The thymus gland is located behind the breastbone and is responsible for the maturation of T-cells to fight infections. The four parathyroid glands are located adjacent to the thyroid gland in the neck and regulate calcium in the blood through the production of parathyroid hormone.
DiGeorge syndrome is a genetic disorder with varying conditions present in each individual with the syndrome. However, conditions that are common to the syndrome include certain heart defects, effects on facial appearance, and lack of or underdeveloped thymus and parathyroid glands.
The history of the syndrome, previously referred to as DiGeorge, includes the following discoveries:
Velo-cardio-facial syndrome (VCFS) is a genetic condition that is related to DiGeorge syndrome. VCFS involves a similar chromosome abnormality as DiGeorge syndrome.
- In the 1970s, Robert Shprintzen, PhD, a speech pathologist, described a group of patients with similar clinical features including cleft lip and/or palate, conotruncal heart defects, absent or hypoplastic thymus, and some of these patients also had hypocalcemia. Dr. Shprintzen named this group of features velo-cardio-facial syndrome, but the syndrome was also referred to as Shprintzen syndrome.
- In the 1980s, the technology was developed to identify an underlying chromosome defect in these syndromes. It was determined that over 90 percent of all patients with features of DiGeorge, Shprintzen, and velo-cardio-facial syndromes had a chromosome deletion in the region of 22q11.2. In other words, this was the same syndrome, but because several different researchers in different areas of expertise had described it, the syndrome carried multiple names. Many physicians and researchers today use the term 22q11.2 deletion syndrome because it describes the underlying chromosome problem, or velo-cardio-facial syndrome (VCFS) because it describes the main body systems involved. However, for the purposes of this content, we will call it DiGeorge syndrome.
As mentioned, 90 percent of patients with the features of this syndrome are missing a small part of their chromosome 22 at the q11 region. This region encompasses about 30 individual genes and results in developmental defects in specific structures throughout the body. It is not known why this region of chromosome 22 is often deleted, but this is one of the most frequent chromosome defects in newborns. Deletion 22q11.2 is estimated to occur in one in 3,000 to 4,000 live births. Most of the 22q11.2 deletion cases are new occurrences or sporadic (occurs by chance). However, in about 10 percent of families, the deletion is inherited and other family members are affected or at risk for passing this deletion to their children. The gene is autosomal dominant, therefore; any person who has this deletion has a 50 percent chance of passing the deletion to a child. For this reason, whenever a deletion is diagnosed, both parents are offered the opportunity to have their blood studied to look for this deletion.
Approximately 10 percent of individuals who have the features velo-cardio-facial syndrome (VCFS) do not have a deletion in the chromosome 22q11.2 region. Other chromosome defects have been associated with these features, as have maternal diabetes, fetal alcohol syndrome, and prenatal exposure to Accutane® (a medication for cystic acne).
The following are the most common features of DiGeorge syndrome. However, not every child will have every feature of the syndrome and the severity of the features will vary between children. Features may include:
- palatal abnormalities (such as cleft lip and/or palate)
- feeding difficulties
- conotruncal heart defects (e.g., tetralogy of Fallot, interrupted aortic arch, ventricular septal defects, vascular rings)
- hearing loss or abnormal ear exams
- genitourinary anomalies (absent or malformed kidney)
- hypocalcemia (low blood calcium levels)
- microcephaly (small head)
- mental retardation (usually borderline to mild)
- IQs are generally in the 70 to 90 range
- psychiatric disorders in adults (e.g., schizophrenia, bipolar disorder)
- severe immunologic dysfunction (an immune system which does not work properly due to abnormal T-cells, causing frequent infections)
Facial features of children with DiGeorge syndrome may include the following:
- small ears with squared upper ear
- hooded eyelids
- cleft lip and/or palate
- asymmetric crying facies
- small mouth, chin, and side areas of the nose tip
The symptoms of DiGeorge syndrome may resemble of problems or medical conditions. Always consult your child's physician for a diagnosis.
In addition to a prenatal history, complete medical and family history, and a physical examination, diagnostic procedures for DiGeorge may include:
- blood tests and tests to examine for immune system problems
- x-ray - a diagnostic test which uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.
- echocardiography - a procedure that evaluates the structure and function of the heart by using sound waves recorded on an electronic sensor that produce a moving picture of the heart and heart valves.
- fluorescent in situ hybridization (FISH) studies - when features of conotruncal heart defects, clefting, other facial features, hypocalcemia, and absent thymus are identified, a blood test is usually ordered to look for a deletion in the chromosome 22q11.2 region. FISH is specifically designed to look for small groups of genes that are deleted. If the FISH test finds no deletion in the 22q11.2 region and the features of VCFS are still strongly suggestive, then a full chromosome study is usually performed to look for other chromosome defects that have been associated with this syndrome.
If a 22q11.2 deletion is detected in a child, then both parents are offered the FISH test to see if this deletion is inherited. In approximately 10 percent of families, the deletion has been inherited from one of the parents. Any individual who has this 22q11.2 deletion has a 50 percent chance, with each pregnancy, of passing it on to a child.
Specific treatment for DiGeorge syndrome will be determined by your child's physician based on the following:
- your child's age, overall health, and medical history
- the extent of the disease
- the type of disease
- your child's tolerance for specific medications, procedures, or therapies
- expectations for the course of the disease
- your opinion or preference
Treatment will also depend on the particular features in any given child and may include the following:
- Heart defects will be evaluated by a cardiologist.
- A plastic surgeon and a speech pathologist will evaluate cleft lip and/or palate.
- Speech and gastrointestinal specialists will evaluate feeding difficulties.
- Immunology evaluations should be performed in all children with this deletion. To monitor T-cell disorder and recurrent infections, live viral vaccines should be avoided and all blood products for transfusions (if needed) should be irradiated unless cleared by an immunology physician.
In severe cases where immune system function is absent, bone marrow transplantation is required.
Many newborns with this deletion will benefit from early intervention to help with muscle strength, mental stimulation, and speech problems. Basically, treatment is dependent upon the specific symptoms seen in any given child.
A small percentage of children with severe heart defects and immune system problems will not survive the first year of life. However, with the proper treatment of heart defects, immune system disorders, and other health problems, the vast majority of children with a 22q11.2 deletion will survive and grow into adulthood. These children will generally need extra help throughout school and will need long term care for their individual health needs.
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