Growth and Growth Disorders

Everyone has a different size and shape, and there is a wide range of what doctors consider normal growth. In order to monitor growth, doctors use an established range of normal heights and weights for different age groups. From the time a child first goes to the doctor, measurements of height and weight are taken. The doctor uses a growth chart to compare a child's height and weight growth rate with those of others the same age. As a newborn, everyone starts out at about the same size. Yet some end up short and some tall.

When developing a standard growth chart, researchers take a large number of children of different ages and make a graph of their heights and weights. The height at the 50th percentile means the height at which half of the children of that age are taller and half are shorter. The 25th percentile means that three-fourths (75%) of the children are taller at that age and one-fourth (25%) are shorter. The 75th percentile means that threefourths of the children (75%) are shorter and one-fourth (25%) are taller.

People vary greatly, and if children are between the 3rd and 97th percentile, and if they are growing at a normal rate, they usually are regarded as normal. If children are outside these ranges (over the 97th percentile or under the 3rd percentile), doctors may look for some explanation. Most often, these children simply have inherited “short” or “tall” genes * from their parents, and they will continue to grow at a normal pace. While adult height is related to the height of a person's parents, there is still much variation among siblings.

During adolescence, a growth spurt normally occurs. Generally, growth spurts for girls start about two years earlier than growth spurts for boys. Rates of growth and change during puberty vary with the individual. Parents' growth and puberty patterns often are passed on through their genes to their children: If one or both parents had a late puberty, then their children are more likely to reach puberty later and to experience a later growth spurt. The medical term for this “late bloomer” pattern is constitutional growth delay.

Children with precocious puberty experience early growth spurts due to the abnormally early rise in sex hormone levels in their bodies. Although initially this causes these children to grow taller than others their age, their skeletons mature more rapidly as well, often causing them to stop growing at an early age. If precocious puberty is left untreated, it may lead to a decrease in a child's ultimate height.

Growth occurs when bones of the arms, legs, and back increase in size. The long bones of the limbs have a growth plate at the end. The growth plate is made of cartilage, which is a tough, elastic tissue. Cartilage cells in the growth plate multiply and move down the bone to produce a matrix (tissue from which new bone is formed). These cartilage cells then die, leaving spaces. Special cells called osteoblasts (OS-tee-o-blasts), meaning bone beginners, then produce bone (by laying down the minerals calcium and phosphorus) to fill the spaces and replace the matrix. Once all the cartilage in the growth plate has been turned to bone, growth stops, which usually occurs before ages 16 to 18. An x-ray of the hand or knee can show the doctor the bone age (maturity of the bone) and how much potential growth remains.

Children with poor nutrition may have poor growth. A balanced diet with adequate protein is essential for normal growth. Some parts of the world have serious problems with malnutrition, and the growth of children may be affected in these areas.

Chronic diseases that may impair growth include diabetes * , congenital heart disorders, sickle cell anemia * , chronic kidney failure, and cystic fibrosis * .

Concurrent illnesses can bring a slowdown or stop in height increments. These involve two or more illnesses that would have little effect alone but cause serious problems when occurring together. These illnesses may be recognizable or may be too subtle for recognition.

One form of extreme short stature is caused by abnormal formation and growth of cartilage and bone. Children with skeletal dysplasia * are short and have abnormal body proportions. Their intelligence levels usually are normal. Most of these conditions are inherited or occur due to genetic abnormalities.

If growth in the uterus is interrupted while a fetus * is forming or developing, the condition is called intrauterine (meaning within the uterus) growth restriction (IUGR). IUGR is not the same as when a baby is born prematurely. The small size of a premature infant usually is normal according to the gestational (jes-TAY-shun-al) age (or the age from conception).

Failure to thrive (FTT), or inadequate weight gain any time after birth, may occur in infants. There are many possible causes, and the doctor must examine the child carefully. Often, the baby or child simply is not getting enough to eat. Sometimes other illnesses are interfering with weight gain that must be treated. Severe social deprivation such as occurs in an inadequate orphanage or institution can also lead to a slowdown or cessation of height gains.

