Basic Science
DNA (deoxyribonucleic acid) is the hereditary material that contains the genetic information inherited by the offspring of an organism. It is a long molecule consisting of repetitive units of Adenine (A), Guanine (G), Cytosine (C) and Thymine (T). In human beings, it is arranged in the form of 23 pairs of chromosomes. Each pair comprises one chromosome from the father and the other from the mother.
A gene is a fragment of DNA that determines the physical appearance like height, hair, or eye color as well as dictates the various physiological processes in each human being. Sometimes it also determines what diseases a person is likely to get. A gene controls a hereditary characteristic and is responsible for the genetic transmission of most inherited traits.
A majority of the genes are the same in most people, but a small percentage of genes show differences among different people. Except for identical twins, all individuals show minor differences in the genetic information contained in their DNA (More than 99.9% of the DNA is same between any two individuals) and it is these small differences that are responsible for the uniqueness of every individual.
Genetics is the study of genes, heredity, and the variation of organisms. It determines most of the physical appearance and physiological properties of all organisms, including human beings. It accounts for both the similarities and differences between different organisms.
A genetic test examines the variations in an individual’s genes. It determines the genetic predisposition that a person has of developing a disease based on the DNA information of that person.
The Human Genome project was started in 1990 with the aim of identifying all the genes in the human DNA and determining the sequence of the approximately 3 billion nucleotides of which the human genome is comprised. After the release of the first draft sequence of the human genome in 2000, there has been an increased effort to look at this sequence information of different individuals in order to determine links between DNA sequence and disease. Studies have shown that a majority of the sequence is the same between any two human beings and only a very small fraction of the DNA shows differences in sequence. Knowledge about these differences in the DNA of different individuals can be used to obtain new methods for diagnosis, treatment and prevention of these diseases. The different variations of a single gene are called alleles. Alleles are responsible for the differences in the physiological and physical properties of each individual. Different alleles of a single gene are called gene variants or genetic variations. Basically, a genetic variation is the change in the sequence of bases in the DNA.
A genetic variant that occurs when there is a difference or change in a single base / nucleotide (A, T, G or C) within different members of a species is termed a single nucleotide polymorphism (SNP). When a single base change occurs in a population at a frequency of >1% is termed a SNP, while a base change that occurs at a frequency of <1% is considered to be a mutation. Since SNPs are inherited from one generation to the next without much change (ie. they are evolutionarily stable) and about 90% of all human genetic variations are SNPs, they extremely valuable in biomedical research. SNPs themselves do not cause diseases but they can help in determining the probability that an individual will develop a disease.
A genetic disorder is a disease caused due to variations in one’s DNA sequence.
Genetic Testing
A genetic test examines an individual’s DNA in order to look for variations in his genes. It determines the genetic predisposition that a person has of developing a disease based on the DNA information of that person.
The results of the DNA test as well as the information filled out in the nutrition and lifestyle questionnaire will be kept strictly confidential. The DNA sample is destroyed 14 days after the report is issued unless the candidate has voluntarily consented to storage / use of his/her genetic material for research. However if a medical doctor has ordered the test we also send a copy of the results to that doctor.
Histopathology confirms presence of disease. It helps in diagnosing the disease, its stage or severity. But it has limitations as far as treatment guidance is concerned. Genetic or marker tests help in assessing the genetic mutations (changes in gene sequence), expressions of genes in the tumor sample & accordingly it helps doctors to choose better treatment for the patient.
A family history is an indicative of you risk but it doesn’t tell you what you need to do to prevent conversion of this risk into disease. Moreover, family history is not the only cause for having these problems. It doesn’t tell any actionable preventive strategy. CVD (cardiovascular disease) is a complex disease, caused due to multiple genetic and environmental factors (diet, smoking, alcohol consumption, obesity, stress, etc). Routine diagnostic tests are excellent in diagnosing the acute as well as chronic disease. But those tests do not tell the cause of the problem. Also, the routine diagnostic measurements can vary based on the patient’s current environmental factors. Genetic test help in assessing the person’s risk at the gene level & also help in identifying the external factors that may also contribute to higher risk in the presence of these genetic factors.
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