Digeorge Syndrome: A Study in Chromosomal Errors

DiGeorge Syndrome: A Study in Chromosomal Errors

DiGeorge syndrome is an anomaly that occurs when the 22q11.2 chromosome has been deleted, causing many different symptoms in various parts of the body. Those affected by DiGeorge syndrome often display signs of heart disease and defect at birth, presence of "cleft" palate (opening in the roof of the mouth), learning disorders, autoimmune diseases (such as rheumatoid arthritis), hypocalcaemia (low presence of calcium in blood), speech disabilities, and sometimes growth disorders. This syndrome is not explicitly fatal, but cardiac disorders caused by the DiGeorge syndrome are its greatest cause of mortality. Diseases contracted from severe immunity deficiency can also lead to death. It has been recently estimated that the DiGeorge syndrome and the deletion of the 22q11.2 chromosome occurs in 1 in 3000 births worldwide.

The DiGeorge Syndrome is caused by the deletion of material in Chromosome 22. Effects of this syndrome are also affected by how much genetic material is lost or deleted. The most logical explanation for this anomaly is its loss during genetic recombination, or "crossing-over". During Metaphase I of Meiosis, the chromosomes cross over DNA, creating more genetic variability, but an error occurs. Genetic material in the 22q11.2 chromosome is destroyed, causing an error during the development of the zygote, and causing such symptoms as described before. This syndrome is inherited in families through and "autosomal dominant" pattern, where there is a 50% change that the offspring will contract the syndrome from the parent(s). Chromosome 22, one of the first chromosomes to be fully sequenced by the Human Genome Project, is the targeted chromosome in this syndrome. The deletion of genetic material occurs in the middle region of the right arm, known as q11.2. The deletion of this region causes a loss of certain important genes. The gene TBX1 is responsible for many symptoms of the DiGeorge syndrome, mostly with cardiac disorders, cleft palate, altered facial features, and hypocalcaemia. The loss of another gene, COMT, may be the cause for behavioral problems and mental retardation. DiGeorge is a classic example of disorders and what disruption in the human genome can ultimately result in.