Thymic aplasia

Related Terms

22q11.2 deletion syndrome, abnormal facies, cardiac defect, cardiac outflow, cell-mediated immunity, chromosome 2q11, congenital heart defect, cytokines, DGA, DiGeorge anomaly, echo, echocardiogram, fetal alcohol syndrome, fluorescent in situ hybridization (FISH) studies, genetic disorder, genetic test, heart defect, hereditary, hypocalcemia, hypoparathyroidism, immune, immune defense system, immune reaction, immune response, immune system, immunocompromised, immunodeficiency, infection, inherited disorder, primary immunodeficiency, right-aortic arch, T cells, T lymphocytopenia, thymic, thymocytes, thymus, thymus gland, truncus arteriosus, underactive parathyroid, underactive thymus, VCFS, velocardiofacial syndrome, weakened immune system.

Background

DiGeorge syndrome (DGS) is named after Dr. Angelo DiGeorge, who first described the disease in the 1960s. Dr. DiGeorge was the first to demonstrate the role of the thymus in immune function. He described four cases in involving infants with thymic hypoplasia, hypoparathyroidism, and recurrent infection.
DiGeorge syndrome (DGS), also called DiGeorge anomaly or thymic aplasia, is an immune system disorder that occurs when the thymus gland is absent or not fully developed. Patients are born with this disorder.
The thymus gland is responsible for producing a type of white blood cell called T cells, which help the body fight against disease and infection. When the thymus gland is absent or underdeveloped, not enough T cells are produced. Therefore, patients with DGS syndrome are vulnerable to infections.
This disorder is also associated with other developmental defects, including abnormalities of the heart and large blood vessels around the heart and face. In addition, DGS patients often have hypoparathyroidism (underactive parathyroid glands), and the esophagus (the tube that leads from the mouth to the stomach) is typically underdeveloped.
Depending on how underdeveloped the parathyroid gland is, some patients may experience low calcium levels in the blood, which may lead to seizures. This is because the parathyroid gland is partially responsible for regulating the body's calcium levels.
The condition is caused by a genetic defect. DGS patients are missing a specific region on chromosome 22 that contains approximately 30-40 genes. The chromosomes contain the genetic makeup of an individual. Genetic research has identified one particular gene deletion on chromosome 22, TBX1, which is thought to be responsible for many of the features of DGS. In addition the same region of chromosome 22 also contains the COMT gene, and a deletion in this region is thought to contribute to the psychiatric complications of the disease. In a minority of cases, the defect is inherited (passed down from parents to their children). In most cases, patients are born without the gene by chance.
Researchers estimate that about one out of 3,000-4,000 individuals worldwide are born with DGS. Men and women are equally affected by DGS.
The disorder is usually diagnosed soon after birth because of the distinct physical defects and heart abnormalities associated with it.
There is currently no cure for DiGeorge syndrome (DGS). Thymus gland and bone marrow transplants have been conducted, with varying effectiveness. Patients typically receive supplements with calcium and vitamin D to manage their underactive parathyroid glands.
The prognosis varies among patients. In approximately 1% of cases, the thymus is completely missing. Some patients who have partial DGS may experience spontaneous T cell improvement and parathyroid function. However, most patients with complete DGS die within the first six months of life. Most deaths are the result of heart defects. Infections caused by severe immune deficiency are the second most common cause of death.

Author information

This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography

Hollander G, Gill J, Zuklys S, et al. Cellular and molecular events during early thymus development. Immunol Rev. 2006 Feb;209:28-46. .
Immune Deficiency Foundation. .
Machado AM, Simon TJ, Nguyen V, et al. Corpus callosum morphology and ventricular size in chromosome 22q11.2 deletion syndrome. Brain Res. 2007 Feb 2;1131(1):197-210. Epub 2006 Dec 13. .
National Primary Immunodeficiency Resource Center. .
Natural Standard: The Authority on Integrative Medicine. .
Wurdak H, Ittner LM, Sommer L. DiGeorge syndrome and pharyngeal apparatus development. Bioessays. 2006 Nov;28(11):1078-86. .

