Array Comparative Genomic Hybridization (aCGH)
The array comparative genomic hybridization (aCGH) is a test used to assess gene problems associated with deletions, duplications, copy number variants (CNVs), and aneuploidies. This test is used as a baseline genomic screen to identify genes of interest and to detect submicroscopic abnormalities of genes.
Also called comparative genomic hybridization and chromosomal microarray analysis, aCGH is a method for identifying problems of each pericentromeric region along the chromosome. This test is used for screening, diagnosing, and treating certain developmental delays, autism spectrum disorders, and congenital anomalies. More than 70 conditions and disorders are caused by duplication or deletion of genomic material. These abnormalities are called ‘copy number variants’ or CNVs, and aCGH will detect CNVs.
What is the significance of aCGH?
Genetic alterations contribute to tumorigenesis, and these alterations could change gene expression, such as survival pathways and normal growth control. Comparative genomic hybridization is based on measuring DNA copy number of a target gene, to identify abnormalities. aCGH is a comprehensive tool that enables the detection of all clinically relevant imbalances in the genome, but it has limitations in the identification of polyploidy and balance translocations.
What is the purpose of the aCGH?
The array comparative genomic hybridization (aCGH) is done for research of genomic copy number change, which is for identifying structural variations with populations or disease cohorts, as well as to develop a cell line copy number variant profile. For a baseline genomic screen, this test is used to detect gene abnormalities and to identify deleted or amplified genes. When used in conjunction with g-banded karyotyping, the aCGH is used to define translocation breakpoints.
Which chromosomes are tested using comparative genomic hybridization?
aCGH allows for testing all 46 chromosomes. As with other types of preimplantation genetic diagnosis (PGD), the aCGH has limitations. An embryo may be labeled as normal with this test when it is abnormal (false negative), or the embryo may be considered abnormal when it is, in fact, a normal specimen (false positive).
What are the benefits of aCGH?
The main benefit of the comparative genomic hybridization test is that it can diagnose a number of abnormalities in the embryo, which is due to testing all 23 pairs. In addition, with this technology, pregnancy rates are 60-70% per cycle. In addition, the miscarriage rate using aCGH is less than 5%, as many miscarriages are related to chromosomal abnormalities of the embryo.
Why test for abnormal embryos?
Aneuploidy (abnormal embryos) are the cause of around 60% of miscarriages. One out of every three embryos are abnormal, so aCGH is a necessary test. To test the embryos so the embryologist can pick the best ones for transfer, aCGH is used. With in vitro fertilization (IVF), embryos are graded by viewing under the microscope. However, aCGH allows determination of the embryos with chromosomal abnormalities.
Who needs aCGH?
Chromosomal genomic hybridization is a good test for women who:
- Have a history of recurrent miscarriages.
- Are 35 years of age and older.
- Have had multiple failed IVF cycles.
- Have a previous pregnancy involving a chromosomal abnormality.
- Are carriers of a specific genetic condition.
- Have a partner with a genetic disorder.
- Have a long history of unexplained infertility.
How is the aCGH testing performed?
After the egg is fertilized using standard laboratory IVF procedures, a biopsy is performed on day 5 or day 6 of development. The cells are examined for abnormalities using a specific genetic laboratory method.