Clinical genetics and genetic counseling in Alzheimer disease

Article Abstract:

Alzheimer disease is a syndrome of progressive deterioration, characterized by memory loss and loss of ability to perform the activities of daily living. Two forms of the disease are recognized. One form typically begins in middle age and appears to have a familial tendency. The other, more common type starts in the later years, and has not traditionally been thought to have familial clusterings. Recently, some authorities have suggested that the later form also has an inherited tendency, although it is not as strong as that of the early-onset form. Genetic studies have shown that certain chromosomal abnormalities are common to many Alzheimer patients. First-degree relatives (siblings and children) of those with Alzheimer disease have a 20 to 25 percent chance of developing the disease themselves, and Alzheimer disease is inherited in what appears to be an autosomal dominant pattern, meaning that there is no difference between the risk for each sex. Because death from other causes may be eliminating some people from studies of late-onset Alzheimer disease before they would have developed symptoms, the risk of developing Alzheimer disease may be even higher than 20 percent. The fact that one identical twin might develop Alzheimer disease while the other does not suggests that environmental factors may influence the inherited tendency toward the development of the disease. A new drug therapy is being developed to counter the symptoms of Alzheimer disease. These drugs should probably be offered to those relatives of Alzheimer patients considered to be at high risk for getting the disease themselves. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Evidence for allelic heterogeneity in familial early-onset Alzheimer's disease

Article Abstract:

Studies of early-onset Alzheimer's disease in families have found evidence for the involvement of chromosome 21. Age of onset varies between families, but within families several studies have indicated that members who show symptoms of Alzheimer's disease tend to do so at about the same age. The reason for the variation between families is not clear; this may also simply be a selection bias in the experimental protocols used. To further examine family-specific age of onset, 30 families with evidence of familial early-onset Alzheimer's disease were examined with regard to age of onset of memory loss or behavior change. There were a total of 214 affected individuals and of these age of onset information of symptoms was available for 139. Analysis showed that 77 percent of the differences in age of onset were accounted for between families, rather than within families. That is to say, age of onset varied very little within families versus between families. This held true even for seventh- and eighth-degree relatives who had only a small percentage of genes in common, suggesting that age of onset is genetically controlled within the family gene pool and is determined by old genes in the family history. Implications include the possibility that individuals whose age of onset differs from the other family members can be identified and studied with regard to other causative factors, as they may not have inherited their illness. Other implications are discussed. (Consumer Summary produced by Reliance Medical Information, Inc.)

Research, Dementia, Allelomorphism, Alleles

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Is parental age related to the risk of Alzheimer's disease?

Article Abstract:

Research has demonstrated a genetic link between Alzheimer's disease (AD) and a defect on chromosome 21, which is the same chromosome implicated in Down's syndrome. Since increased maternal age is a significant risk factor for Down's syndrome, there has been an interest in evaluating connections between parental age and risk for AD. However, studies evaluating the relationships between parental age and risk for AD have yielded inconsistent results. To further evaluate the possibility of such a relationship, the ages of the parents of 198 male and female AD patients were compared with the parental ages of 198 healthy men and women randomly selected from municipal population registers, and matched for age and gender. An AD diagnosis was made only if patients demonstrated a slow, progressive decline in intellectual function, specific cut-off scores on several mental status and dementia scales, and no evidence of brain abnormalities other than cerebral atrophy (wasting or shrinkage). No relationship was found between maternal or paternal age at the time of the patient's birth and risk for developing AD. In fact, the average age of parents of the AD patients in this study was slightly lower than that of parents of the healthy men and women. (Consumer Summary produced by Reliance Medical Information, Inc.)

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