DiGeorge syndrome


DiGeorge syndrome

Description, Causes and Risk Factors:

A condition arising from developmental failure of the third and fourth pharyngeal pouches, resulting in the absence or underdevelopment of the thymus and parathyroid gland, associated with abnormalities of the outflow tract of the heart, distinctive facies, hypoparathyroidism, hypocalcemia with tetany, and deficiency in T-cell immunity; this is a contiguous gene deletion syndrome involving chromosome 22q11; autosomal dominant inheritance.

DiGeorge syndrome is a rare congenital (i.e. present at birth) disease whose symptoms vary greatly between individuals but commonly include a history of recurrent infection, heart defects, and characteristic facial features.

DiGeorge syndrome is caused by a large deletion from chromosome 22, produced by an error in recombination at meiosis (the process that creates germ cells and ensures genetic variation in the offspring). Most, but not all patients with the DiGeorge Syndrome have a small deletion in a specific part of chromosome number 22 at position 22q11.2. Another name for this syndrome is the chromosome 22q11.2 deletion syndrome. Patients with the DiGeorge Syndrome do not all show the same organ involvement. A given organ may be uninvolved, or so mildly involved that the organ appears to be normal. Thus, patients with the DiGeorge Syndrome may not all have the same organs involved or the same severity.

Although researchers now know that the DGS gene is required for the normal development of the thymus and related glands, counteracting the loss of DGS is difficult. Some effects, for example the cardiac problems and some of the speech impairments, can be treated either surgically or therapeutically, but the loss of immune system T-cells (produced by the thymus) is more challenging and requires further research on recombination and immune function.

Having a child with DiGeorge syndrome is challenging. You must address numerous treatment issues, manage your own expectations and meet the needs of your child. Organizations such as the Velo-Cardio-Facial Syndrome Educational Foundation provide educational materials, support groups and other resources for parents of children with DiGeorge syndrome.

Symptoms:

DiGeorge syndrome

Signs and symptoms may include some combination of the following:

    Bluish skin due to poor circulation of oxygen-rich blood (cyanosis).

  • Weakness or tiring easily.

  • Failure to thrive.

  • Failure to gain weight.

  • Poor muscle tone.

  • Shortness of breath.

  • Twitching or spasms around the mouth, hands, arms or throat (tetany).

  • Frequent infections.

  • Difficulty feeding.

  • Delayed development, such as delays in rolling over, sitting up or other infant milestones.

  • Delayed speech development.

  • Learning delays or difficulties.

  • A gap in the roof of the mouth (cleft palate) or other problems with the palate.

  • Certain facial features, such as low-set ears, wide-set eyes or a narrow groove in the upper lip.

Diagnosis:

The diagnosis of the DiGeorge Syndrome isusually made on the basis of signs and symptomsthat are present at birth or develop soonafter birth. Some children may have the facialfeatures that are characteristic of the DiGeorgeSyndrome. Affected children may also show signsof low blood calcium levels as a result of theirhypoparathyroidism. This may show up as lowblood calcium on a routine blood test, or the infantmay be “jittery” or have seizures (convulsions) asa result of the low calcium. Affected children mayalso show signs and symptoms of a heart defect.They may have a heart murmur that shows upon a routine physical exam, they may show signsof heart failure, or they may have low oxygencontent of their arterial blood and appear “blue” orcyanotic. Finally, affected children may show signsof infection because of the underdevelopment oftheir thymus gland and low T-lymphocyte levels.

Some children have signs or symptoms at birth orwhile they are still in the hospital nursery. Othersmay not show signs or symptoms until they area few weeks or months older. Some children andadults are diagnosed at a much older age dueto speech delay, qualitative speech problems, orfeeding problems.

There is a great deal of variation in the DiGeorge Syndrome from child to child. In some children, all of the different organs and tissues are affected. These children have the characteristic facial characteristics, low blood calcium from hypoparathyroidism, heart defects and a deficiency in their T-lymphocyte number and function. In other children, all of the different organs and tissues may not be affected, and the organs and tissues that are affected may be affected to different degrees.

