Gene Chips Detect Tiny Structural Defects in Genomic Diseases
Conditions that originate in alterations of chromosome architecture have been called "genomic diseases." The smallest of these structural defects are microdeletions, a loss of a small amount of genetic material, or microduplications, an excess of genetic material.
Individually, many genomic diseases are rare, but collectively, they may occur in one in 1,000 live births. Frequently the gene aberrations harm multiple organ systems. For example, patients with chromosome 22q11.2 deletion syndrome may have heart defects, impaired immunity and developmental delay. Deletions of several genes in Prader-Willi syndrome may cause obesity and mental retardation.
To seek out miniscule rearrangements in chromosomes, the Children's Hospital team employed the types of gene chips, or microarrays, originally designed to identify genes involved in common, complex diseases like diabetes and hypertension. Microarrays contain short fragments of DNA, called oligonucleotides, that bind to complementary stretches of DNA within a sample being tested. These microarrays hold more than 100,000 DNA oligonucleotides, which allow researchers to rapidly analyze a person's whole genome -- the entire complement of DNA in a cell nucleus.
"These microarrays provide more rapid and precise results than karyotyping, and offer as much as 50 times higher resolution than other, more commonly used microarrays, such as bacterial artificial chromosome arrays," said Dr. Shaikh. "Our study is one of the first to report using these microarrays in a clinical setting to detect constitutional rearrangements which lead to severe birth defects." Constitutional rearrangements occur in all of a person's cells.
As Technology Improves, Smaller Defects Should Be Detectable
In the current paper, the research team first validated the micr
Source:Children's Hospital of Philadelphia