Growth hormone deficiency (GHD), or hyposomatotropism, is a medical condition resulting from not enough growth hormone (GH). Generally the most noticeable symptom is that an individual attains a short height. Newborns may also present low blood sugar or a small penis size. In adults there may be decreased muscle mass, high cholesterol levels, or poor bone density. GHD can be present at birth or develop later in life. Causes may include genetics, trauma, infections, tumors, or radiation therapy. Genes that may be involved include GH1, GHRHR, or BTK. In a third of cases no cause is apparent. The underlying mechanism generally involves problems with the pituitary gland. Some cases are associated with a lack of other pituitary hormones, in which case it is known as combined pituitary hormone deficiency. Diagnosis involves blood tests to measure growth hormone levels. Treatment is by growth hormone replacement using synthetic human growth hormone. The frequency of the condition is unclear. Most cases are initially noticed in children. The genetic forms of this disease are estimated to affect about 1 in 7,000 people. Most types occur equally in males and females though males are more often diagnosed.
Signs and symptoms
Child Severe prenatal deficiency of GH, as occurs in congenital hypopituitarism, has little effect on fetal growth. However, prenatal and congenital deficiency can reduce the size of a male's penis, especially when gonadotropins are also deficient. Besides micropenis in males, additional consequences of severe deficiency in the first days of life can include hypoglycemia and exaggerated jaundice (both direct and indirect hyperbilirubinemia). Even congenital GH deficiency does not usually impair length growth until after the first few months of life. From late in the first year until mid-teens, poor growth and/or shortness is the hallmark of childhood GH deficiency. Growth is not as severely affected in GH deficiency as in untreated hypothyroidism, but growth at about half the usual velocity for age is typical. It tends to be accompanied by delayed physical maturation so that bone maturation and puberty may be several years delayed. When severe GH deficiency is present from birth and never treated, adult heights can be as short as 48–65 inches (120–170 cm). Severe GH deficiency in early childhood also results in slower muscular development, so that gross motor milestones such as standing, walking, and jumping may be delayed. Body composition (i.e., the relative amounts of bone, muscle, and fat) is affected in many children with severe deficiency, so that mild to moderate chubbiness is common (though GH deficiency alone rarely causes severe obesity). Some severely GH-deficient children have recognizable, cherubic facial features characterized by maxillary hypoplasia and forehead prominence. Other side effects in children include sparse hair growth and frontal recession, and pili torti and trichorrhexis nodosa are also sometimes present.
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 apoplexy There 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. 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. Physicians, therefore use a combination of indirect and direct criteria in assessing GHD, including:
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