What is Personalized Medicine?

Traditional methods of medical practice apply the same treatment regimen for all individuals with the same disease despite the knowledge that there exists a difference between each patient’s genetic make-up and the influence of environmental factors. However, with the advent of genetic analysis technologies, treatments can be personalized to increase their effectiveness and safety. The field of personalized medicine is being used in several diseases with positive results, particularly within the field of oncology.

A novel field, currently under investigation, is personalized medicine within psychiatry.

Personalized Medicine and Predicting Susceptibility

One of the main applications of personalized medicine is the prediction of disease susceptibility using genome-wide association studies (GWAS). In these studies, genomes of patients with a certain disease or disorder are analyzed, identifying small variations within the genes called “single nucleotide polymorphisms” (SNPs). Common SNPs from healthy individuals and individuals with the diseased genomes are compared to help identify SNPs that is more frequent in a particular disease. SNPs that are more common in diseases are therefore genetically linked to the disease. Screening for individuals with linked SNPs can be used to indicate susceptibility to a specific disease, allowing for prescribing preventative medications and communicating the need for lifestyle changes and reducing the occurrence of disease.

Below are some examples of the disease areas where personalized medicines have forayed.

Major Depressive Disorder

Major depressive disorder or clinical depression affects an individual’s mood with symptoms including constant sadness, irritability, hopelessness, decreased energy, and sleeping problems. This condition has a strong association with heredity, with a genetic link of approximately 40-70%. Numerous linked SNPs have been identified to date, such as the tryptophan hydrolase gene, corticotropin-releasing hormone receptor 1 (CRHR1) gene, corticotropin-releasing hormone-binding protein (CRHBP) gene, and the variable number repeat region (VNTR) of the 5-hydroxytryptamine (serotonin) transporter (5-HTT) gene. The patients can be screened for these SNPs to check for genetic susceptibility thereby preventing this disorder even before it has started.

Schizophrenia

Schizophrenia is a chronic mental disorder that has numerous disabling symptoms including delusions, hallucinations, memory problems, and depression. This condition also has a very strong genetic link, between 50-80%. However, this condition is very complex, and the contribution of genetics has not been completely understood.
Despite this fact, there are a number of genetic variations that have been identified so far. These include SNPs within the zinc finger 804A (ZNF804A) gene, transcription factor 4 (TF4), and Neuregulin 1 (NRG1). Over 1000 genes and 8000 variations have been investigated but further research is required before SNP analysis can be routinely used in medical practice.

Bipolar Disorder

Bipolar disorder, or manic-depressive illness, is a severe mental disorder characterized by unusual shifts in moods and emotional status that effect the energy and activity levels. This disorder alternates between manic or depressive episodes. Typically, lithium is prescribed for patients with this condition that dramatically stabilizes their mood swings.

Investigations have revealed that specific genetic variations are associated with a beneficial response to lithium, such as SNPs within X-box binding protein 1 (XBP1), glycogen-synthase kinase 3 beta (GSK3B), and breakpoint cluster region (BCR). Therefore, doctors can make an informed judgment on how a patient will respond to a particular treatment regimen upon analysis of the patient’s genome.

Personalized Medicine and Predicting Treatment Response

Many genes, notably cytochrome P450 enzymes, are involved in the metabolism of drugs. Variation within these genes can alter the duration that drugs remain within the blood plasma, and therefore can affect the function of the drug. For example, overactive enzymes break down the drug too quickly, resulting in reduced therapeutic affect whereas inactive enzymes lead to a higher drug concentration resulting in possible overdose.

By analyzing an individual’s genome, dosage decisions can be guided and personalized, ensuring that each patient receives drug concentrations that are optimal to show the desired therapeutic effect. Such tailor-made medicines lead to increased efficiency, efficacy, and treatment safety.

The Future of Personalized Medicines in Psychiatry

Sustained research in personalized medicine is required to improve genetic testing for psychiatric conditions and to help identify SNPs that are involved in disease susceptibility. The knowledge database can be increased by including OMICS fields such as transcriptomics and proteomics. Another rapidly advancing area is neuroimaging genomics. Neuroimaging genomics can help improve the existing understanding of common psychiatric disorders by evaluating the imaging patterns of an illness that has a well-documented genetic make-up and the variations that happen when a specific change happens to the genome.

In the end, personalized medicine such as psychiatric pharmacogenomics may be the future of medicine, helping improve efficiency and safety of medical practice.

Reviewed by Deepthi Sathyajith, MPharm