What is dwarfism?
Dwarfism in humans may be caused by a number of conditions that occur either before birth or in early childhood. When short stature is the only observable feature, growth—though abnormal relative to height—is proportionate. Short stature is nearly always attributed to endocrinological dysfunction, but few cases are actually the result of endocrinopathy. If short stature is caused by endocrinopathy, it is often attributable to a deficiency in the pituitary gland (which produces growth hormone) or the thyroid gland. Those who are unusually short but have no other obvious disease are divided into two categories: those who were afflicted prenatally and those who were afflicted postnatally. Many cases are actually the result of chromosomal or skeletal aberrations; other events that may inhibit prenatal growth include magnesium deficiency (which would prohibit ribosome synthesis and, in turn, halt protein synthesis) or a uterus that is too small. Postnatal inhibition of growth may be caused by heredity if both parents are short; there is no skeletal abnormality at fault. Other short-statured children may simply mature at a much slower rate, yet grow normally. Typically, one of the parents may have had a late onset of puberty.
Unusually short-statured males are those who are shorter than sixty inches tall; in females, fifty-eight inches and below is short-statured. Children are classified as dwarfs if their height is below the third percentile for their age. When this is the case, doctors will look primarily to four major causes of dwarfism: an underactive or inactive pituitary gland, achondroplasia (failure of normal development in cartilage), emotional or nutritional deprivation, or Turner syndrome (the possession of a single, X, chromosome). If the answer is not found in one of these alternatives, then it may be found in rarer causes, either genetically based or disease induced.
Growth hormone, also called somatotropin, determines a person’s height. Growth hormone does not affect brain growth but may influence the brain’s functions. In addition, it may enhance the growth of nerves radiating from the brain so that they can reach their targets. Growth hormone elevates the appetite, increases metabolic rate, maintains the immune system, and works in coordination with other hormones to regulate carbohydrate, protein, lipid, nucleic acid, water, and electrolyte metabolism. Target areas for growth hormone include cell membranes as well as other cell organelles in bone, cartilage, bone marrow, adipose tissue, and the liver, kidney, heart, pancreas, mammary glands, ovaries, testes, thymus gland, and hypothalamus. Fetuses not producing growth hormone still grow normally until birth; they may even weigh more than average at birth. These babies may thrive at first, but if no growth hormone is administered, they will grow to a maximum height of thirty inches. Other telltale physical attributes include higher-than-average body fat, a high forehead, wrinkled skin, and a high-pitched voice. During childhood, there may be episodic hypoglycemia attacks. If the endocrine system is functioning properly, puberty may be delayed but will still occur. Complete reproductive maturity will be reached, and there is great likelihood that the afflicted person will develop his or her complete intellectual potential. When it is inherited, growth hormone deficiency occurs as an autosomal recessive trait. Yet the genetic basis for growth hormone deficiency may not simply be caused by a gene. The condition could, in theory, be the result of a structural defect in the pituitary gland or the hypothalamus, or in the secretory mechanisms of growth hormone itself. Prenatal factors that contribute to the inhibition of growth include toxemia, kidney and heart disease, rubella, maternal malnutrition, maternal age, small uterus, and environmental influences such as alcohol and drug use.
Prenatal thyroid dysfunction that goes untreated results in congenital hypothyroidism . Children with this disorder do not undergo nervous, skeletal, or reproductive maturation; they may not grow over thirty inches tall. When administered before a child is two months of age, treatment can cause a complete reversal of symptoms. Delayed treatment, however, cannot reverse brain damage, although growth and reproductive organs can be dramatically affected.
Achondroplasia is the most common form of short-limb dwarfism. It is inherited as an autosomal dominant form of dwarfism. Achondroplasia is expressed only when one copy of the gene is present; when an offspring inherits the dominant gene from both parents, the condition is lethal. Incidence of achondroplasia increases with parental age and is more closely related to the father’s age. Mutations may account for a majority of cases of achondroplasia, since there is an affected parent in only about 20 percent of cases. Achondroplasia results from abnormal embryonic development that affects bone growth; metaphyseal development is prevented, which means that cartilaginous bone growth is impaired. This is accompanied by unusually small laminae of the spine, resulting in spinal stenosis. The spinal cord may become compressed during the normal process of spondylosis. Individuals with achondroplasia may experience slowly progressing weakness of the legs as a result of the spinal cord compression. Achondroplasia is often distinguished by the presence of a disproportionately large head and dwarfed and curved limbs; in addition, an individual may have a prominent forehead and a depressed nasal bridge. A shallow thoracic cage and pelvic tilt may cause a protuberant abdomen. Bowlegs are caused by overly long fibulae. Individuals with achondroplasia who live to adulthood are typically thirty-six to sixty inches tall and have unusual muscular strength; reproductive and mental development are not affected, and neither is longevity.
