurement of GH in a single blood sample useless for detecting deficiency.
: 501

Adults
Recognised effects include:
Increased 5-alpha-reductase
Reduced sex hormone-binding globulin (SHBG)
Reduced muscle mass and strength
Baldness in men
Reduced bone mass and osteoporosis (Decreased bone density)
Reduced energy
Impaired concentration and memory loss
Increased body fat, particularly around the waistline
Lipid abnormalities, particularly raised LDL cholesterol
Increased levels of fibrinogen and plasminogen activator inhibitor
Cardiac dysfunction, including a thickened intima media
Lack of well-being
Depression and anxiety
Social isolation
Fibromyalgia syndrome
Neuromuscular dysfunction
Central adiposity
Decreased muscle mass
Insulin resistance
Accelerated atherogenesis
Prothrombotic state
Decreased sweating and thermoregulation. Causes
Growth hormone deficiency in childhood commonly has no identifiable cause (idiopathic), and adult-onset GHD is commonly due to pituitary tumours and their treatment or to cranial irradiation. A more complete list of causes includes:

mutations of specific genes (e.g., GHRHR, GH1)
congenital diseases such as Prader-Willi syndrome, Turner syndrome, or short-stature homeobox gene deficiency
congenital malformations involving the pituitary (e.g., septo-optic dysplasia, posterior pituitary ectopia)
chronic kidney disease
intracranial tumors in or near the sella turcica, especially craniopharyngioma
damage to the pituitary from radiation therapy to the head (e.g. for leukemia or brain tumors), from surgery, from trauma, or from intracranial disease (e.g. hydrocephalus)
autoimmune inflammation (hypophysitis)
ischemic or hemorrhagic infarction from low blood pressure (Sheehan syndrome) or hemorrhage pituitary apoplexyThere are a variety of rare diseases that resemble GH deficiency, including the childhood growth failure, facial appearance, delayed bone age, and low insulin-like growth factor-1 (IGF-1) levels. However, GH testing elicits normal or high levels of GH in the blood, demonstrating that the problem is not due to a deficiency of GH but rather to a reduced sensitivity to its action.