Array Comparative Genomic Hybridization

Normal human development depends on genes located along the chromosomes. Chromosomes are structures inside your cells that contain all of your genes. If you think of your DNA as a library, each chromosome is a book. Your genes are the chapters inside each book. Each chapter, or gene, contains specific instructions.

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Humans have two sets of 23 chromosomes, for a total of 46. There are 22 pairs of autosomes plus one pair of sex chromosomes (the X and Y chromosomes). We inherit one set of chromosomes from our mother and one set from our fathers. Typical female chromosomes are named 46, XX, and typical male chromosomes are 46, XY.

Losses and Gains of DNA

Sometimes, by chance, small pieces of chromosomes are lost (deleted) or doubled (duplicated). Chromosomes can also break and rejoin, which is called a translocation.

Chromosome changes can be large or small. Large rearrangements may be found by looking at a chromosome analysis like in the picture above. This test looks at the “big picture” and can find large changes very accurately. However, chromosome changes can be so small that they can’t be seen under the microscope. These kinds of changes are usually microdeletions and microduplications. Labs use an advanced testing technique called array comparative genomic hybridization (array CGH) to decide whether there certain regions are there or not. People who study genetics often group the gains and losses of DNA that can be found with array CGH as “copy number variants,” or just “CNVs.”

Depending on where these chromosome changes happen and how large they are, it may change a person’s genes. Having extra or missing copies of genes changes the way a person grows and develops. It may cause mental retardation, birth defects, and/or autism. Some changes have no effect at all.