We all differ from one another in many ways like what we eat, exposure to environment , genomic DNA etc. Most of these variations play a key role in health and disease e.g., the natural variations found in our genes could influence our risk of developing a certain disease, as well as how our body respond to that disease. These variations can affect each individual's susceptibility to a disease or reacting to something in the environment, and can be a reasons why a drug works for one patient and not for other.

Generally a physician gives the same medicine for a disease to a group of people suffering from that disease. But it is seen out of that group of individuals only few could recover and each of them respond differently to that medicine. This shows that there is something different in these individuals which made them to respond differently. What's the difference????

This difference lies in the GENOME of an organism. This is due to the genetic variation or the difference in the genome sequence of the individual. These genetic variations can be in a form of single nuceiotide polymorphism (SNP), insertions & deletions of sequences in the genome. The sequences of the genome are available after the success of different whole genome sequencing project ; one of the most important being the Human Genome Project.

The Human Genome Project (HGP) is an international scientific research project with a goal of determining the sequence of base pairs which make up our DNA and to identify approximately 20,000-25,000 genes of the human .The Human Genome Project (HGP) was a 13-year project which began in 1990 & completed in 2003.

Personalized medicine : The concept
Personalized Medicine is the concept which involves managing a patient's health based on the individual patient's specific characteristics, including age, gender, height/weight, diet, environment, etc. The concept of personalized medicine can be seen as an outcome of human genome project (HGP). Understanding what human traits the genes determine and the alterations that may cause human disease or medical problems helps the researchers to determine the forms of treatment or therapies that can be tailored to a specific individual, thus, the development of personalized medicine.

The various fields of research termed "-omics" that are genomics, proteomics, and metabolomics, study the contribution of genes, proteins, and metabolic pathways to human physiology and variations of these pathways that can lead to disease susceptibility. These can enable new approaches to diagnosis, drug development, and individualized therapy. Personalized medicine is basically aimed at tailoring drug therapy at a dosage that is most appropriate for an individual patient, with the potential benefits of increasing the efficacy and safety of medications with least side-effects. It is actually a gene-centered approach which may speed the development of novel therapeutics. It selects the most appropriate therapy for a disease or condition that is particularly suited to that patient according to his/her genetic make-up.

Difference in the genetic code between the people is the foundation of Pharmacogenetics
Pharmacogenetics (also termed as pharmacogenomics)
is the field of study that examines the impact of genetic variation on the response to medications. It is the branch of pharmacology which deals with the influence of genetic variation on drug response in patients by correlating gene expression or single-nucleotide polymorphisms (SNPs) with a drug's efficacy or toxicity. It is the science of how an individual's genotype affects their body's response to drugs. It also examines the impact of genetic variation on the response to medications as each individual response to a particular drug differently.

Personalized Medicine Vs Traditional Medicine
The traditional medicine approaches are generalized across human beings .e.g. when someone has symptoms of diabetes, these are symptoms that any human with diabetes might have, such as elevated blood sugar levels. Treatment is then determined by the knowledge developed by research on an entire population of people with the same blood sugar level problems.
On the other hand, Personalized medicine takes a person's genetic code into account when determining how to treat the medical problem that person is suffering from. e.g In the case of someone with diabetes, any treatment that a specific patient would receive would be based on a combination of diabetes genetic code findings ,generalized knowledge about blood sugar levels, the function of the patient's pancreas etc.
But this is only a concept. Genetically-based i.e. personalized diabetes treatments are not yet a reality.

How Does Personalized Medicine Work?
Personalized medicine is used in two aspects of human medicine: genetic testing for potential abnormalities and then tailoring treatment.

The Human Genome Project determine what genes exist in human DNA and what is their role in a healthy human being. This knowledge of genes and their behaviour when these occur normally can be compared with the genes of patients with medical problems to determine whether the patients' genes are abnormal. In some cases, a patient is tested when he or she begins to develop symptoms. Otherwise, genetic testing is generally done prior to development of symptoms.

Once tests are developed to determine abnormalities in human genes, then treatments or therapies can be developed accordingly. Then these treatments will be personalized to all human beings with the same genetic abnormality. The gene test results and environmental evidence can be considered for each person who needs treatment.

Breast cancer is one disease that is being treated based on genetic information. There are number of genes that have been found associated with breast cancer ,so the treatment decision can be made based on the knowledge revealed by the genetic testing. For example, women who have inherited the breast cancer genes will have a high risk of developing breast cancer, ovarian cancer or other female cancers. Therefore, they may choose to have surgical intervention before they actually develop these cancers.

Conclusion :

Personalized medicine is on the edge to transform healthcare over the next several decades. New diagnostic and prognostic tools will increase our ability to predict the outcomes of drug therapy. Early warnings about the disease can promote healthy lifestyles and can change the way treatments are discovered and used.

On the other hand , personalized medicine has to deal with various ethical & public issues like medical records privacy and clinical trial ethics etc. It can even raise certain questions like 'Is it beneficial to be informed that you are at high risk to develop a disease for which there is no cure??'

The way such issues are managed will affect the evolution of personalized medicine and its ability to prevent, diagnose and manage diseases effectively.

About Author / Additional Info:
I am a Mtech student from Delhi College of Engineering (DCE),Delhi...providing you a brief knowledge about the concept of a new class of medicine ,known as personalized medicine