Achondroplasia

Achondroplasia

Definition

Achondroplasia, or short-limb dwarfism, is the most common form of

abnormally short stature in adults. It is caused by a mutation in a single gene

on chromosome 4 that regulates the conversion of cartilage to bone. This

gene is the only gene that is known to be associated with achondroplasia.

Description

Achondroplasia is basically a disorder of bone development. The skeleton

of a human fetus is composed primarily of cartilage, a dense and somewhat

elastic form of connective tissue that gradually turns to bone during

normal development. In a person with achondroplasia, a gene that is

involved in the process of bone formation produces too much of a protein

that limits bone growth. As a result, the person with achondroplasia has

unusually short bones in the arms and legs and other skeletal abnormalities.

They also usually have difficulties with posture, joint disorders, and

breathing problems in later life.

Demographics

Researchers estimate that achondroplasia occurs in one in every 15,000 to

40,000 live births. About 20 percent of cases are children who have one

parent with achondroplasia; however, 75

mutations of the gene responsible for the disorder.

These new mutations are more likely to occur in

the sperm of fathers over 35; the mother

not matter, as far as is presently known.

The disorder affects both sexes and all races

equally.

The average adult height of people with achondroplasia

is 4 feet 4 inches (1.3 meters) for men and

4 feet one-half inch (1.24 m) for women. The

shortest living person with achondroplasia as of

2008 was Jyoti Amge, a teenager from Nagpur,

India, who stands 23 inches (58 centimeters) tall

and weighs 11 pounds (5 kilograms).

’s age does

Causes and Symptoms

Achondroplasia is caused by a mutation in the

FGFR3 gene on chromosome 4. A normal gene

helps the body convert cartilage to bone. The

mutation in the gene related to achondroplasia

results in severely shortened bones and weak

muscle tone in the body.

The symptoms of achondroplasia are usually obvious by the first year

of life. They include:

•

Poor muscle tone.

•

walk until some point between 24 and 35 months.

Slowness in learning to walk; a child with achondroplasia may not

•

(temporary slowing or stopping of breathing), and overcrowding of

the teeth.

Abnormal skull structure leading to frequent ear infections, apnea

•

underdevelopment of the nose and midface.

Distinctive facial features, particularly a prominent forehead and

•

finger, giving the hand a distinctive trident (three-pronged) shape.

Greater than normal separation of the little finger from the ring

•

A tendency toward obesity.

•

in the lower back and bowed legs.

Postural problems, including a pronounced curvature of the spine•

Diagnosis

Babies with achondroplasia can be diagnosed before birth by ultrasound

measurements of the growth of their long bones and head size. After

birth, the diagnosis is usually based on x-ray studies of the child

and head size. The x-ray images usually reveal a small skull base, shortened

growth plates in the long bones, square-shaped long bones, and

normal-sized bones in the trunk area.

A genetic test can also be performed to confirm the diagnosis in children

whose symptoms may be less clear.

Treatment

The management of achondroplasia includes careful monitoring of the

child

charts that doctors use to evaluate the rate of growth in children with

achondroplasia. It is particularly important to prevent obesity if possible.

In addition, children with achondroplasia need social support because of

ongoing prejudice against people with dwarfism. Organizations such as

Little People of America can offer helpful advice on the education and

other future plans of children with achondroplasia.

Surgery may be performed if necessary to relieve pressure on the spinal

cord or the brain. In some cases, there may be a buildup of fluid in the

brain (hydrocephalus) that needs to be drained surgically. The child

and adenoids may be removed in order to lower the risk of apnea. The

shape of bowed legs can be corrected surgically, but doctors disagree about

the value of surgery intended to lengthen the legs.

Children with achondroplasia may need extra dental work because of

the mismatch between the size of their teeth and the size of the jaw. In

addition, they should be watched carefully for recurrent ear infections in

order to minimize the risk of deafness and later learning difficulties.

There is disagreement among doctors as of the early 2000s regarding

treatment with human growth hormone. It is considered an experimental

treatment. Many doctors are concerned that using growth hormone in

children with achondroplasia will lead to abnormal bone deposits and

worsening of the spinal curvature.

’s growth, head size, and weight pattern. There are special growth’s tonsils

Prognosis

The prognosis of a baby with achondroplasia depends on whether the

defective gene is inherited from only one parent or from both. A child

who inherits the gene from both parents will die before birth or shortly

after birth from respiratory failure. About 3 percent of children with

achondroplasia die suddenly and unexpectedly during the first year of life,

usually from compression of the spinal cord.

A child who has one normal copy of the gene will usually have

normal intelligence and a normal life expectancy in spite of bone and

joint problems.

Prevention

There is no known way to prevent achondroplasia because the gene

responsible for the condition can undergo mutation in families with no

history of the disorder, and 75

mutations.

–80 percent of cases result from new

The Future

Although new mutations of the gene associated with achondroplasia

cannot always be foreseen, people who have the condition should seek

genetic counseling before marriage. If the partner does not have the

mutation, there is a 50 percent chance with each pregnancy that the child

will have achondroplasia. If both spouses have the mutation, they have a

25 percent chance of a normal child with each pregnancy, a 50 percent

chance that the child will have achondroplasia, and a 25 percent chance

that the child will die before or shortly after birth.

SEE ALSO


Childhood obesity; Ear infection; Gigantism; Hydrocephalus’s bonesBack and leg pain in adult life.–80 percent of cases involve new