by John B. Carnett
We charged one worrywart writer, Michael Rosenwald, with getting as many different DNA tests as he could to find out what his future–or, more specifically, his genes–had in store for him. In a search for everything from cancer to narcolepsy, Rosenwald sent blood samples or cheek swabs to genetic-testing labs across the country. The DNA in the harvested cells was then extracted from the cells’ nuclei to undergo PCR amplification, essentially molecular photocopying. Once sufficient copies (at least one million, sometimes up to a billion) of the required DNA had been made, a variety of techniques were used to detect genetic variations. Here’s a rundown of the tests he took and how each test works.
Celiac Disease
What it tests for: Sensitivity to gluten-containing grains, like wheat
How it works: A patient’s DNA binds to a nylon strip if it contains DNA sequences that indicate susceptibility to celiac disease. When it binds, an enzymatic reaction occurs, turning parts of the strip purple. A specific pattern of purple bands indicates a predisposition to the disease.
CYP2D6
What it tests for: Ability to process drugs metabolized by CYP2D6-derived enzymes, including antipsychotics, heart medicines and pain medications
How it works: It searches for a duplication of a genetic sequence using PCR. If the resultant copy is unusually long, it indicates the presence of the duplication.
genelex.com
Cystic Fibrosis
What it tests for: Frequently fatal disorder that causes severe lung damage
How it works: A patient’s DNA is mixed with two fluorescently labeled complementary sequences. One binds to a sequence found in normal patients, and one–of a different size and color–binds only if the patient’s gene is mutated. A technician studies the size and color of the DNA product. Depending on the lab and the reagents used, long and green might mean healthy, while short and red might mean a mutation.
dnadirect.com
BRCA 1 and 2 for Breast and Ovarian Cancer
What it tests for: Breast and ovarian cancer in Ashkenazi Jews. It also has a weak correlation with incidences of prostate cancer and a very strong correlation with occurrences of pancreatic cancer
How it works: Each nucleotide base is tagged with a different color of fluorescent marker. The pattern created is compared with that of a normal gene. If the colors don’t match up, the gene has a variation.
dnadirect.com
Thrombophilia Panel
What it tests for: Inherited blood-clot disorders
How it works: If a restriction enzyme finds the normal sequence of DNA bases, it cuts the DNA chain into two pieces. If the code has changed as a result of genetic mutation, however, the DNA remains intact.
dnadirect.com
Hemochromatosis DNA
What it tests for: Iron-overload disorder
How it works: Uses the same technique as the thrombophilia panel.
kimballgenetics.com
Apo-e Genotype
What it tests for: Type III hyperlipoproteinemia, a lipid disorder
How it works: Uses the same technique as the thrombophilia panel to look at three different alleles.
kimballgenetics.com
Tay-Sachs
What it tests for: Fatal juvenile disorder that damages the central nervous system
How it works: Uses the same technique as the thrombophilia panel.
kimballgenetics.com
PST genetic
What it tests for: Predisposition to periodontal disease
How it works: Uses the same technique as the thrombophilia panel to look at two different alleles.
kimballgenetics.com
HLA-B27 DNA
What it tests for: Spondyloarthropathies, chronic inflammatory disorders
How it works: A specifically designed primer binds only to the mutant sequence of the DNA strand, causing the sequence to multiply. If the gene is normal, the primer cannot bind, and no amplification occurs.
kimballgenetics.com
Narcolepsy DNA
What it tests for: Excessive daytime sleepiness
How it works: Uses the same technique as the HLA-B27 test to look for narcolepsy-associated HLA alleles.
kimballgenetics.com
CYP2C19
What it tests for: Ability to process drugs metabolized by CYP2C19-derived enzymes, including antipsychotics and anti-inflammatories
How it works: Same as the HLA-B27 test.
genelex.com
CYP2C9
What it tests for: Ability to process drugs metabolized by CYP2C9-derived enzymes, including warfarin (Coumadin) and phenytoin (Dilantin)
How it works: Uses the same technique as the HLA-B27 test.
genelex.com