Although mean plasma Abeta40 levels are elevated in sporadic AD and influenced by Apo E genotype, measurement of plasma Abeta40 levels is not useful to support the clinical diagnosis of AD. Lower levels of CSF Abeta42 in the AD group are consistent with previous studies.

We have evaluated 62 fragile X syndrome [fra(X)] individuals (55 males and 7 females) with different degrees of developmental disabilities that were clinically non-progressive and non-focal in character. The mean age for the 55 males was 23.1 years +/- 14.3 SD with a range of 2-70: for the 7 females, the mean age was 15.7 years +/- 3.5 SD with a range of 10-20 years. Mental retardation (MR) was found in 53 males (8/53 [15.1%] mild, 26/53 [49.1%] moderate, 14/53 [26.4%] severe, and 5/53 [9.4%] profound). Learning disabilities were found in 2/55 (3.6%) of males. One of the 7 females had mild and one had moderate MR: the other 5 were learning disabled. Autistic stigmata were present in 10/62 (16%) of the patients. Only 14/62 (23%) had a history of seizures, all of which were controlled with anticonvulsants. In 36/62 cases, an electroencephalogram (EEG) was performed. We compared these data with that of others. Brain stem auditory evoked response (BAER) was performed in 12 cases. Abnormalities were found in only 5/12. Neuroimaging and computerized cranial transaxial tomography (CT scan) were performed on 21/62 (34%) of the patients. Only 8 of these 21 (38%) studies were abnormal. One patient died; neuropathological studies showed mild brain atrophy, with light microscopic and ultrastructural abnormalities. Rapid Golgi dendritic spine patterns showed that the proximal apical segments were abnormally developed. Very thin, long tortuous spines with prominent terminal heads and irregular dilatations were present. Marked reductions in the length of the synapses, as determined on EPTA-postfixed tissue where noted.(ABSTRACT TRUNCATED AT 250 WORDS)

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The ubiquitous presence of the neuropathology of Alzheimer disease (AD) in individuals with Down's syndrome (DS) over 40 years of age suggests that this group of people will exhibit a high prevalence of dementia of the Alzheimer type (DAT) as they age. The present study indicates that there is a clear discrepancy between the presumed presence of AD neuropathology and the clinical expression of DAT among older people with DS. In the first 6 years of a longitudinal study, the present authors compared 91 adults (31-63 years of age) with DS and mild or moderate mental retardation to 64 adults (31-76 years of age) with other forms of mental retardation (MR) on yearly measures of mental status, short- and long-term memory, speeded psychomotor function, and visuospatial organization. The results indicated that, over repeated testing on the verbal long-term memory test, younger participants with DS showed small increases in their scores, while older participants with DS showed very slight decreases. Overall performance scores on this test and a speeded psychomotor task were poorer for both diagnostic groups in individuals aged 50 years and older. The magnitude and type of these selective changes in performance were consistent with performance profiles observed in older healthy adults without mental retardation on tests measuring similar cognitive functions. Only four out of the 91 people with DS in the present sample showed changes in functioning that have led to a diagnosis of possible DAT, and in these individuals, alternative causes of performance declines were concurrently present (e.g. thyroid dysfunction). These findings indicate that some age-associated changes in functioning are related to "normal' but probably precocious ageing among adults with DS. Furthermore, these findings suggest that adults with DS and mild or moderate mental retardation may be at lower risk for dementia during their fourth and fifth decades of life than previous studies have suggested.

Several inbred strains of mice were injected with different scrapie agents and their total body weight was monitored throughout the incubation period. As a control, mice were injected with normal mouse brain homogenate. For most combinations of scrapie agent and mouse strain, weights during the preclinical phase were similar to or lower than the average weight of controls. For some combinations there was a significant increase in weight (compared to controls) during the latter part of the preclinical phase of disease. The effect was dependent on both agent and mouse strain, i. e., in some cases a mouse strain showed the increase with one scrapie agent but not another and some scrapie agents caused the increase in one inbred strain of mouse but not in another strain. The increase in weight was due to accumulations of fat rather than a generalized increase in weight of various organs. With one mouse strain (SJL), there was increased vacuolation seen in the hypothalamus of mice injected with scrapie agents that showed the increase in weight compared to the lesion intensity with an agent which did not cause the weight increase.