New Cell Lines for Huntington's Disease
Huntington's disease (HD) is a devastating neurodegenerative disease with a 1/10,000 disease risk that always leads to death. These numbers do not fully reflect the large societal and familial cost of HD, which requires extensive caregiving and has a 50% chance of passing the mutation to the next generation. Current treatments treat some symptoms but do not change the course of disease. Symptoms of the disease include movement abnormalities, inability to perform daily tasks and and psychiatric problems. A loss os specific regions of the brain are observed. The mutation for HD is an expansion of a region of repeated DNA in the HD gene and the longer the repeat, in general the earlier the onset of disease. While the length of this polyglutamine repeat largely determines the age-of-onset, there is variance in onset age that is not accounted for by repeat length but is determined by genetic and environmental factors. In addition, the symptoms can vary significantly among patients in a non-repeat dependent manner. To assist in preventing onset of HD, there is a great need to identify genes that are involved in why one individual with 45 repeats will manifest symptoms at age 40 while another manifests symptoms at age 70. Further, there is a lack of early readouts to determine when to begin HD treatments. Because the disease mutation is known, preimplantation genetic diagnosis (PGD) is possible and mutant Htt embryos are available. Stem cell lines can be derived from PGD embryos with varying repeat lengths and genetic backgrounds to provide new methods to identify genetic modifiers and readouts of disease progression. The development of pluripotent stem cells, termed induced pluripotent stem cells (iPS) cells, derived directly from HD patient fibroblasts, would also provide new methods for these analyses. Chemical compound screens to identify drugs that protect against the effect of mutant Htt protein expression in patient derived hESCs cells would allow evaluation of drug responses in on cells having different genetic backgrounds Ultimately, the iPS cells can provide a way to transplant neurons or neuronal support cells from affected individuals or from unaffected family members having a normal range repeat. Such cells would help reduce immune rejection effects likely to occur with transplantation, however, while patient-derived cells overcome the problems of immune rejection, the mutant protein is still expressed. To overcome this problem we will genetically modify these stem cells to reduce the mutant protein and produce a normal gene. Beyond the immediate application to HD, the development of these models is applicable to a range of neurodegenerative diseases including Alzheimer's and Parkinson's diseases.
Leslie Michels Thompson
University of California, Irvine
New Cell Lines