The expanded and unstable CAG repeat tract at the 5' end of a novel 4p16.3 gene triggers the death of striatal neurons in Huntington's disease (HD). The process by which this genetic defect selectively kills is not known. Discovery of the HD mutation is a fundamental starting point for deciphering the steps that lead to the pathology of HD. Investigations into the behavior of the repeat and the repercussions of its expression all require knowledge of HD CAG repeat length. The major goal of the Genotyping Core is to provide investigators in the HD Center with an accurate estimate of the lengths of the HD CAG repeats carried by the normal and disease chromosomes in the cells and tissues that are being studied. The Core will perform DNA typing at other loci in the genome requested in efforts to identify genes that modify disease. The core will also provide additional services such as culturing of cells, the extraction of genomic DNA from cells and tissues, and routine DNA sequencing and typing of other polymorphic DNA markers from the vicinity of HD or at other locations in the genome.