• MICROARRAY CGH
  
  The C.A.R.E Clinic (South Africa) led by Dr Ramdeo have accomplished another milestone by achieving their first CGH pregnancy, believed to be the first in Africa and South Africa. The patient who is currently 15 weeks pregnant has polycystic ovarian disease (PCOS) and endometriosis. Her husband presented with a severe sperm factor problem (severe oligospermia) with spermatogenic arrest due to contracting chicken pox as an adult. The couple have been trying to conceive for 6 years and were successful in falling pregnant on their first IVF treatment at C.A.R.E Clinic.
   
   
  This advance in technology could bring hope to many couples struggling to have a baby and going through many IVF cycles.
   
   
  What is microarray comparative genomic hybridization (CGH)?
   
   
  Microarray CGH is an advance in technology and is a new and accurate screening test that detects a loss or gain of chromosomes. It is more sensitive than the standard test (FISH) which has the limitation of only testing 4 or 5 chromosomes at a time. Microarray CGH can analyze all 46 chromosomes in a single test and may discover an abnormality that would not have been detected by FISH.
   
  To understand how microarray CGH works, you have to understand a little about DNA, genes and chromosomes.
   
   
  What is DNA?
   
  DNA (deoxyribose nucleic acid) is life’s genetic code that enables various cells to develop and work together to form a fully functional body, and controls characteristics such as eye colour. The information in DNA is stored as a code in the nucleus of a cell and is made up of four different chemical bases. The bases are adenine (A), thymine (T), guanine (G) and cytosine (C). Because of their chemical nature, A will link with T and G will link with C.
  
  
  
  What is a gene?
   
  A gene is a unit of heredity in a living organism. It is a short piece of DNA that tells the body how to build a specific protein. Genes are your body’s instruction manual and also passes genetic traits to offspring. Humans have more than 30 000 genes.
  
  
  
  What is a chromosome?
   
  A chromosome is a structure that contains tightly packaged DNA and genes. Humans have 46 chromosomes made up of 23 pairs. A mother passes 23 chromosomes to her child through her egg and a father passes 23 chromosomes through his sperm. There is one pair of sex chromosomes (two X chromosomes for females and one X and one Y chromosome for males) and 22 pairs of autosomes (non-sex chromosomes). Any alteration in the number of chromosomes can be attributed to changes that can occur during the formation of reproductive cells (eggs and sperm), in early foetal development or in any cell after birth. Aneuploidy is a chromosome loss or gain and the term euploid refers to a complete set of 46 chromosomes.
  
   
  How does microarray CGH work?
   
   
  Microarray CGH compares the egg or embryo’s DNA with a control (normal) DNA sample and identifies differences between the 2 sets of DNA. In this way, a loss or a gain of chromosomes in the egg or embryo DNA can be identified. The embryo DNA and control DNA are combined with green and red dye respectively and placed onto a microarray slide containing thousands of spots of human genes corresponding to specific regions of chromosomes for analysis. The slide is scanned and the red to green ratio will determine if the DNA is normal or if there is a loss or gain of chromosomes. Euploid (normal) embryos are then selected and transferred improving the chances of a successful pregnancy.
  
  
  
  Who should have microarray CGH testing?
   
   
  Microarray CGH is suitable for all patients. Microarray CGH is helpful in younger women to diagnose the cause of repeated miscarriage, failed IVF or unexplained infertility. In most cases, it is the egg, rather than the sperm that determines the chromosomal integrity of the embryo.  In older women approaching the age of 40, the number of eggs produced with abnormal chromosomes increases. These eggs will produce abnormal embryos. However if the normal embryos are identified, there is a higher chance that can result in a successful pregnancy. Also, the risk of miscarriage increases with advanced maternal age.
   
  Microarray CGH is suitable for men who have been shown to have sperm at risk of carrying abnormal chromosomes, couples who have had a previous pregnancy with abnormal chromosomes or a child with birth defects as well as those with an inherited genetic disorder.
  What samples are needed for microarray CGH testing?
   
  Microarray CGH uses single cells (polar bodies and blastomeres) as well as multiple cells (trophectoderm).
   
   
   
   
  What are the advantages and limitations of microarray CGH?
   
   
  Microarray CGH testing provides the most comprehensive analysis of chromosomes to date. All 46 chromosomes can be analyzed in a single test. Euploid (normal) embryos can be selected improving the chance of a successful pregnancy for couples.
   
   
  The limitations of microarray CGH is that this test does not detect balanced chromosome translocations. This is because balanced chromosome translocations do not result in any loss or gain of chromosomal material. Microarray CGH cannot detect tiny changes such as a single base pair deletion.
   
  Microarray is available at the C.A.R.E Clinic – the first in South Africa and globally the first in Africa.
  
  

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