No abstract

A small number (1-5%) of Alzheimer's disease (AD) cases associated with the early-onset form of the disease (EOAD) appears to be transmitted as a pure genetic, autosomal dominant trait. To date, three genes responsible for familial EOAD have been identified in the human genome: amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2). Mutations in these genes account for a significant fraction (18 to 50%) of familial cases of early onset AD. The mutations affect APP processing causing increased production of the toxic Abeta42 peptide. According to the "amyloid cascade hypothesis", aggregation of the Abeta42 peptide in brain is a primary event in AD pathogenesis. In our study of twenty AD patients with a positive family history of dementia, 15% (3 of 20) of the cases could be explained by coding sequence mutations in the PS1 gene. Although a frequency of PS1 mutations is less than 2% in the whole population of AD patients, their detection has a significant diagnostic value for both genetic counseling and treatment in families with AD.

A b s t r a c t Alzheimer disease (AD) is a complex, multi-factorial disease with the potential involvement of several genes. Alpha-2-macroglobulin (A2M) has been implicated in AD on the basis of its ability to mediate the clearance and degradation of β-amyloid peptide. Nevertheless, it is not clear whether there are racial differences in frequency of polymorphisms of A2M in AD. We examined a group of 50 unrelated patients from Poland (38 women and 12 men), who were diagnosed clinically as probably developing AD (according to the N1NCD3 -ADR PA criteria). The patients were examined by a neurologist and a psychologist and had a CT or MRI scan of the brain. Fifty individuals of matched age, withoutany signs of dementia, were studied as a control group. DNA was extracted by a routine method from a blood sample. Amplification and genotyping at A2M was performed as described by Blacker et al. (1997). The genotypic distribution in A2M exon 18 in patients with AD and genotype TT in A2M exon 24 was similar to that in the controls. Significant differences were noted only in early onset AD in males and for old onset disease in females. The deletions were found more frequently in AD; however, they were found in only a small proportion of studied patients. These findings indicate that A2M is not the only biological candidate gene for AD determination.