A Common Theme
Quick: what do bipolar disorder, schizophrenia, depression, autism, and attention-deficient hyper-activity disorder all have in common? A portion of each of them can be attributed to the same genetic mutations (Cross-Disorder Group of the Psychiatric Genomics Consortium, 2014). It is not at all surprising that psychiatric disorders can be inherited. What is eye-opening is that the same genetic mutation is implicated in more than one mental illness.
Traits are inherited from parents. These include characteristics like blue eyes, nose shape, or depression. The study of how this inheritance takes place is called genetics.
Sometimes it is easy to figure out how a trait is inherited with genetics. Other times it is complex. DNA (deoxyribonucleic acid) is the name of the molecule within each cell of our body that contains the blue print, making each person unique. Half of each person’s DNA comes from their mother and half from their father. A unit of DNA that makes a specific part of the cell (a protein) is called a gene.
Traits for which genetic inheritance is simple are controlled by one gene. More complicated traits are controlled by two to three genes. Sometimes there are many genes that control a complex trait such as height.
DNA is composed of four chemicals called Adenine, Cytosine, Guanine, and Thymidine. These are abbreviated A, C, G, T. They are strung together like beads in a specific order. The entirety of the DNA in one organism is called a genome. The human genome is composed of 3.2 billion of A’s, C’c, G’s, and T’s.
Genes within a genome contain “typos” or mutations in the DNA. The result of these mutations can be completely innocuously to lethal (Wikipedia Genetics, 2014).
Today, scientist can study genetics by sequencing the entire genome in a person. Sequencing refers to the determination of the exact order of A’s, C’s, G’s, and T’s. The first complete human genome was sequenced in 2002 at a cost of $3 billion dollars took over 13 years. Currently, a person’s genome can be sequenced for less than $1000 and can be done in one week. What takes more time and money is the interpretation of the sequenced genome (Wikipedia Human Genome Project, 2014).
For many years, scientists, doctors, and patients have hoped that by looking at the complete genome a patient, the precise reason for a disease could be pinpointed. Treatment could then be tailored precisely for that individual. This is the concept of personalized medicine.
Cancer treatments, especially ones for breast and blood cancers, have greatly benefitted from this idea. To determine the best course of treatment in these cancers, the entire genome does not need to be sequenced. The sequence of only a few genes needs to be determined to find the best course of treatment (Wikipedia Personalized Medicine, 2014).
Genome Sequencing Applied to Mental Illness
Determination of mental health disorders with personalized medicine is in its infancy. A striking example can be found in relatives of actress Glenn Close. Her sister, Jessie, and nephew, Calen, both suffer from mental illness. Jessie is bi-polar, while Calen is schizophrenic. Researchers found that they both have the same genetic mutation resulting in a lack of glycine. When Jessie and Calen were treated with a medication to remedy the problem, their symptoms were greatly alleviated (Stessman, Bernier & Eichler 2014 and Insel 2014)
It is unsurprising that Jessie and Calen shared the same genetic mutation. Nor is it interesting that they had different diagnoses of mental disorders (bipolar vs. schizophrenia). Shockingly, they both benefited from the same medication to treat the mutation they both carry (Stessman, et al., 2014).
With genetic screening, one day psychiatrists will be able to prescribe medication based on the results of genetics screening. Determining the best medication quickly will be a much more efficient way of treating mental illness than the current, try-this-medication-and-see-if-it-works approach. Effective medication will be more easily determined from genomic sequencing, but diagnosis of complex diseases will also become possible (Cross-Disorder Group of the Psychiatric Genomics Consortium, 2014).
The story of Jessie and Calen may seem to be the Holy Grail in the search for understanding the genetic component of mental illness. But it is only another piece in a very large puzzle.
Cross-Disorder Group of the Psychiatric Genomics Consortium. (2013). Genetic relationship between five psychiatric disorders estimated from genome-wide SNPs. Nature Genetics, 45, 984–994.
Insel T. (2014). Director’s Blog: Celebrating Science. Retrieved on May 18, 2014 from http://www.nimh.nih.gov/about/director/2014/celebrating-science.shtml#1
Stessman H. A., Bernier R., Eichler E. E. (2014). A genotype-first approach to defining the subtypes of a complex disease. Cell, 156 (5), 872-7.
Wikipedia Genetics. (2014). Retrieved on May 19, 2014 from http://en.wikipedia.org/wiki/Genetics
Wikipedia Human Genome Project. (2014). Retrieved on May 19, 2014 from http://en.wikipedia.org/wiki/Human_Genome_Project
Wikipedia Personalized Medicine. (2014). Retrieved on May 19, 2014 from http://en.wikipedia.org/wiki/Personalized_medicine