What Your DNA Can Really Tell You

Do the offerings of companies like 23andMe cause more harm than good? Recently, genetic tests profiling health risks have come under fire. In November 2013, genetic screenings became a hot topic when the FDA sent a letter to the company 23andme stating the agency was “concerned about the public health consequences of inaccurate results.” The FDA said 23andMe’s product constitutes a medical device that must be approved by the agency. Since that warning, 23andMe has ceased selling the screening test. In December, an article ran in the New York Times titled “I Had My DNA Picture Taken, With Varying Results” that brought to light potential accuracy issues with genetic screening tests. The author found that her health risks for various diseases differed between the three companies she sent a DNA sample to. The tests screened for diseases such as obesity, rheumatoid arthritis, breast cancer and Alzheimer’s. Unfortunately, with all of the upset surrounding companies like 23andMe, information about screenings has become muddled and thrown more generally into genetic screenings of all kinds. Not all genetic screenings are created equal, and not all are fraught with the same accuracy issues that the New York Times author experienced. Genetic screening for breast cancer involves looking at two specific genes; BRCA1 and BRCA2. The screening looks for genetic abnormalities in those particular genes, and the results of the test can yield a positive result, a negative result, or an ambiguous or uncertain result. Many women with a familial history of breast cancer choose to screen for these mutations, and research indicates that the presence of these mutations significantly increases a woman’s risk for breast cancer1. In this case, researchers know the specific genes they need to look at closely, and so this makes genetic screening for breast cancer very different from the genetic screening done for overall disease markers. For pregnant women, prenatal screenings have become an important and routine part of prenatal care.

Since the 1970s, there have been great strides in prenatal testing technology. Prenatal tests have been developed for more than 800 genetic disorders. New techniques for amniocentesis have gradually improved the safety and accuracy of prenatal diagnosis. Amniocentesis utilizes a sample of amniotic fluid to detect chromosome abnormalities, neural tube defects and genetic disorders with high levels of accuracy (98-99%)2. Down syndrome, or Trisomy 21, is the most common chromosome abnormality.

Genetic disorders include disorders like cystic fibrosis. The most common neural tube defect is spina bifida. The procedure is invasive and does come with some risks, but for women who have genetic concerns, or familial history of any of those genetic disorders, it is usually a recommended course of action. Huntingdon’s Disease (HD) is an inherited neurological illness causing involuntary movements, severe emotional disturbance and cognitive decline. A single abnormal gene produces HD, and in 1993 scientists isolated that single gene on chromosome 4. At one end of the gene, a pattern of three DNA bases (CAG), or nucleotides, repeats itself in all cases. Using a blood sample, the genetic test analyzes DNA for the HD mutation by counting the number of CAG repeats in the huntingtin gene. In normal individuals, this tri-nucleotide, or triplet, repeat occurs between 11 and 29 times. In people with Huntington’s disease, the repeat occurs over and over again, from 40 times to more than 80. This genetic screening yields either a positive or negative result, and is close to 100% accurate—if it yields a positive result, you will begin to exhibit symptoms of HD later in life if you have not already. A positive result early in life enables individuals to make decisions about careers, marriage and families. While the tests 23andMe and other companies like them offer an overall snapshot of your future disease risk, much of what those screenings look for in the genetic code is not well known yet. The 23andMe test looks at only small segments of the DNA, called SNPs, and the test is limited to looking at less than a million SNPs (whereas the human genome has around 10 billion SNPs identified so far). To have your entire genome decoded would cost around $3,000 with current technology. The 23andMe test is different from looking at a specific gene, like BRCA1 or the gene that causes HD. It is important to know the differences between various types of genetic screenings, and understand the implications of the results.

Animal Rights National Conference 2018