Disorders of certain chromosomes * also can cause short stature. For example, Down syndrome, a condition that occurs when a person has three copies of chromosome 21, results in arms and legs that are shorter than usual. Another genetic condition, Turner syndrome, is caused by a missing or partially missing X chromosome. The average height of adult women with Turner syndrome is between 4 feet 6 inches and 4 feet 8 inches without treatment. Adolescent girls with Turner syndrome have underdeveloped ovaries.

Marfan syndrome is a hereditary condition affecting connective tissue and is associated with tall stature. People with Marfan syndrome have very long arms and legs, eye problems, and differences in facial features. Other physical problems, such as aortic aneurysms and other heart abnormalities, also may be present. It is commonly believed that Abraham Lincoln had Marfan syndrome.

Achondroplasia (a-kon-dro-PLAY-zee-a) is a genetic condition that affects the skeletal system and causes people to be unusually short. Gene mutations (changes) that cause achondroplasia can be spontaneous (not carried by the parents), and most people with achondroplasia are born to averagesized parents. In some cases, achondroplasia is inherited. The most common form of short stature, achondroplasia affects about 1 in 15,000 to 1 in 40,000 people, which translates to about 10,000 affected individuals in the United States. Worldwide, about 150,000 people have achondroplasia. The average adult height of people with achondroplasia is little more than 4 feet.

Unusually short stature and very short legs and arms are the most visible signs of achondroplasia. Some people are affected by other problems, which may include the following:

Once achondroplasia is suspected in a developing child (for instance because of outward appearance, failure to grow, or how bones look in x-rays), doctors look for the genes that cause achondroplasia. Administration of the growth hormone somatotropin is used to accelerate growth in individuals with achondroplasia. The most significant growth results occur within one year of the start of somatotropin treatment. Healthcare professionals recommend treatment with this hormone be started at an early age, preferably between the ages of one and six years, to derive maximum benefits from therapy. There have been no long-term studies to determine final height achievement capabilities or to justify long-term treatment with somatotropin. Treatments also involve resolving accompanying medical problems, such as surgery to alleviate joint discomfort.

Sometimes, people with achondroplasia opt for an experimental surgical procedure that lengthens the arms and legs. It involves cutting a bone, inserting a scaffold between the bone segments, and allowing new bone to grow and fill in the gaps. Limb-lengthening surgery is not a common treatment in the United States because it is controversial and painful, requires repeated surgeries, and can lead to complications, such as nerve damage.

Growth is controlled by hormones (chemical messengers) from various glands. An important growth hormone is secreted by the pituitary gland. The gland looks like a peanut sitting at the base of the brain. Other hormones are also essential for growth. The thyroid gland in the neck secretes thyroxine (thy-ROX-in), a hormone required for normal bone growth. Sex hormones from the ovaries (estrogen) and testicles (testosterone) are essential for the growth spurt and other body changes that occur during puberty.

The pituitary gland is attached by a stalk to the hypothalamus, an area of the brain that controls the function of the pituitary. The anterior or front part of the pituitary gland secretes the following hormones that can affect growth:

Sometimes the pituitary gland does not make enough growth hormone, a condition known as hypopituitarism, which usually slows a child's growth rate to less than 2 inches per year. The deficiency may appear at any time during infancy or childhood. When doctors have ruled out other causes of growth failure, they may recommend special tests for growth hormone deficiency. Children with growth hormone deficiency are treated with daily injections of the hormone, often for several years. With early diagnosis and treatment, these children usually increase their rate of growth and may catch up to achieve average or near-average height as adults.

In pituitary dwarfism, caused by low amounts of growth hormone, the person is short but has normal body proportions. This is different from other forms of dwarfism due to genetic skeletal dysplasia. In these cases, the person with dwarfism is short, and the growth of the arms, legs, torso, and head often is out of proportion. For example, the person's arms and legs may appear relatively smaller than the head or torso.

