Dear Grandma,
Our body has tissues and organs that are made up of different types of cells. Each cell contains the deoxyribonucleic acid also known as DNA. This double-stranded DNA is made up of 4 chemical molecules also known as bases: adenine (A), guanine (G), cytosine (C) and thymine (T). In the DNA, A always pairs with T; C always pairs with G. These strands are nothing but sequences of these bases that run really long. So typically a short sequence of DNA if written down in English will read:
AGTCCCGGTTC
TCAGGCCAAG
The DNA sequences are 99% alike in all humans, but 1% unique. These sequences contain the genes characterized by a start point and an end point within the sequence that contain instructions for production of specific proteins, which in turn gives us a unique physical trait, for example: our height. The DNA is distributed on chromosomes. We have a total of 23 pairs of or 46 chromosomes, half of which comes from the mother and the other half from the father. (Help Me Understand Genetics, 2013).
There are specific gene sequences for genetic diseases like Huntington’s disease, Cystic fibrosis, dystonia, hemophilia, fragile X syndrome, etc (Javitt & Hudson, 2006). Normally, our DNA does not produce the proteins that cause such genetic diseases. However, when the gene sequence is altered or mutated (due to unknown biochemical, chemical or biological factors) even by one single base (for example, A instead G or C instead T), the DNA sequence changes, thereby production of a faulty protein that causes a genetic disease. These genes can be identified using test kits that are commercially available. However, they are not very reliable and you also do need your doctor to interpret the results properly. How do these kits work? Commercial test kits usually look for markers specific for the genetic disease of your interest. After years of research, scientists have predicted the exact locations of many genes identifiable by their base sequence and are called as markers. Genetic markers are specific gene sequences with known location on a chromosome and are used to identify physical traits, ethnicity, ancestry, detecting certainty or likelihood of genetic diseases, etc (Help Me Understand Genetics, 2013). For example, let’s take Huntington’s disease (HD). It was identified by group of scientists in 1983 that gene for HD is present on chromosome number 4. In its normal condition the gene produces a protein that is associated with proper functioning of neurons. A defective gene has stuttering (repetition of a certain base sequence) of CAG sequence (CAGCAGCAGCAG) that produces excess of an amino acid (building block of protein) glutamine. This glutamine accumulation results in a defective ‘huntingtin’ protein. This causes physical symptoms of HD such as jerky limb movements, balance problems, involuntary movements, deterioration of cognitive ability, etc (Burgunder, 2013).
There are 2 types of commercial genetic disease testing kits: predictive and predisposition genetic tests. Predictive tests are used for diseases that are caused by a single gene mutation such as HD and cystic fibrosis. Here, the kits use markers specific for the one mutated gene sequence that is characteristic of the genetic disease (stuttering or base change). If the disease is detected at an early stage, it can be either prevented altogether from manifesting itself or slowed down. On the other hand, predisposition test kits are used for diseases that are hereditary in nature, but cannot be predicted using only one gene mutation. For example: type 2 diabetes, cardiovascular diseases, etc. These tests take into account a number of factors (family history and lifestyle) along with the gene mutations across many genes associated with the disease of interest (Nance, Myers, Wexler & Zanko, 2003).
Few years back, genetic testing could only be done through healthcare providers, doctors and genetic counselors. After the advent of direct-to-consumer (DTC) genetic testing kits, consumers feel free to test themselves for probable genetic diseases that run in their families. The accuracy of such home-genetic kits is questionable, as not all of these kits qualify the regulatory standards (like that of the CLIA - Clinical Laboratory Improvement Amendments). The validity depends on the lab conditions and accuracy of the tests performed (Help Me Understand Genetics, 2013). The interpretation of the results needs to be done by a healthcare professional to understand the implications and manifestations of a genetic disease (Lloyd, 2012). However, if DTC genetic testing kits help a consumer make informed decisions regarding their life, it might be seen as a positive trend. Nevertheless, getting tested under the supervision of a trained professional will have a far greater validity and weightage for making life-changing decisions.
Lastly, being a firm believer of science, I will get myself tested for possible heritable and incurable genetic diseases through my healthcare provider. And if I did get tested positive, I will try not to have kids so as not to pass on the same to my children. I hope I have answered all your questions and hope you too make an informed decision!
References
- Burgunder, J. M. (2013). Translational research in Huntington's disease: opening up for disease modifying treatment. Translational neurodegeneration, 2(1), 2-2.
- Genetics Home Reference. (2013). Help me understand genetics: Genetic testing, US National Library of Medicine
- Javitt, G. H., & Hudson, K. (2011). Federal neglect: regulation of genetic testing. Issues in science and technologies, 22(3), 59-66.
- Lloyd, J. (2012, April 23). Genetic testing and disease: Would you want to know? USA Today
- Lloyd, J. (2012, June 7). Genetic testing: Does kristen powers have mom's fatal gene? USA Today
- Nance, M., Myers, R., Wexler, A., & Zanko, A. (2003).Genetic testing for Huntington's disease: its relevance and implications (revised). Huntington’s Disease Society of America.
