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Before the mutation causing Huntington disease was identified, predictive testing of 25% at-risk persons with a 50% at-risk parent who did not wish to know his/her genetic status, was only possible by exclusion testing. The exclusion test, using linked markers, ensures the parent's wish not to know because the parent's risk is not changed. When mutation analysis became available in 1993, new testing options for 25% at-risk persons emerged: viz., the exclusion-definitive test and direct mutation analysis. These new tests not only disclose the risk of the test candidate, but may also change the risk of the at-risk parent and siblings. The testing options for 25% at-risk test applicants and their consequences are discussed and the testing procedures and results of testing 64 25% at-risk persons in the period 1987 to 1997 are described. Relatives received unsought information in 56% of the test procedures before and 34% after the mutation was identified. A decision tree and guidelines for predictive testing of 25% at-risk test applicants are proposed. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:662-668, 1999., (Copyright 1999 Wiley-Liss, Inc.)

Unlabelled: In the Dutch presymptomatic DNA-testing program for Huntington disease (HD), 29 individuals with increased risk and 44 with decreased risk were followed-up 6 months after test results. A prognostic model was built aimed at identifying individuals at risk for psychological maladjustment, as measured by the Impact of Event Scale, the Beck Hopelessness Scale, the General Health Questionnaire, and the Social Support Questionnaire., Results: 1) The more that applicants suffered from intrusive feelings about HD and tried to avoid HD-related situations, prior to the test, the greater the chance that they will experience this 6 months after the test if they proved to be at increased risk; 2) the more that both individuals with increased risk and those with decreased risk who suffered from the threat of having HD tried to avoid HD-related situations prior to the test and the less satisfied they were with available support, the greater the probability that they will show avoidance behavior after the test; 3) the more pessimistic that individuals with increased risk as well as those with decreased risk were about their future prior to the test, the more they avoided HD-related situations and the more dissatisfied they were about their available support (pretest), the greater the probability that they will become depressive and suicidal. Psychological adjustment was also studied as a function of a) intrusion/denial-avoidance pattern over time and b) healthy mental functioning/future expectancies. Most individuals with increased risk (86%) seem to cope well thus far, although this was based largely on strong psychological defenses and dependent on satisfactory relationships.(ABSTRACT TRUNCATED AT 250 WORDS)