Determining the mechanisms of nigro-striatal dysfunction in SGCE mutation positive Myoclonus Dystonia using an iPSC-derived neuronal cell model

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Aims1. To develop individual nerve cell models of Myoclonus Dystonia using skin cells (fibroblasts) from patients2. Detailed study of the nerve cell models to determine what effect SGCE gene mutations have on the cells, in particular the neurotransmitter (chemical allowing communication between nerves) dopamine and its receptors.Background to the research and its importanceDystonia is one of the most common movement disorders, affecting 1 in 900 per population head. Well recognised forms include writer's cramp, although more severe forms are frequently observed. Dystonia is associated with significant lifetime disability, which has an impact on education and employment. There are currently no effective treatments for dystonia, necessitating an improved understanding of the underlying disease causing mechanisms in order to allow development of novel and potentially disease-modifying therapies to be developed.This project is focused on Myoclonus Dystonia, an inherited, childhood-onset movement disorder with significant associated psychiatric symptoms. It is one of the most common forms of inherited dystonia and one of the few subtypes caused by mutations to a specific gene (SGCE). These characteristics make Myoclonus Dystonia an opportune disorder in which to study the underlying mechanisms of dystonia. The SGCE gene encodes the epsilon-sarcoglycan protein whose role in the brain, and how defects in its function give rise to dystonia, remain uncertain. Evidence from human brain imaging studies and animal models indicate that the communication (synapse) between dopaminergic neurons arising in the midbrain and medium spiny neurons in the striatum form a focal point of the neuronal disruption in dystonia.My previous research work involved recruiting one of the largest worldwide cohorts of patients with Myoclonus Dystonia. All of these patients underwent detailed examination of their movement disorder and any psychiatric symptoms. I have selected fibroblast samples from two patients (with different gene mutations) in order to generate these nerve cell models.Design and methodsThe fibroblasts will be used to generate induced pluripotent stem cell (iPSc), cells that are capable of developing into all tissue types. Using a series of well-established techniques, these cells will be converted into nerve cells, more specifically dopaminergic nerve cells (from the midbrain) and medium spiny nerve cells (in the striatum), two nerve cell types thought to be important in dystonia. Both nerve cell types will be examined to determine the effect of SGCE mutations on the epsilon-sarcoglycan protein. Detailed study will also be carried out of the enzymes involved in producing dopamine, the proteins involved in the transporting it across the cell membrane, and the receptors that signal its effect between the two cell types. The second stage of experiments will involve culturing both cell types together, examining their electrical communication and the structure of the neuronal processes. Results will be compared to nerve models produced from tissue donated by healthy, unrelated individuals. We also plan to use a new genetic technique (Clustered Regularly Interspersed Short Palindromic Repeats (CRISPR)) to 'edit' the cells from the patients with Myoclonus Dystonia, returning the SGCE gene sequence to normal, in order to demonstrate that the changes seen in the original nerve cell model are due to the SGCE mutations.Detailing these processes will improve our understanding of why dystonia, and potentially some psychiatric symptoms arise, as well as providing a platform for the development of new drugs and therapeutic options.