Presumed Alzheimer's disease beginning at different ages in two twins

Monozygotic twins concordant for late-onset probable Alzheimer disease with suspected Alzheimer disease in four sibs

Probable Alzheimer disease (AD) is described in 79-year-old male twins with monozygosity confirmed by DNA examination. The first twin to be affected began to show signs of intellectual deterioration at age 70. In the other, onset was at age 72. Four of their living sibs (current age range = 75-92) are also suspected to have AD. The possible roles of genetic and environmental factors in the development of AD in this sibship are discussed.

Familial Alzheimer's disease: progress and problems

This paper reexamines recent epidemiologic and molecular genetic studies on the genetic basis of Alzheimer's Disease (AD). Careful analysis of the available epidemiologic data strongly suggests that at least a proportion of AD results from the inheritance of an autosomal dominant gene defect. However, studies of isolated families, of concordance rates in twins, and of risk for AD in relatives of AD probands yield conflicting data. While it is likely that much of the conflict can be ascribed to methodologic differences, it remains premature to conclude that all AD is transmitted as an autosomal dominant trait. Molecular genetic techniques hold the promise of isolation and characterization of the genetic defect(s) in familial AD (FAD). Recently, chromosome 21 has been implicated as the potential site of an autosomal dominant defect in some but not necessarily all FAD pedigrees. However, the results of recent genetic epidemiologic studies suggest that progress in the molecular genetic approach to AD will be difficult.

Genetics, Alzheimer's disease and senile dementia

Genetic factors in the aetiology of Alzheimer's disease (AD), are now being intensively investigated. The homogeneity of AD is under investigation. There are a few large kindreds with early onset of AD in whom transmission appears to be typically autosomal dominant, and 65% or more of the remaining cases at any age may have genetic aetiology. Both multifactorial and autosomal dominant inheritance with age-dependent expression have been proposed, but the late onset and death of unaffected relatives from competing causes make it difficult to choose between them. Lifetime risk gives the best estimate of incidence in family studies, but clinical and pathological criteria are not clear enough for confident diagnosis of AD in late old age. A role for external factors is indicated by twin studies, and the role of aluminium is currently under investigation. Molecular genetics promises to resolve many questions. The clinicians' role will be to provide well documented families for interdisciplinary research and to help in clarifying diagnosis in late old age.

Cerebral metabolism, anatomy, and cognition in monozygotic twins discordant for dementia of the Alzheimer type

One pair of monozygotic twins discordant for dementia of the Alzheimer type (DAT) was studied using neuropsychological testing, quantitative x-ray computed tomography (QCT) and magnetic resonance imaging (MRI) of the brain. Cerebral glucose metabolism was measured using positron emission tomography (PET) and 2-[18-F]fluoro-2-deoxy-D-glucose (FDG). The affected twin had a seven year history of progressive cognitive impairment and was severely demented. Neuropsychological testing of the affected twin demonstrated marked deficits in all areas of cognitive function. The asymptomatic twin showed some impairment on tests of perceptual organisation and delayed recall. The affected twin had loss of gray matter and ventricular enlargement on QCT and MRI compared with healthy controls (p less than 0.05). He also had frontal and parietal lobe hypometabolism and increased asymmetry of metabolism on PET compared to both his twin and healthy age-matched controls (p less than 0.05). PET, QCT, and MRI distinguished changes in the twin with DAT compared with his brother and healthy controls. Although the subtle neuropsychological abnormalities of the asymptomatic twin may be signs of early DAT, they were not accompanied by any changes in regional cerebral metabolism or brain structure.

The genetics of Alzheimer's disease: a review and a discussion of the implications

This paper examines the evidence for a genetic etiology of Alzheimer's Disease. Three groups of cases are identified; the first being those with a consistently early age of onset, in which autosomal dominant inheritance can be established. These families may require genetic counseling, and represent an extraordinary resource for research. There are early onset cases without a strong genetic component, and later onset cases generally show only weak evidence of hereditary disease. Some of the apparent distinctions between these groups may result from methodologic problems, especially if the age of onset of symptoms is highly variable in the majority of families. Studies of associations between Alzheimer's Disease and Down's Syndrome suggest a role for genes on chromosome 21 in the genesis of the pathologic features, and testable hypotheses can be identified. Attempts to link the development of Alzheimer's Disease to the presence of specific inherited markers have generally been unsuccessful to date, but there are some promising findings. Recent progress in understanding the molecular basis of other inherited diseases is reviewed in relation to attempts to understand the possible molecular basis of Alzheimer's Disease. A limiting factor in future studies will probably be the availability of cells and tissues from pedigrees demonstrating autosomal dominant inheritance of this disorder.