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Revision as of 09:57, 27 August 2011
|Note - This page is an undergraduate science embryology student group project 2011.|
A congenital disorder is one which is present at birth. They are often abnormalities that arise from errors that occur during development of the fetus. Some congenital abnormalities are genetic, and often run in families while others are spontaneous and have no genetic linkages. DiGeorge syndrome is a congenital abnormality that is caused by the deletion of a part of chromosome 22. The symptoms and severity of the condition is thought to be dependent upon what part of and how much of the chromosome is absent. .
About 1/4000 children born are affected by DiGeorge syndrome, with 90% of these cases involving a deletion of a section of chromosome 22 . DiGeorge is quite often a spontaneous mutation, but it may be passed on in an autosomal dominant fashion. Some families have many members affected.
DiGeorge is a complex syndrome and patient cases vary greatly. The common symptoms present across numerous patients include
- Abnormal faces
- Congenital heart defects
- Hypoparathyroidism with hypocalcemia
- Cognitive, behavioral, and psychiatric problems
- Increased susceptibility to infections
- Hypoplasia or absence of the thyroid and parathyroid glands 
DiGeorge is a serious syndrome affecting many of the body systems. The clinical manifestations of the chromosome 22 deletion are significant and can lead to poor quality and a shortened lifespan for the patient. As there is currently no treatment education is vital to the wellbeing of those affected, directly or indirectly by this condition.  Current and future research is aimed at how to prevent and treat the condition, there is still a long way to go but some progress is being made.
- Angelo DiGeorge. In the mid 1960's, Angelo DiGeorge noticed a similar combination of clinical features in some children. He named the syndrom after himself. The symptoms that he recognised were hypoparathyroidism, underdeveloped thymus, conotruncal heart defects and a cleft lip/palate. 
- 'Robert Shprintzen described patients with similar symptoms (cleft lip, heart defects, absent or underdeveloped thymus, hypocalcemia) and named the group of symptoms as velo-cardio-facial syndrome. 
- 1980s technology develops to identify that these patients have part of a chromosome missing. 
It appears that DiGeorge syndrome has an incidence of about 1 per 2000-4000 live births in the general population, and frequently presents with cleft palate, as well as congenital heart defects. As would be suspected, it appears that cardiac complications are the largest causes of mortality. Infants face constant recurrent infection as a secondary result of T-cell immunodeficiency, caused by the hypoplastic thymus. There is no preference to either sex or race.
The presentation of more severe cases of DiGeorge syndrome is apparent at birth, especially with malformations. Within the first 6 months of life, susceptibility to infection may raise suspicion of DiGeorge syndrome. However, it has been well documented that there individuals who have relatively minor cardiac malformations and normal immune function, and may show no presentation of DGS until later in life, which may be resultant form a learning dysfunction.
As mentioned in the introduction, the pathogenesis of DiGeorge is a 22q11.2 microdeletion. More precisely, DiGeorge is a result of a 2-3million base pair deletion from the long arm of chromosome 22. It seems that this particular region in chromosome 22 is particularly vulnerable to microdeletion, which is a result of complications that occur during meiosis. It seems that multiple genes exist in this region, which results in similar symptoms being seen across a large number of 22q11.2 microdeletion syndromes. As mentioned previously, this means that all 22q11.2 microdeletion syndromes have very similar presentation, making the exact pathogenesis difficult to treat, and unfortunately DiGeorge syndrome is well known by several other names, including (but not limited to) Velocardiofacial syndrome (VCFS), Conotruncal anomalies facie (CTAF) syndrome, as well as CATCH-22 syndrome.
A specific gene that seems to be critical in DiGeorge syndrome is the TBX1 gene which, when deleted, causes the exact presentation of DiGeorge syndrome. The TBX1 chromosomal section results in the failure of the third and fourth pharyngeal pouches to develop, resulting in several signs and symptoms which are present at birth. These include thymic hypoplasia, hypoparathyroidism, recurrent susceptibility to infection, as well as congenital cardiac abnormalities, craniofacial dysmorphology and learning dysfunctions.