Two conditions arise from excessive amounts growth hormone (a condition known as hyperpituitarism) in the body: acromegaly and gigantism. The cause usually is a benign * pituitary tumor * .

Acromegaly, a condition caused by increased secretion of growth hormone after normal growth has been completed, occurs in adults. The condition is rare, occurring in 6 out of 100,000 people. Because the adult cannot grow taller, the excess growth hormone in acromegaly causes adult bones to thicken and other structures and organs to grow larger. Usually, excessive production of growth hormone begins between the ages of 30 and 50. After acromegaly has been diagnosed from a blood test that determines an elevated growth hormone level, an MRI * scan of the pituitary is used to locate and detect the size of the tumor causing the growth hormone overproduction.

Gigantism is abnormally large growth due to an excess of growth hormone during childhood, before the bone growth plates have closed (epiphyseal fusion). The vertical growth in height is accompanied by growth in muscle and organs. The result is a person who is very tall, with a large jaw, large face, large skull, and very large hands and feet. Many health problems may be associated with gigantism, including heart disease and vision problems. Untreated gigantism may lead to acromegaly. Delayed puberty also may occur in this condition. There is no one best treatment available to control excess growth hormone secretion. According to guidelines from the U.S. Endocrine Society, surgery to remove the pituitary gland tumor is considered the treatment of choice for acromegaly. If any residual tumor remains at 12 weeks after surgery, further treatment consisting of radiation therapy may be required. Patients should also be evaluated for the development of hypopituitarism due to damage to the pituitary gland from the tumor. Hormone replacement may be necessary if there is pituitary gland damage from the tumor or from the treatment.

The thyroid gland looks like a butterfly at the base of the neck. One wing is on one side of the windpipe or trachea, and the other is on the other side. The wings are joined by a thin strip of thyroid tissue. The thyroid gland makes the hormone thyroxine (thy-ROX-een).

The thyroid is controlled by the pituitary gland, which makes thyroidstimulating hormone. The hormone thyroxine controls the rate of chemical reactions (or metabolism) in the body. Too much thyroxine, or hyperthyroidism, speeds up metabolism.

The opposite condition is hypothyroidism, which is caused by the body's underproduction of thyroid hormone, and this condition affects many different body processes. A child with thyroid hormone deficiency has slow growth and is physically and mentally sluggish. The lack of this hormone may be present at birth if the thyroid gland did not develop properly in the fetus. Or the problem may develop during childhood or later in life as a result of certain diseases of the thyroid.

In most states, babies are tested for hypothyroidism at birth. Blood tests can detect the problem, and treatment usually is a daily pill that replaces the missing thyroid hormone. Early diagnosis and continuing treatment help these children grow and develop normally.

The adrenal glands, which are located on top of the kidneys in the abdomen, secrete the hormone cortisol. If too much cortisol is made by the child's adrenals, or if large doses of the hormone are given to the child to treat certain diseases, Cushing's syndrome may develop. Children with this syndrome grow slowly, gain weight excessively, and may experience delayed puberty due to the effects of the abnormally large amounts of cortisol in the body.

There are many causes for growth problems. To detect these disorders early it is important for doctors to track growth carefully in infants and children. Many of these conditions can be treated effectively, resulting in more normal adult heights for children with growth disorders.

See also Birth Defects: Overview • Brain Tumor • Cushing's Syndrome • Cystic Fibrosis • Dietary Deficiencies • Down Syndrome • Fetal Alcohol Spectrum Disorders (FASD) • Genetic Diseases: Overview • Heart Disease, Congenital • Hormone-Secreting Tumors • Hydrocephalus • Marfan Syndrome • Metabolic Disease • Puberty and Sexual Development • Thyroid Disease • Tumor • Turner Syndrome