Marasmus, severe emaciation resulting from malnutrition prenatally or in early infancy, may be considered a form of dwarfism. It is caused by extremely low caloric and protein intake, which causes a wasting of body tissues. Usually marasmus is found in babies either weaned very early or never breast-fed. All growth is inhibited, including head circumference. If the area housing the brain fails to grow, then it cannot house a normal-sized brain, and the individual may develop an intellectual disability. Infants with marasmus are frequently apathetic and hyperirritable. As they lie in bed, they are completely unresponsive to their environment and are irritable when moved or handled. Although the symptoms are treatable and may disappear, the inhibition of growth is permanent.
Occasionally, dwarfism may be induced by emotional starvation. This type of child abuse causes extreme growth inhibition, inhibition of skeletal growth, and delayed psychomotor development. Fortunately, it can be reversed by social and dietary changes. Children with this form of dwarfism are extremely small but perfectly proportioned; however, they have distended abdomens.
The height achieved in females with Turner syndrome is typically between fifty-four and sixty inches. Turner syndrome results when an egg has no X chromosome and is fertilized by an X-bearing sperm. The offspring are females with only one X chromosome. These individuals cannot undergo puberty; their ovaries never develop and are unable to function. Physical manifestations of Turner syndrome include short stature, stocky build, and a webbed neck.
Another cause of short stature may be as a consequence of chronic disease. Children with chronic renal (kidney) failure nearly always experience inhibition of growth because of hormonal, metabolic, and nutritional abnormalities. This occurs more often in children with congenital renal disease than in those with acquired renal disease.
With congenital heart disease, several factors may prohibit growth. Growth inhibition may be a direct result of the disease or an indirect result of other problems associated with heart disease. These babies experience stress, with periods of cardiac failure, and either caloric or protein deficiency. These conditions slow the multiplication of cells and hence growth. If surgery corrects the condition, some catching up can be expected, depending on how much time has elapsed without treatment.
The more a child is below the average stature, the greater the likelihood of determining the cause. A child who is short statured should be evaluated so that if an endocrine disorder is the root, the child can be treated. Time is an important consideration with hypothyroidism especially, since the longer it goes untreated, the more likely it is that mental development will be arrested.
Children born with congenital growth hormone deficiency are sometimes small for their gestational age; however, the majority of children with growth hormone deficiency acquire the disorder after birth. For the first year or two, the children grow normally, but growth then dramatically decreases. Diagnosis of growth hormone deficiency requires numerous tests and sampling. If bone age appears the same as the child’s age, then growth hormone deficiency can be eliminated. A test for growth hormone secretion is performed by measuring a blood sample for growth hormone twenty minutes after exercise in a fasting child. If this test shows a hormone deficiency, then growth hormone therapy may allow the child to continue to grow.
At first, growth hormone was harvested from human pituitary glands after persons’ deaths. This process was so expensive, however, that few children with hormone deficiency could be treated. Even worse, some of those who did undergo this treatment were inadvertently infected with a slow-acting virus that proved fatal. In the mid-1980s, it was found that some men who had received human growth hormone died at an early age of a neurological disorder called Creutzfeldt-Jakob disease (CJD). These men were found to have contracted the disease via a growth hormone that had been obtained from pituitary glands during autopsies. Once the relationship was determined, more victims were identified. CJD is a nervous disorder caused by a slow-acting, viruslike particle. Its symptoms include difficulty in balance while walking, loss of muscular control, slurred speech, impairment of vision, and other muscular disorders. Behavioral and mental changes such as memory loss, confusion, and dementia may also occur. The symptoms appear, progress rapidly over the next months, and usually cause death in less than a year. There is no treatment or cure.
