|Circulating Cell-free Fetal DNA
|Early detection of Down syndrome from a maternal blood sample
|Genetic information to individualize medical care and drug treatment
|Direct to Consumer Genetic Testing
|Genetic analysis an individual obtains and pays for privately
|Whole Genome and Whole Exome Sequencing
|Disease discovery by analyzing every single gene an individual has
Circulating cell-free fetal DNA analysis:
We normally think of DNA as being contained in the nucleus of every cell (except for red blood cells, which have no nuclei). Those with more intimate knowledge of biology will add that there is also DNA within the mitochondria, which are structures in the cell which create energy from the foods we eat. But, the DNA in either case is contained within cells. It turns out there is a small amount of DNA in plasma (the fluid component of blood) that is not contained within cells. In the case of a pregnant woman, about 10% of that circulating cell-free DNA originates from the fetus. If the fetus has Down syndrome, which occurs when there are three chromosome 21's, rather than the usual two, there will be a slight excess DNA from chromosome 21 as compared to other chromosomes. This principle underlies a new screening test for Down syndrome, which is sometimes termed non-invasive prenatal testing, or circulating cell-free fetal DNA analysis.
Until recently, there was no easy way to determine the proportion of fetal DNA in a mother's plasma, nor could the ratio of chromosome 21 compared to other chromosomes be accurately determined. This has changed because of a newly developed technique called massively parallel sequencing, which effectively analyzes millions of DNA fragments and determines to which chromosome they belong and whether they are maternal or fetal in origin. Utilizing this technique, there are now four companies offering screening for Down syndrome (also called trisomy 21), trisomy 18 (three copies of chromosome 18), trisomy 13 (three copies of trisomy 13) and certain sex chromosome abnormalities (where there is not the normal two copies of the X chromosome for females or an X and a Y chromosome for males). The first company to offer this testing was Sequenom Center for Molecular Medicine (MaterniT21™). Other companies presently offering the test clinically are: Verinata Health(Verifii®) ; Natera (Panorama™) ; and Ariosa (Harmony™) . More details of the testing are on our web site. In the near future, it will be possible to use this same technique to look for other genetic conditions in a fetus as early as ten weeks gestation, without having to resort to procedures like amniocentesis or chorionic villus sampling, both of which are associated with a small risk of miscarriage.
As a side note, utilizing circulating cell-free DNA is not limited to pregnant women. Recurrence of certain cancers can be monitored by measuring whether there is circulating DNA with characteristic changes. And, this technique may eventually be used, for example, for colon cancer surveillance; a simple blood test has the promise to replace periodic colonoscopies.
Genetic variation influences the occurrence and severity of common diseases, such as heart disease, stroke, diabetes, Alzheimer disease, and cancer. However, unlike rare conditions such as cystic fibrosis, hemophilia, and sickle cell anemia, each of which is due to changes in a single gene, these common conditions are caused by interactions between multiple genetic, environmental, and life style factors.
Recent advances in genetic testing promise to offer information that will lead to more effective treatment and prevention of common diseases. Use of genetic testing for this purpose is often referred to as personalized medicine or precision medicine. While it is straightforward to perform extensive genetic analysis on an individual, oftentimes using an easy to collect sample of saliva, interpreting the results of genetic testing can be complicated.
In this very new field, the most established use of genetic testing is in providing assistance in drug selection and initial dosage for several types of medications. However, even for this limited indication, it is not clear how helpful this sort of genetic testing is or will be. Eventually, genetic testing for factors involved in heart disease, stroke, and Alzheimer disease may offer benefits. But, at present, more useful information can be obtained by careful family history and analysis of life style factors than can be gained by genetic testing.
Direct to consumer genetic testing:
Medical testing is normally ordered by a physician or other health professional and is performed in laboratories operating under federal (CLIA), professional (CAP), or state (e.g., New York State Department of Health) supervision. Direct to consumer (DTC) testing is, as its name implies, offered directly to individuals through advertisements on radio, television, print media, and the internet. Except in certain states, such as New York, companies are free to offer this "informational" testing with few restrictions. Since the testing is not considered medical diagnostic testing, laboratories may, but need not, conform to the same standards as are required for laboratories offering health professional-iniated testing.
In March of 2008 the Genetics and Public Policy Center identified 32 laboratories providing DTC testing for a variety of conditions, including: carrier screening for various types of genetic disorders; ancestry testing; risks for Alzheimer disease, cardiovascular disease, and diabetes; personal genome service; paternity testing; and nutrition/metabolic health. Only 27 labs were identified as of August 2011 by the same Center, including 7 laboratories requiring physician involvement. Several of those laboratories have either closed or merged with other organizations by April 2013, and some no longer offer DTC testing. One of the largest surviving companies providing DTC genetic testing, 23 and me, offers genetic testing for ancestry and health for $99 on a saliva sample. While their web site has extensive information and the quality of the laboratory analysis is very high, there is no evidence that this genetic information has a positive effect on health, including quality of life and life span. It is unclear whether there is a psychological benefit to having the genetic information, or conversely if the information may cause unnecessary anxiety or adversely influence medical treatment.
Paternity testing by genetic analysis is highly accurate in determining family relationships. Interpretation of the results of testing, unlike ancestry and health genetic testing, is usually straightforward. A number of companies offer paternity testing (see a list of New York State approved laboratories). In New York, this testing needs to be ordered by a health care professional.
Whole Genome and Whole Exome Sequencing:
There is a huge amount of information encoded in our DNA. However, interpreting that information, and using that information to improve our health and well being represents a challenge. Technology for DNA sequencing (i.e., determining the genetic code of an individual) is improving rapidly, and it is now possible to determine the entire genetic code of an individual at an affordable price ($1,000-$6,000 as of 2013). Furthermore, the cost of sequencing can be expected to decline in the future. The process of sequencing the entirety of an individual's genetic information is called whole genome sequencing. The genome represents the sum total of all the genes and additional information contained in the nucleus of each cell, and sequencing the genome produces a vast amount of genetic information.
About 1% of the DNA in the genome corresponds to known genes. This is called the exome. Whole exome sequencing is considerably less expensive than whole genome sequencing, and there is 100-fold less data to analyze than whole genome sequencing. At least six organizations presently offer this testing as a clinical service. Whole exome sequencing has already proven extremely useful in identifying genetic diseases that are rare, hard to diagnose, or have never been discovered. In particular, children with birth defects, developmental disability, growth disorders, or combinations of these may have a genetic disease that can be identified by this technique. Whole exome sequencing promises to make diagnoses of genetic disease more quickly and less expensively than conventional diagnostic testing (such as biopsies, CT scanning, blood tests, or testing of individual genes).
While individuals known or suspected to have a genetic disease may be candidates for whole exome sequencing, the benefit, if any, for healthy individuals to have whole gene or whole exome sequencing is not known. There are too many uncertainties at present to warrant performing such testing, except in carefully selected instances.