Not only do children with the DiGeorge Syndrome differ in the organs and tissues that are affected, but they also differ in terms of how severely a given organ or tissue is affected.

In the past, the diagnosis of the DiGeorge Syndrome was usually made when at least three of the characteristic findings described above were present. Unfortunately, this caused many mild cases to be missed. In recent years, the genetic test has been more widely used. Over 90% of patients with the clinical diagnosis of DiGeorge Syndrome have a small deletion of a specific portion of chromosome number 22 at position 22q11.2. This can be identified in a number of ways, but the most common way is a FISH analysis (fluorescent in situ hybridization). Use of a FISH analysis test has made the diagnosis of DiGeorge Syndrome more precise and more common. Approximately 1 in 4000 babies have DiGeorge Syndrome or chromosome 22q11.2 deletion syndrome. For patients who do not have the deletion, the diagnosis continues to rely on the characteristic combination of clinical features.

Treatment:

Therapy for DiGeorge syndrome is aimed at correcting the defects in the organs or tissues that are affected. Therefore, therapy depends on the nature of the different defects and their severity.

Treatment of the low calcium and hypoparathyroidism may involve calcium supplementation and replacement of the missing parathyroid hormone. A heart (or cardiac) defect may require medications or corrective surgery to improve the function of the heart. If surgery is required, the exact nature of the surgery depends on the nature of the heart defect. Surgery can be performed before any immune defects are corrected. It is important that all the precautions that are usually taken with children with T-cell immunodeficiencies be observed, such as irradiating all blood products to prevent graft-versus-host disease and ensuring the blood products are free of potentially harmful viruses.

As mentioned above, the immunologic defect in T-lymphocyte function varies from child to child. Therefore, the need for therapy of the T-lymphocyte defect also varies. Many children with the DiGeorge Syndrome have perfectly normal T-lymphocyte functions and require no therapy for immunodeficiency. Other children initially have mild defects in T-lymphocyte function which improve as they grow older. In most cases of the DiGeorge Syndrome, the small amount of thymus that is present provides adequate T-lymphocyte function.

Rarely, the thymus is so small that adequate numbers of T-cells do not develop. In these cases, a special form of bone marrow transplantation or a thymus transplant may be performed.

In some children with the DiGeorge Syndrome, the T-lymphocyte defect is significant enough to cause the B-lymphocytes to fail to make sufficient antibodies. This occurs because antibodies are produced by B-lymphocytes under the direction of a specific subset of T-lymphocytes. When the B-cells are affected, this most often results in a delay in the production of antibodies. Rarely, children may require immunoglobulin replacement therapy (IRT).

As described in the preceding paragraphs, not all children with DiGeorge Syndrome require therapy for their immunodeficiency. Approximately 80% of the patients with the chromosome 22q11.2 deletion have diminished T-cell numbers. However, less than 0.2% have an immunodeficiency that requires a bone marrow transplant or a thymus transplant. The majority of children with an immunodeficiency have a mild-to-moderate deficit in the number of T-cells. These patients usually do not require transplantation; however, strategies aimed at prevention of the bacterial infections can often be quite helpful. This may include antibiotic prophylaxis and adequate treatment of any allergies. Allergies appear to be increased in patients with the DiGeorge Syndrome. They may contribute to the infections and are treated with the same medications used in other patients with allergies.

Approximately 10% of patients with the chromosome 22q11.2 deletion, and an unknown number of patients with the DiGeorge Syndrome without the deletion, have an autoimmune disease. This occurs when the immune system makes a mistake and tries to fight its own body. It is not known why this happens in people with T-lymphocyte problems. The most common autoimmune diseases in the DiGeorge Syndrome are idiopathic thrombocytopenia purpura (antibodies against platelets), autoimmune hemolytic anemia (antibodies against red blood cells), juvenile/adult arthritis and autoimmune disease of the thyroid gland.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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