ABSTRACT
The beta-amyloid precursor protein (APP) gene (on chromosome 21), Presenilin 1 (PS1) gene (on chromosome 14) and Presenilin 2 (PS2) gene (on chromosome 1) are responsible for autosomal dominant early-onset Alzheimer's disease (EOAD). Missense mutations in these genes cause abnormal APP processing with subsequent overproduction of amyloidogenic and toxic A beta (42 peptide. A mutational analysis of APP, PS1, and PS2 genes can be used for both symptomatic and presymptomatic genetic testing and counselling in familial Alzheimer's disease (FAD). To contribute to our knowledge on genetic background of Alzheimer's disease in Poland, we screened APP mutations in a sample of familial EOAD cases from Poznan region. We did not find pathogenic mutations within exons 16 and 17 of the APP gene. Our study confirmed that APP gene mutations account only for a very small portion of FAD.
Subject(s)
Alzheimer Disease/genetics , Amyloid beta-Protein Precursor/genetics , Exons/genetics , Mutation, Missense/genetics , Adult , Aged , Amino Acid Sequence , Base Sequence , Female , Humans , Male , Middle Aged , Molecular Sequence Data , PedigreeABSTRACT
Mutations in Presenilin 1 (PS1) and Presenilin 2 (PS2) genes account for up to 50% of familial early-onset Alzheimer's disease (EOAD). In order to assess the genetic contribution of the PS genes in a series of Polish patients, we performed a mutational analysis in 6 autosomal dominant (ADEOAD), 8 familial and 41 sporadic EOAD cases from Poznan region. Three missense mutations in the PS1 gene (Ala246Glu in exon 7, Pro267Leu in exon 8, and Leu424Arg in exon 12) were found in patients from families with ADEOAD. In addition, the Glu318Gly noncausative polymorphism in exon 9 was detected in two unrelated sporadic EOAD cases. The variation was also absent from other 53 patients and 48 controls. Therefore, we could not confirm the previous suggestion that the Glu318Gly substitution may be a risk factor for AD.
Subject(s)
Alzheimer Disease/genetics , Membrane Proteins/genetics , Mutation, Missense/genetics , Adult , Amino Acid Sequence/genetics , Female , Humans , Male , Middle Aged , Molecular Sequence Data , Poland , Presenilin-1ABSTRACT
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.
Subject(s)
Alzheimer Disease/genetics , Amyloid beta-Protein Precursor/genetics , Brain/physiology , Presenilin-1/genetics , Presenilin-2/genetics , Age of Onset , Aged , Aged, 80 and over , Alzheimer Disease/pathology , Brain/pathology , Codon/genetics , Exons/genetics , Genes, Dominant , Genetic Counseling , Genome, Human , Humans , Middle Aged , Models, Genetic , Polymorphism, Single Nucleotide , Presenilin-1/chemistry , Protein ConformationABSTRACT
Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by memory loss and personality changes. Pathological hallmarks of AD are: deposition of amyloid plaques and neurofibrillary tangles in the brain, accompanied by neuronal and synaptic loss. The genetic background of AD is heterogeneous and strongly depends on the form of the disease. In most of the families with early-onset AD (EOAD) (10% of the total population of patients), the disease segregates as an autosomal dominant fully penetrant trait. To date, some missense mutations in three genes encoding the amyloid precursor protein, presenilin 1 (PS1) and 2 (PS2) have been found to cause familial EOAD. We screened for mutations in the presenilin genes in a sample of 55 patients with familial or sporadic form of EOAD from the Poznan region. We found 4 missense mutations in the PS1 gene: A246E in exon 7, P267L in exon 8, E318G in exon 9, and L424R in exon 12 among 5 unrelated patients. The frequency of PS1 mutations was 11% (5 of 55) in the whole sample of the patients with EOAD or 50% (3 of 6) if the analysis was restricted to familial cases with a positive history of dementia in the patient's family.
