The uptake of predictive testing for Huntington disease informs our understanding of decision making by those at risk and assists with planning for service provision. Uptake figures have been reported from several centers based on the total number of people who have undertaken predictive testing as a percentage of those estimated to be at 50% risk in the region. This method produced a figure of 35% from our own service, much higher than observation of the local pedigrees indicated, and higher than other published reports. We have identified some errors in the commonly used formula. The major errors are the use of the cumulative total of those who have had testing with a static denominator of those at 50% risk, and the failure to exclude from the at-risk group those who are too young and therefore ineligible to test.We report data from the Huntington Disease Register of Victoria and estimate the prevalence to be 8 per 100,000 in 1999. Additional data on individuals at risk were collated. We found that for every diagnosed person there were 4.2 individuals at 50% risk, a lower ratio than one to five hypothesized in the literature. We examined these ratios in the context of uptake.Significantly, we provide a solution to the calculation of uptake with a formula that factors in a dynamic denominator and corrects for the number of years testing has been offered. Using this formula, we calculated an uptake of 13.0-15.4% for the state of Victoria, Australia. This formula can be used to compare uptake across different centers.

Huntington's disease (HD) is an autosomal dominant disorder, involving the gradual degeneration of specific regions of the nervous system. One of the aims of genetic counselling is to provide factual information concerning the nature of the condition for subjects suffering from or at risk for HD.The task of the genetic counsellor may be facilitated by factual information concerning the general socioeconomic characteristics of the population with which he is working. The aim of the present study was to increase systematic knowledge concerning selected characteristics of those people in Victoria, Australia who have a 50% chance of inheriting HD. The socioeconomic characteristics of our population, such as education, occupation, marital status, and number of children, has not been previously studied and it was thought that knowledge of such variables could be useful in analysing socially relevant issues.The level of knowledge of this population concerning the genetics, progress, and treatment of HD is also of interest in determining the effectiveness of genetic counselling programmes previously carried

Summary. In an attempt to relate the age at onset of Huntington's disease to parental factors, the effects ofparental onset-age (P.) and the age ofthe transmitting parent at the birth of a subsequently affected child (P,) Such an approach would be useful for counselling subjects at risk by providing a more accurate probability of inheritance than is now possible.

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