Current thought is that while some HD patients have a single mutation that is sufficient to cause HD, many patients likely have weaker mutations in multiple HD susceptibility genes that together are sufficient to cause HD[8, 9]. While there has been intense study of the genetics of HD over many years, there has been no attention given to possible genetic etiologies of HAEC. To date, the influence of genotype on the HAEC phenotype has received little attention, thereby providing additional merit for this proposal.