| Background Alzheimer's disease (AD) is an acquired intelligence drops syndrome with clinical manifestations as memory decline and other cognitive dysfunction. It is usually occult in onset, advances gradually and presents with diffuse encephalatrophy, especially in the temporal, parietal and prefrontal lobe. It also presents with marked dilation of the third ventricle and intralateroventricle and marked atrophy of hippocampus. Pathologically, AD is characterized by neurofibrillary tangles in the neurons, extracellular deposition of amyloid within senile plagues and cerebrovascular amyloidosis. The accumulation of amyloidβpeptide in the brain is the main cause of neuron death.SORL1 gene is a newly discovered virulence gene for AD, involves the cleaving processes of amyloid precursor protein (APP) and increases the risk of late-onset sporadic Alzheimer's disease (SAD), but the morbidity is not identical among species. Gene expression studies show that SORL1 is significantly reduced in brain tissues of AD patients compared with controls and even the half of the healthy elderly. However, studies are rare in our country on the gene expression and mutation of SORL1 in peripheral blood samples. Hence, in the present study we evaluated the correlation between SORL1 gene and late-onset SAD in the Chinese population through detecting the mRNA expression and gene mutation of SORL1 in peripheral blood samples, which could provide a new clue for early diagnosis of AD. Two parts are included in this study:Part 1 Study on relationship between mRNA expression of SORL1 genes and Alzheimer's diseaseObjective To explore the mRNA expression of SORL1 genes in peripheral blood samples from Chinese patients with late-onset SAD.Methods Twenty-three patients with late-onset SAD diagnosed according to the clinical diagnosis criteria given in NINCDS-ADRDA and the 10th revision of WHO Disease Classification were selected as SAD group and 12 healthy persons served as control group. Leucocytes we- re isolated from peripheral blood samples and RNA was extracted. Fluorescence quanti- tative polymerase chain reaction (PCR) was performed to determine the mRNA expre- ssion of SORL1, which was normalized against glyceraldehydes phosphate dehydrog- enase mRNA.Results The expression of SORL1 mRNA in peripheral blood samples from patients with Alzheimer's disease was significantly lower than that in the control group (0.392±0.286vs1.174±0.325, P<0.01for the control group, P<0.01), and the incidence of SAD was not influenced by age or gender.Conclusion Low expression of SORL1 mRNA is significantly correlated with late-onset SAD in Chinese patients. This suggests that fluorescence quantitative PCR may offer a powerful tool for diagnosis of late-onset SAD.Part 2 Study on relationship between mutation of SORL1 genes and Alzheimer's diseaseObjective To study the SORL1 gene mutation in peripheral blood from Chinese patients with late-onset SAD.Methods Thirty-five patients with late-onset SAD were selected as SAD group and ten healthy persons served as control group. Peripheral blood mononuclear cells were isolated, total RNA was extracted and cDNA was synthesized by reverse transcription. According the standard base sequence of SORL1 gene, an upstream and a downstream primer were designed and subjected to PCR amplification and sequencing analysis.Results Variation from standard base T to C appeared in cDNA fragments at the 5813 base position in one patient of the SAD group. The mutation rate was 2.9%. There was no gene mutation at cds region in the remaining patients and the control group.Conclusion Finding the location of base sequence 5813 in cDNA of SORL1 gene will play a guiding role in early diagnosis of late-onset SAD and may provide theoretic-cal guidance for further functional study. |
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