A human body is made up of trillions of cells. Each cell shares one of the same similarity is that it contains a set of genetic components in the nucleus that codes for a human body, they are the deoxyribonucleic acid (DNA). There's an exception for mature red blood cells which do not have nucleus. Besides coding for human physical appearance, the DNA also controls how our bodies behave and react to different situation and environment. The DNA works by coding for particular functioning proteins or enzymes which commence specific action respectively.
Each person has his or her own unique set of genetic codes except for genetically identical twins. These genetic codes are inherited from both father and mother in the form of two sets of chromosomes. There are 23 pairs of chromosomes in a human body. However, not all of the genes in the chromosomes are expressed in every cell. Besides the housekeeping genes which are generally expressed in almost every cell where these genes are essential for the cell's survival, the other genes are only expressed selectively which give rise to specific characteristics to different type of cells (bone cells, neuron cells, etc).
As stated earlier that our genes control our body's behavior and reactions to different stimuli, it is all done through the regulation by the proteins encoded by the genes. How well our body resists bacterial infections, how much and how long should the hormones be released in our body, these are all depending on the proteins encoded by the genes, which are in the correct concentration and applied at the right part of the body. Any changes to the amount or the conformation of the proteins might cause disorders and some may be fatal. A mutated gene (alteration to the DNA sequence) might be the cause to this problem.
A gene can be mutated in various ways and they are all due to the alteration of DNA sequence. It may be due to a single change to a nucleotide (as seen in sickle cell anaemia), loss or gain of a nucleotide, or a whole change of a segment of a chromosome. The alteration of the DNA sequence may lead to the modification of the protein sequence, unless the mutation is silent where the translated protein is not affected, which change the conformation of the protein and in some cases may render the protein non-functional. In the case of sickle cell anaemia, the hemoglobin is still functional but in a reduced function state due to a single change to an amino acid. Gene mutation can be generally categorized to two types: germline mutations and somatic mutations.
In germline mutation, this disorder is inherited from the parents and can be continually passed on to the next generations. The mutation is copied every time the body cell divides and can be found in the reproductive cells, this type of cell mutation exists in the whole body of the affected person.
In somatic mutations, this disorder arises from individual cell in a certain time of a person's life and only passed on to the cells in direct relation during mitosis so this disorder do not affect the next generation. The somatic mutation may be caused by radiation or toxins which lead to the DNA being altered. This type of mutation is the common cause of cancer where the cell is unable to repair the damaged DNA sequence.
Previously, there's a statement on a human body has chromosomes in pairs (23 pairs in total), this applies to the genes too, where each gene inherited from father and mother respectively. These pairs of genes are known as alleles. They are normally differentiated to dominant and recessive allele. Dominant allele tends to overshadow over the recessive allele. If the dominant allele is deleted or somehow deactivated, the recessive allele prevails.
The characteristic of the alleles give rise to a number of situations of disorder in genetic disease. If the recessive allele contains the mutated gene, with the presence of normal dominant allele, the effect of recessive allele is suppress and the person is known as a carrier because the person still able to pass the defected gene to his/her offspring. To express the effect of the recessive allele, both recessive alleles must be present or the recessive allele stands alone without the presence of the dominant allele. On the other hand, in the case of the defected dominant allele, the effect of the allele will still be expressed no matter which partner allele it is paired to.
However, if a person is predicted to have defected alleles expressed, there's a factor called penetrance that indicates only a certain percentage of probability that the defected alleles to be fully expressed. Take for example the gene responsible for breast cancer (BRCA1), the risk of disease by age around 70 is 71%, not 100%. In certain cases, genetic disease needs two or more mutated genes to be expressed for example the Alzheimer's disease.
In order to diagnose whether a person is having a genetic disease, we could not only depend on the diagnosis of the sign and symptoms. With the advanced biotechnology nowadays together with the information from the "Human Genome Project", genetic testing is becoming a more feasible method to diagnose genetic disease. The disease can be diagnosed way before the sign and symptoms appear, even during the eight-staged cells after fertilization. This is because gene testing involves examining DNA from cells for any abnormalities; the cells are normally obtained through the blood samples.
Genetic testing is used for various purposes for example: screen the unborn babies for any traces of possible genetic disease, test for genetic disease to make necessary preparation before symptoms appear, confirming diagnosis of patients who has the disease symptoms.
With genetic testing, a person can know in advance if they are affected with any genetic disease. If they are diagnosed positive for certain disease, the person can make arrangement to prevent the onset of the disease; to recognize the disease at an early stage and to cure the disease if the cure is available; to make certain life decisions such as family planning.
To further explain the previously stated benefits; if a person who is in a high risk family happens to be tested negative, one would not need to undergo one's regular check up and save cost and time; if a person is tested positive for the genetic disease, specific regular check-up can diagnose early-stage cancers and this elevate survival rate by a lot, deaths could then be prevented. The person also will take more care in one's diet and health to prevent onset of the disease.
Although the rift between diagnosis and cure gradually widens more as disease prediction outpace medicine's ability to treat , in my opinion it is still better than not being able to diagnose at all. Moreover, looking back at the history, any cure to a disease starts from our ability to be able to diagnose it first. Without diagnosis and any knowledge on the particular disease, there would not be any cure.
Still, counseling and guidance are needed for those who undergo genetic testing. Every person has different perception on the result of the genetic test. Some may appreciate the information and strive to make their live better; others may suffer serious psychological impact and unstable family relations later on. So, counselors have a role to make sure the people who take genetic test is psychological prepared for any possibility of positive test result and help them adjust their life with the result later on.
Besides that, laws should be put in place to prevent discrimination against the affected person from being rejected getting their prospective job or denied their eligibly for insurance coverage. The test result also should be kept in confidential as leakage of information may seriously affect the life of the affected with the people and the society around them.
In conclusions, genetic testing shows a great potential to improve quality the life and health of human society, especially when the rift of diagnosis and cure close in gap. With further research and improvement in health science and technology, together with strong legislative and protocols to support it, genetic testing to diagnose and cure disease may bring about another medical revolution.