Cognitive function and prediction of dementia in old age

Cognitive performance in relatives of patients with probable Alzheimer disease: an age at onset effect?

Cognitive performance of 32 siblings and children of patients with probable Alzheimer disease was assessed longitudinally over an interval averaging 4 years. Mean scores were within normal limits for age on all measures at both test times. However, relatives of patients with early-onset dementia (less than or equal to 67 years) were more likely to show a decline in performance from the first to second testing than relatives of patients with late-onset dementia. Additional follow-up will be needed to determine the reliability of performance trajectories and to assess whether mild cognitive changes are related to future dementia. However, findings suggest that it may be important to consider family history of dementia in studies of normal cognitive aging.

Commingling analysis of memory performance in offspring of Alzheimer patients

Dementia of the Alzheimer type (DAT) is a neurodegenerative disorder which afflicts approximately 3% of the population. Genetic influences are indicated from twin and family studies although genetic heterogeneity has been suggested from both pedigree analyses and linkage investigations. Autosomal dominant inheritance with age-dependent penetrance has been suggested in at least some families with DAT. In the present investigation, we examine memory and nonmemory task performance in 106 asymptomatic offspring (mean age 40.6 years) of 54 DAT probands. Intraclass sibling correlations revealed little evidence of sibling similarity for performance on three memory tasks which have been reported to be relatively sensitive to the memory losses accompanying DAT. Subsequent investigations of the distributions of the cognitive task scores in the offspring revealed evidence for a commingling of two distributions for the three memory tasks but not for the nonmemory measures. These findings are consistent with a hypothesis that these distributions reflect genotypic subgroups, carriers, and noncarriers, of a presumed DAT gene.

The validity of the diagnosis of mild dementia

Five operational methods for clinical diagnosis of mild dementia were compared to find out their diagnostic concordance when applied to a single group of seventy-five subjects. The clinical validity of the diagnoses was assessed in terms of their capacity to predict continued cognitive deterioration over three years after diagnosis and their capacity to reject the diagnostic influence of 'non-dementia' factors (that is, the cognitive consequences of depression, poor intellect, limited education and non-neurological physical illness). By all criteria of clinical validity the diagnostic methods for mild dementia performed poorly. Kappas measuring agreement between methods averaged only 0.15 and up to 57% of diagnostic deviance was explained by 'non-dementia' factors. Prediction of continued deterioration was poor, with a false positive rate which was too high for the diagnoses to be clinically usable. By no criterion of validity did the diagnostic methods exceed the performance of a clinician's judgement of the presence of pathological cognitive impairment or diagnosis by a cutpoint on the Mini-Mental State Examination.