November 20, 2008

DiGeorge syndrome

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Definition

DiGeorge syndrome is a disorder present at birth (congenital) caused by problems within a developing embryo that occur due to chromosome defects. The specific chromosome defect your baby has dictates the medical concerns he or she will face.

Doctors sometimes refer to DiGeorge syndrome as velocardiofacial syndrome because problems frequently associated with the disorder include cleft palate (velopharyngeal incompetence), cardiac defects and abnormal facial features. Other common problems include immune system defects and low blood-calcium levels.

There's no cure for DiGeorge syndrome, and the long-term outlook for children with DiGeorge syndrome varies widely, depending on the organs affected. Treatment of DiGeorge syndrome focuses on correcting or managing the medical problems caused by the chromosome defect.

Symptoms

Infants with DiGeorge syndrome often have distinct facial features, including:

* Wide-set eyes
* Low-set ears, with a notched ear fold
* Small jaw
* A narrow, short groove in the upper lip

Other signs and symptoms of DiGeorge syndrome include:

* Cleft palate
* Recurrent infections, such as chronic runny nose or multiple bouts of pneumonia, oral thrush (candidiasis), diaper rash or diarrhea
* Cramp-like spasms of the baby's hands and fingers, or twitches or spasms of the muscles in the baby's face, throat or arms (tetany)
* Developmental delays, most often speech delay
* Slow mental development
* Lack of appetite
* Poor weight gain
* Failure to thrive

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Causes

The cause of DiGeorge syndrome is problems in the chromosomes within a baby's cells. Most babies born with DiGeorge syndrome are missing part of chromosome 22. Rarely, there may be other chromosome abnormalities that cause DiGeorge syndrome, such as a defect in chromosome 10. Sometimes babies with DiGeorge syndrome have no detectable chromosome abnormality.

Usually, the chromosome abnormalities related to DiGeorge syndrome aren't inherited. Instead, they happen spontaneously during embryonic development. The reason why these chromosome abnormalities occur isn't clear.

When portions of chromosome 22 are missing, it can affect the parts of the body the chromosome is responsible for developing, which include the following:

* Thymus gland. Part of your immune system, the thymus gland is a small organ located in your upper chest beneath your breastbone. During childhood, white blood cells called T lymphocytes (T cells) develop in the thymus and are distributed to your lymph nodes to help fight infection. After puberty, other parts of your body become more important in making and distributing T cells. As you grow, the thymus decreases in size and is slowly replaced by fat tissue. Defects in chromosome 22 may cause your baby's thymus gland to be smaller than normal (hypoplastic). In some cases, children with DiGeorge syndrome don't have a thymus gland.
* Parathyroid glands. You have four parathyroid glands in your neck, next to your thyroid gland. These small oval-shaped glands are each about the size of a pea. They maintain proper levels of calcium and phosphorus in your body by turning the secretion of parathyroid hormone (PTH) off or on. DiGeorge syndrome can be associated with parathyroid glands that are smaller than normal, which usually causes lower than normal secretion of PTH (hypoparathyroidism). Hypoparathyroidism often results in low levels of calcium (hypocalcemia) and high levels of phosphorus in the blood (hyperphosphatemia).
* Heart outflow vessels. Outflow vessels are the blood vessels that transport blood away from your heart. The largest is the aorta. Babies with DiGeorge syndrome frequently have heart defects associated with heart outflow vessels. The most common defects include: tetralogy of Fallot, ventricular septal defect, interrupted aortic arch, truncus arteriosus and patent ductus arteriosus In some infants, these defects may cause signs and symptoms such as shortness of breath, lack of appetite and poor weight gain.
* Facial features. Chromosome 22 is involved in the development of your facial bones, as well as your lips and ears. Defects in chromosome 22 cause the distinct facial features of DiGeorge syndrome. In some cases, the chromosome defects may also cause an opening or split in the roof of the mouth (cleft palate).

Risk factors

In most cases, researchers don't know what causes the chromosome abnormalities that result in DiGeorge syndrome. In a small percentage of cases, DiGeorge syndrome may be inherited from a parent, so a family history of the disease may increase a baby's risk of developing DiGeorge syndrome.

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