The Jiang lab in the Department of Pediatrics, Division of Medical Genetics at Duke University focuses on finding the genetic or the epigenetic basis of various mental disorders such as autism, Angelman syndrome and Prader-Willi syndrome. Each of the mental disorders has its unique genetic or epigenetic link and pathophysiology. However, interestingly, there is evidence that three seemingly unrelated mental disorders: autism, bipolar disorder and schizophrenia have a genetic overlap [Carrol et al. “Genetic overlap between autism, schizophrenia and bipolar disorder”. Genome Medicine 2009], possibly due to similar pathophysiology underlying these disorders. It would be interesting to identify these specific mutations and determine how these mutations affect protein structures that further affect neuron function. Then, targeted drug treatment could be developed, and these diseases, which are now considered almost incurable, might finally have a potential cure.
My project is a sub-project of this broader scheme. Specifically, I’m interested in looking at bipolar disorder. According to the National Institute of Mental Health, “bipolar disorder, also known as manic-depressive illness, is a brain disorder that causes unusual shifts in mood, energy, activity levels, and the ability to carry out day-to-day tasks.” As its name suggests, it is characterized by periodic mood swings between depression and mania. Surprisingly, bipolar disorder has seldom been as extensively studied as autism and schizophrenia, and almost no genetic mutations have been held responsible for causing the disease. So I’m interested in searching for candidate mutations that may have an effect on the structure of certain brain proteins and potentially cause the disease.
To accomplish this goal, I have genomic DNA samples from 96 bipolar human patients to start with. I’m trying to use PCR to amplify the portion of interest from the entire genome. Gel electrophoresis is then utilized to determine the purity of the PCR product. As simple as this may sound, the whole process is actually quite an effort because it is very hard to get a PCR product clean and pure enough to be sent directly for sequencing. So my current task is still mostly optimizing PCR (changing the amount of primers added, playing with the annealing temperature etc.) in order to get rid of nonspecific bands and minimize primer dimers, both of which interfere with sequencing. Once PCR is perfected, my work will involve more computational biology such as sequence alignment and comparison in order to search for any mutation that are common to these patients. This is the primary goal of my short-term project.
If there is any mutation that either causes a change in amino acid sequence (and therefore a change in protein structure), or introduces an early stop codon that blocks the expression of the protein, it is very likely that neuron functions, especially post-synaptic transmission will be impaired. So looking ahead, in the long run, if I indeed find any significant mutations, I will be looking at whether they are just common variants in the human species, and if the mutated sites are evolutionarily conserved. If they are not common variants and are indeed evolutionarily conserved (and therefore functionally relevant), that would be a huge deal. However, my short term project is a rather long shot, both because my sample size is very limited, and because the genetic cause of bipolar disorder has not been extensively studied. But this is exactly why I am very excited about this project: even if I end up finding nothing significant, I am still exploring something new, and this process itself is truly appealing.