These unfortunate circumstances led to the development of a synthetic growth hormone. It is made by encoding bacterial deoxyribonucleic acid (DNA) with the sequence of human growth hormone; the bacteria used are those that grow normally in the human intestinal tract. The bacteria synthesize human growth hormone using the preprogrammed human sequence of DNA; it is then purified so that no bacteria remain in the hormone that is used for treatment. The Food and Drug Administration (FDA) approved the biosynthetic hormone in 1985. The sole difference between the synthetic and the naturally produced growth hormone was one amino acid; in 1987, a new synthetic form without the extra amino acid became available. This synthetic hormone works exactly as natural growth hormone does. Moreover, it does not carry the danger of contamination. In most cases, the patient’s immune system does not interfere with the synthetic growth hormone’s effectiveness.
Those children with various forms of chondrodystrophies (cartilage disorders), such as achondroplasia, are diagnosed using skeletal measurements, clinical manifestations, x-rays, laboratory study and analysis of cartilage, and observed abnormalities of the body’s proteins, such as collagen and cell membranes. In chondrodystrophies, skeletal growth is disproportionate, with shortened limbs more common than a shortened trunk. If visual examination is not confirmation enough, the diagnosis may be assured through x-rays. Although histological studies do not necessarily enhance diagnosis, making an analysis of the patient’s cartilage may lead to a better understanding of the condition. Biochemical studies of abnormal proteins in chondrodystrophies actually have little diagnostic value, but they too may lead to better understanding. Because achondroplasia is genetically inherited, prevention involves genetic counseling before conception.
A child with achondroplasia may be treated symptomatically; surgery on the fibulae to correct bowlegs may be desirable, either for cosmetic reasons or for functional reasons. Laminectomies or skull surgery may be indicated for neurological problems. Orthodontic surgery may be necessary to correct malocclusions and other dental deformities. If hearing loss occurs because of recurrent ear infections, then corrective surgery may be necessary. Individuals with achondroplasia generally enjoy a normal life span, barring complications.
Other chondrodystrophies that cause dwarfism may have more severe symptoms than achondroplasia. Cockayne syndrome, a type of progeria, is the sudden onset of premature old age in extremely young children. It is the result of inheritance of an autosomal recessive gene. Physical signs of the disease begin after a normal first year of life. In the second year, growth begins to falter, and psychomotor development becomes abnormal. As time passes, dwarfism becomes evident. Other observable characteristics that develop are a shrunken face with sunken eyes and a thin nose, optic degeneration, cavities of the teeth, a photosensitive skin rash that produces scarring, disproportionately long limbs with large hands and feet, and hair loss. The life span for children with this disease is very short.
Another chondrodystrophy inherited through autosomal recessive genes is thanotophoric dwarfism. All known individuals with this condition have died during the first four weeks of life as a result of respiratory distress; most are stillborn. Thanotophoric dwarfism is characterized by an extremely small thoracic cage with only eleven pairs of ribs present. Other physical characteristics of the disease are that the infant has a large skull relative to its face, which is often elongated with a prominent forehead. The eyes are widely spaced, and there is a broad, flat nasal bridge. Frequently, cleft palate is present. The ears are low-set and poorly formed, and the neck is short and fleshy. The limbs, particularly the legs, are bowed; clubfoot is common, as are dislocated hip joints.
A small percentage of short-statured individuals may be unusually short because of social and psychological factors. This condition is called psychosocial dwarfism. This type of nongrowth is secondary to emotional deprivation and is representative of a type of child abuse. The behavior of such children is characterized by apathy and inadequate interpersonal relationships, with inhibited motor and language development. They generally do not gain weight in spite of their extraordinary appetite and excessive thirst; such a child may steal and hoard food yet have the distended abdomen of a starving child. Diagnosis generally identifies a growth hormone deficiency, and when these children are moved to stimulating and accepting environments, their behavior becomes more normal. Their caloric intake decreases as their growth hormone secretion normalizes, and their growth undergoes a dramatic catch-up.
Because of the complications associated with some forms of dwarfism, medical counseling should begin early. A physical examination should take place in order to determine the type of dwarfism that the child has. If it is ascertained that the short stature cannot be treated, or if the parents and patient choose not to do so, they should be informed of the details of the patient's specific condition and cautioned regarding any future complications that may arise. The patient should be assured that intelligence will not be affected, even if the head is somewhat large. Ear infections are common, and the child should be closely monitored to prevent hearing loss. Normal fertility is the rule, but giving birth will necessitate a cesarean section. In many cases, the child will not be limited physically or mentally as he or she matures. The problems that the patient may face are usually social and emotional; for example, short-statured children may face bullying and discrimination. However, joining nonprofit groups that provide education and support to short-statured individuals may aid children and families in overcoming these difficulties.
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