Predictive Testing for Huntington's Disease: How Does it Impact on Cognitive Performance?

Abstract

The discovery of a polymorphic DNA marker for Huntington's Disease (HD) in 1983, and the specific gene responsible in 1993, led to predictive testing programmes out of which came research into whether or not cognitive impairment was present presymptomatically in those at risk for HD. The results of these studies have been conflicting and inconclusive. Methodoiogical limitations have probably contributed to the differing findings. The present study attempted to expand upon previous studies by analysing the data in a more comprehensive manner, and with additional control conditions. In this study, 26 individuals, at risk but presymptomatic, for HD were recruited from the Johannesburg Predictive Testing Programme and administered a battery of psychological tests prior to molecular analysis. Of this HD group, 11 were subsequently positive for the gene (the HD+ group) and 15 were negative (HD- group). A carefully chosen control group, (matched for age, sex, and education - Control Group 1) and a group of individuals experiencing a life threatening medical illness (without CNS involvement - Control Group 2) were administered the same battery of psychological tests. Four-way Analysis of Variance between the HD+, HD-, and Control groups was conducted to detect specific differences between the groups. The results indicated that the HD+ group showed mild impairment for declarative memory function. However, it would appear that undergoing the psychological evaluation itself impacted upon the test performance of both the HD+ and HD- groups.