Causes

DiGeorge syndrome (DGS) occurs when patients are missing part of chromosome 22. Chromosomes contain an individual's genetic makeup. This particular chromosome contains about 30-40 genes that are necessary for proper fetal development. When this chromosome is missing, patients are born with the developmental defects characteristic of DGS.
This defect can be inherited or it may occur by chance. When DGS is inherited, it is passed down as an autosomal dominant trait by the parents. This means that individuals develop the disorder if they inherit one mutated gene from either parent. Parents who have the disease have a 50% chance of passing the disease on to each of their children.
An estimated 90% of DGS cases occur by chance (which is called de novo). It remains unknown exactly why this chromosome is susceptible to deletion from the genetic code. Some studies suggest that there is a correlation between fetal alcohol syndrome and DGS. However, further research is necessary to determine whether or not these two conditions are related.

Diagnosis

General: DiGeorge syndrome (DGS) is usually diagnosed soon after birth because of the distinct physical defects and heart abnormalities that are associated with the disorder. If DGS is suspected, a blood test will indicate abnormalities in the levels of white blood cells. The standard diagnostic tool for DGS is genetic testing is called a fluorescent in situ hybridization (FISH) study. Once DGS is diagnosed, an echocardiogram can be performed to detect abnormalities of the heart. Pregnant women who are concerned that their babies may have a genetic immune disorder may undergo amniocentesis or chorionic villus sampling.
Blood test: A blood test will detect low or nonexistent levels of T cells and increased levels of B cells in the blood. In healthy individuals, T cells make up 68-75% of all white blood cells, while B cells make up 10-20% of all white blood cells.
Echocardiogram: An echocardiogram is used to detect abnormalities in the patient's heart. During the procedure, which is performed at a hospital, three flat, sticky patches, called electrodes, are attached to the patient's chest. These electrodes are attached to an electrocardiograph monitor, which records the electrical activity of the heart. The healthcare provider will then rub a wand called a sound-wave transducer over the patient's chest. This produces images of the heart on the electrocardiograph monitor, and the healthcare provider is able to detect abnormalities. This painless and noninvasive procedure generally takes about 40 minutes.
Fluorescent in situ hybridization (FISH) studies: A fluorescent in situ hybridization (FISH) study is used to determine whether the patient is missing certain regions of chromosome 22. During the procedure, which is performed at a genetic testing laboratory, a sample of the patient's blood is taken. The blood sample is then fluorescently stained. This causes the chromosomes in the blood to glow under ultraviolet light. The scientist is then able to detect chromosomal abnormalities. Patients who are missing all or part of chromosome 22 are diagnosed with DGS.
Prenatal DNA analysis: Pregnant mothers may have their unborn children tested for the disorder. In order to retrieve a sample of the fetus's cells for testing, amniocentesis or chorionic villus sampling may be performed. During amniocentesis, a long, thin needle is inserted into the pregnant woman's abdominal wall to the uterus. A small amount of fluid is removed from the sac surrounding the fetus. During chorionic villus sampling (CVS), a small piece of tissue (called chorionic villi) is removed from the placenta. There are risks associated with these procedures, including miscarriage. Patients should discuss the potential risks and benefits of these procedures with their healthcare providers.

Treatment

General: There is currently no cure for DiGeorge syndrome (DGS). Supplements with calcium and vitamin D are used to manage an underactive parathyroid gland. A bone marrow transplant may help boost the immune system. Early thymus transplantations are controversial, because their safety and effectiveness remain unclear.
Bone marrow transplant (BMT): Bone marrow transplants (BMTs) have been conducted, with varying results. In studies, some patients experienced a boost in their immune systems after a BMT. However, it is unknown whether these patients had partial DGS. Patients who have partial DGS may experience spontaneous improvements in T cell functioning.
Calcium supplements: Calcium supplements are typically given to patients who have an underactive parathyroid gland. Calcium gluconate (Kalcinate?) has been administered intravenously (injected into the vein) to prevent seizures associated with low levels of calcium. Alternatively, calcium carbonate (Os-Cal?, Titralac?, Oystercal,? or Caltrate?) has been taken by mouth.
Early thymus transplant: It remains unknown whether an early thymus transplant is safe and beneficial for patients with DGS. During this procedure, the thymus gland of a fetus is surgically transplanted into a young DGS patient. The transplanted thymus tissue is taken from a newborn who received heart surgery. During heart surgery, a small amount of thymus tissue must be removed in order for the surgeon to reach the heart. Instead of discarding the thymus tissue, it can be transplanted into a newborn with DGS. It is recommended that the transplant be conducted before complications of infections develop.
Patients who have partial DGS do not require thymus transplants because their T cells may spontaneously improve.
Vitamin D supplements: Vitamin D supplements are typically given to patients who have an underactive parathyroid gland. Supplementation with vitamin D helps the body absorb more calcium, which subsequently helps prevent seizures in DGS patients. A liquid solution called ergocalciferol (vitamin D2) (Drisdol?) has been taken by mouth along with calcium supplements.