|Diagnostic Test||How it works||Relevance to DiGeorge|
|Fluorescence in situ hybridisation (FISH) ||FISH is a technique that attaches DNA probes that have been labeled with fluorescent dye to chromosomal DNA. When viewed under fluorescent light, the labelled regions will be visible. This test allows for the determination of whether or not chromosomes or parts of chromosomes are present. This procedure differs from others in that the test does not have to take place during cell division. ||FISH is a significant test used to confirm a DiGeorge diagnosis. Since the syndrome features a loss of part or all of chromosome 22, the probe will have nothing or little to attach to. This will present as limited fluorescence under the light and the diagnostician will determine whether or not the patient has DiGeorge. As with any testing, it is difficult to rely on one result to determine the condition. The patient must present with certain clinical features and then FISH is used to confirm the diagnosis.|
|Based on symptoms||DiGeorge patients often have similar symptoms even though it is a condition that affects a number of the body systems. These similarities can be used as early tools in diagnosis. Practitioners would be looking for features such as the following:
||When considering a patient with a number of the traditional symptoms of DiGeorge, a practitioner would not rely solely on the clinical symptoms. It would be necessary to undergo further tests such as FISH to confirm the diagnosis. In addition, with modern technology and prenatal care advancing, it is becoming less common for patients to present past infancy. Many cases are diagnosed within pregnancy or soon after birth due to the significance of the heart, thyroid and parathyroid.|
|Ultrasound||An ultrasound is a prenatal care test to determine how the fetus is developing and whether or not any abnormalities may be present. The machine sends high frequency sound waves into the area being viewed. The sound waves reflect off of internal organs and the fetus into a hand held device that converts the information onto a monitor to visualize the sound information. Ultrasound is a non-invasive procedure. ||Ultrasound is able to pick up any abnormalities with heart beats. If the heart has any abnormalities is will lead to further investigations to determine the nature of these. It can also be used to note any physical abnormalities such as a cleft palate or an abnormally small head. Like diagnosis based on clinical features, ultrasound is used as an early indication that something may be wrong with the fetus. It leads to further investigations.|
|Amniocentesis||Amniocentesis is a medical procedure where the practitioner takes a sample of amniotic fluid in the early second trimester. The fluid is obtained by pressing a needle and syringe through the abdomen. Fetal cells are present in the amniotic fluid and as such genetic testing can be carried out.||Amniocentesis is performed around week 14 of the pregnancy. As DiGeorge symdrome presents with missing or incomplete chromosome 22, genetic testing is able to determine whether or not the child is affected. 95% of DiGeorge cases are diagnosed using amniocentesis. |
|BACS- on beads technology||BACS on beads technology is a fast, cost effective alternative to FISH. 'BACS' stands for Bacterial Artificial Chromosomes. The DNA is treated with fluorescent markers and combined with the BACs beads. The beads are passed through a cytometer and they are analysed. The amount of fluorescence detected is used to determine whether or not there is an abnormality in the chromosomes.This technology is relatively new and at the moment is only used as a screening test. FISH is used to validate a result.||BACs is effective in picking up microdeletions. DiGeorge has microdeletions on the 22nd chromosome and as such is a good example of a syndrome that could be diagnosed with BACs technology. |
Further research possibilities
Autoimmune of or relating to disease caused by antibodies or lymphocytes produced against substances naturally present in the body (against oneself)
Congenital preset from birth
Facies appearance of facial expression of an individual that is typical for a particular disease or condition
Hypocalcaemia deficiency of calcium in the blood stream
Hypoparathyrodism diminished concentration of parthyroid hormone in blood, which causes deficiencies of calcium and phosphorus compounds in the blood and results in muscular spasm
Palate the roof of the mouth, separating the cavities of the nose and the mouth in vertebraes
Parathyroid glands four glands that are located on the back of the thyroid gland and secrete parathyroid hormone
Parathyroid hormone regulates calcium levels in the body
Renal of or relating to the kidneys
Schizophrenia a long term mental disorder of a type involving a breakdown in the relation between thought, emotion and behaviour, leading to faulty perception, inappropriate actions and feelings, withdrawal from reality and personal relationships into fantasy and delusion, and a sense of mental fragmentation. There are various different types and degree of these.
Thyroid Gland large ductless gland in the neck that secrets hormones regulation growth and development through the rate of metabolism
2011 Projects: Turner Syndrome | DiGeorge Syndrome | Klinefelter's Syndrome | Huntington's Disease | Fragile X Syndrome | Tetralogy of Fallot | Angelman Syndrome | Friedreich's Ataxia | Williams-Beuren Syndrome | Duchenne Muscular Dystrolphy | Cleft Palate and Lip