No. DNA is a type of genetic material found in our cells and is made up of four types of DNA bases, represented by the letters A, T, C and G. The sequence, or order, of these bases determines an individual’s genetic code and carries genetic information. A “gene” is a segment of the DNA chain that carries specific genetic instructions for the body.
DNA bases are like letters in the alphabet while genes are like complete sentences or paragraphs that are made up of letters that convey a specific message through their sequence.
Yes. If we compare the genomes of two persons who are not related by blood, 99.9% of their genomes will be the same and only 0.1% of them will be different. However small this 0.1% might look like, it is significant enough to represent millions of differences in the two DNA sequences, accounting for each person’s unique physical characteristics.
Genetic variants are the differences in DNA sequences among us. Each person has millions of genetic variants, most of which are not disease-causing, but would make each of us have different physical characteristics, such as skin colour and height.
Genomic medicine is still a relatively new field of scientific research. While Whole Genome Sequencing enables us to read and sequence the over 3 billion DNA bases in a human genome, to enhance the diagnostic rate, finding out whether a genetic variant is linked with a disease requires research with a large number of clinical cases. It will take time and resources for healthcare professionals and scientists to conclusively identify disease-causing variants for many patients.
For the genetic testing products and services consumers purchase over the counter or online (Direct-to-consumer genetic tests, DTCGTs), some of them focus on specific areas without the use of Whole Genome Sequencing technology. The entire process, from publicity, marketing, to delivery of these products, is done directly by the service provider to the consumers. There may not be healthcare professionals involved.
From a medical point of view, the public should first consult healthcare professionals and obtain their assessment and opinion before deciding whether they should undertake any diagnostic or therapeutic investigation (including genetic testing).
There is a wide range of genetic testing services and products on the market, which can be categorised into two main types, health-related and non-health related.
Health-related genetic tests include:
- Diagnostic tests for heritable diseases (e.g. Cystic Fibrosis, Spinal Muscular Atrophy, etc.)
- Genetic susceptibility or predisposition testing for common and complex diseases (e.g. cancer, cardiovascular diseases, and diabetes, etc.)
- Carrier testing for genetic diseases inherited through X-linked recessive (e.g. Haemophilia) and autosomal recessive manner (e.g. Thalassaemia)
- Pharmacogenomic testing for guiding choice of medications and dosage
Non-health related genetic tests include:
- Ancestry
- Talents
- Athletic performance
- Fun traits (e.g. eye colour)
- Nutritional needs
Yes. Even if they test for the same disease, the tests provided by different service providers may differ, thus producing different results. Some genetic tests on the market might not be supported by adequate scientific and clinical evidence, resulting in variable levels of credibility, accuracy, uncertainty, and clinical utility. Seeking medical professionals’ opinion before conducting any tests can help you understand the clinical utility of the test results.
If the genetic test is done to diagnose a particular genetic disease, a positive result usually, though not always, means confirmation of diagnosis of a particular genetic disease, or prediction of its development in the future. However, in many circumstances the test result may not be able to predict disease severity and prognosis.
The interpretation of genetic susceptibility testing for common and complex diseases (e.g. cancer, high blood pressure and diabetes, etc.) has even greater uncertainty. The accuracy in predicting the development of such diseases, be it a positive or negative result, is usually even lower. Therefore, the clinical utility of such genetic susceptibility testing might also be limited.
When a test result is positive, the test subject should seek opinion from a medical specialist relevant to the particular disease as soon as they can.
A negative test result generally indicates that the test subject does not carry the genetic variants in question, but it does not entirely exclude the possibility of developing such disease. Uncertainty exists in all results, be it positive or negative, and its magnitude depends on various factors, including the complexity of the genetic disease, the testing technology adopted, the stringency of the testing procedures and so on. If genetic testing is accompanied by counselling and explanation on the results by healthcare professionals, you can gain a better understanding of the results and its potential impact.
From the medical perspective, you are recommended to consult healthcare professionals before undertaking any medical tests (including genetic test). They may arrange suitable tests based on the patient’s health condition and clinical assessment, and provide appropriate follow-up or treatment as needed.