Integrative therapies

Note: Currently, there is insufficient evidence available on the safety and effectiveness of integrative therapies for the prevention or treatment of DiGeorge syndrome. The therapies listed below have been studied for related conditions, including seizure-related conditions, hypoparathyroidism, pseudohypoparathyroidism, and immune-related conditions. The therapies listed below should be used only under the supervision of a qualified healthcare provider and should not be used in replacement of other proven therapies or preventive measures.
Strong scientific evidence:
Vitamin D: The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D aids in the absorption of calcium, which may prevent seizures. High oral doses of the vitamin D analogs dihydrotachysterol (DHT), calcitriol, and ergocalciferol can assist in increasing serum calcium concentrations in people with hypoparathyroidism or pseudohypoparathyroidism.
Vitamin D is generally well tolerated in recommended doses; doses higher than those recommended may cause toxic effects. Vitamin D is considered safe in pregnant and breastfeeding women when taken in recommended doses. Use cautiously with hyperparathyroidism (overactive parathyroid), diabetes, low blood pressure, kidney disease, liver disease, or granulomatous disorders (a type of immune disorder), or in mothers who are receiving vitamin D supplements and who are breastfeeding. Avoid if allergic or hypersensitive to vitamin D or any of its components, or with vitamin D hypersensitivity syndromes. Avoid in patients with hypercalcemia (high blood calcium levels).
Good scientific evidence:
Calcium: Calcium is an alkaline earth metal and is the most abundant mineral in the body. Patients who have an underactive parathyroid gland have problems regulating the amount of calcium in the blood, resulting in low levels of calcium. Supplementation with calcium may decrease the risk of seizures. According to case reports, nutritional deficiencies, including low levels of calcium, may lead to changes in the electrical patterns of the brain and may increase the risk of seizures. Correcting calcium to normal levels in cases of hypocalcemia (low levels of calcium in the blood) may be necessary. Further research is warranted.
Avoid if allergic or hypersensitive to calcium or lactose. High doses taken by mouth may cause kidney stones. Avoid with hypercalcemia (high levels of calcium in the blood), hypercalciuria (high levels of calcium in urine), hyperparathyroidism (high levels of parathyroid hormone), bone tumors, digitalis toxicity, ventricular fibrillation (when the ventricles of the heart contract in an unsynchronized rhythm), kidney stones, kidney disease, or sarcoidosis (inflammation of lymph nodes and various other tissues). Calcium supplements made from dolomite, oyster shells, or bone meal may contain unacceptable levels of lead. Use cautiously with achlorhydria (an absence of hydrochloric acid in gastric juices) or arrhythmia (irregular heartbeat). Calcium appears to be safe in pregnant or breastfeeding women, who should talk to a healthcare provider to determine appropriate dosing.
Ginseng: The predominant pharmacologically active constituents of Panax are ginsenosides. Individuals with an absent or underdeveloped thymus gland have a weakened immune system and are prone to infections. Ginseng seems to stimulate T cell and polymorphonuclear (PMN) leukocyte activities, increase clearance of bacterial infections treated with antibiotics, and improve the immune response to, and efficacy of, influenza immunization.
Use cautiously in patients taking agents that raise or lower blood pressure, in patients with diabetes or hypoglycemia or those taking agents that affect blood sugar, in patients with immune disorders or those using immunosuppressants, in patients using agents that may increase the risk of abnormal heart rhythms, in patients with fair skin or those using light-sensitizing agents, in patients with mental health disorders, in patients taking opiates, in patients prone to seizures, in patients using alcohol, in patients with sleep or "heat" disorders, and in children. Use cautiously during the perioperative period. Avoid in patients with bleeding disorders or those taking agents that may increase the risk of bleeding. Avoid in patients with known allergy or sensitivity to Panax species, their constituents, or to other members of the Araliaceae family. Avoid in pregnant or breastfeeding women. Avoid use of large amounts in infants. Over-the-counter combination products containing ginseng may be contaminated with phenylbutazone and aminopyrine.
Probiotics: Probiotics are beneficial bacteria (sometimes referred to as "friendly germs") that help to maintain the health of the intestinal tract and aid in digestion. Probiotic bacteria have been found to stimulate the body's immune system.
Probiotics are generally considered safe and well tolerated. Use cautiously in patients prone to infections or those with compromised immune systems, such as those with HIV/AIDS, or in infants born prematurely or those with immune deficiency. Use cautiously in patients with gastrointestinal disorders or in those sensitive or intolerant to dairy products containing probiotics or to lactose. Avoid with known allergy or sensitivity to probiotics.
Zinc: Zinc is necessary for the functioning of more than 300 different enzymes and plays a vital role in a large number of biological processes. Its immune-enhancing activities include regulation of T lymphocytes, CD4 cells, natural killer cells, and interleukin-2. In addition, it has been claimed that zinc possesses antiviral activity. Zinc gluconate appears to have beneficial effects on immune cells.
Zinc is generally considered safe when taken at the recommended dosages. Use amounts regularly exceeding the recommended upper tolerance levels (greater than 40 milligrams daily) under a physician's guidance only. Use cautiously in patients with bleeding disorders, diabetes, or low blood sugar levels, or in patients taking agents for these conditions. Use cautiously in patients with high cholesterol or blood fats, a high risk of developing heart disease, various skin disorders, gastrointestinal disorders, liver disease, genitourinary conditions, blood disorders, neurological disorders, pulmonary or respiratory disorders, immune disorders, or kidney disease, or in patients taking antidepressants, potassium-sparing diuretics, antibiotics (particularly tetracyclines and quinolones), iron, penicillamine, thyroid hormones, or copper. Avoid in patients who are homozygous for hemochromatosis (a metabolic disorder involving the deposition of iron-containing pigments in the tissues and characterized by bronzing of the skin, diabetes, and weakness) or with a known allergy or hypersensitivity to zinc compounds. Avoid use of intranasal Zicam?.

