Risks of manifestation of Huntington chorea

A methodology allowing the estimate of risks heterozygosity and manifestation of Huntington's chorea (HC) within preestablished periods for individuals of any age was developed. For this, the procedure was the following: 1. The variables which could influence the distribution of age frequencies were studied. 2. The error due to the exclusion of the heterozygotes dying before the manifestation of the disease from the distribution of Wendt et al. (1959) of affected persons was corrected separately for each sex. 3. The frequency of non-affected heterozygotes in each age group was calculated separately for each sex, from the corrected distribution. From those data estimates of the following parameters could be reached: a) the probability of heterozygosity for consultants of any age; b) the risks of manifestation for the gene in a given individual within a determined period, taking into account his probability of heterozygosity and survival. 4. The risks of manifestation were tabulated for making easier their use in concrete cases. Simplified tables with approximate risks are also presented for the more common cases in genetic counseling. 5. The methodology presented allows a discrimination between the probability of heterozygostiy and the risk of manifestation. This makes possible the estimate of risks of becoming affected, taking into account not only the age of the consultant at the moment, but also the period of time starting with the consultation, to which the risk applies. This is essential for adequate genetic counseling.