Prevention

Currently, there is no known method to prevent DiGeorge Syndrome (DGS).
Patients should take precautions to avoid contracting infections associated with the disease, such as thoroughly washing their hands with soap and water. Patients should talk to their healthcare providers about recommended immunizations. Patients should avoid close contact with individuals who have contagious illnesses, because they have an increased risk of contracting infections.
Patients who have the disorder may wish to receive genetic counseling. A counselor will provide information and answer questions about the risk of passing the disorder on to the patient's children.

Signs and symptoms

DiGeorge syndrome (DGS) is categorized as (1) complete (an absence of the thymus gland), (2) partial (a severely underdeveloped thymus gland), or (3) transient (a mildly underdeveloped thymus gland). Congenital (present at birth) heart disease is common among patients. A minority of patients experience no heart problems.
Common physical defects associated with DGS include increased space between the eyes, an upward slant of the eyes, large ears that are lower than normal with a notched ear fold, unusually small jaws, a cleft in the lip, a high arched palate, nasally speech, conotruncal heart defects, hearing loss, mental retardation, an absent or malformed kidney, low levels of calcium in the blood, a small head, and psychiatric disorders in adults (such as schizophrenia or bipolar disorder).

Complications

Infections: Individuals with an absent or underdeveloped thymus gland have a weakened immune system, because this gland produces important white blood cells called T cells. Therefore, patients with DiGeorge syndrome (DGS) are susceptible to infections that may be fatal. Patients may experience chronic runny nose, recurrent pneumonia, oral thrush (yeast infection of the mouth), and diarrhea. Patients are generally weak and may also be susceptible to sudden death.
Seizures: DGS patients typically have underactive parathyroid glands. These glands regulate the calcium levels in the blood. Therefore, DGS patients usually have calcium deficiencies, which may lead to seizures.
Psychiatric abnormalities: Behavioral abnormalities, including shyness, disinhibition, attention-deficit disorder, and autism spectrum disorders, have been reported in DGS patients. A higher incidence of psychoses, including anxiety, bipolar disorder, depression and anxiety, is observed in DGS patients, with a prevalence estimated at 10%.