الفهرس 
Review of Literature
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Abstract
Alzheimer’s disease (AD) is the most widely recognized structure of dementia among more seasoned grown-ups. It is an age-related persistent condition described by progressive decay in memory, cognitive function, and physical status. Patients with AD lose their self-administration capacities .Furthermore; require long haul care as the disease advances. Currently, no treatment effectively reverses or halts the disease’s progression. Both genetic and environmental factors contribute to the disease’s development.
Telomeres, located at the ends of chromosomal DNA, consist of tandem repeats of the TTAGGG sequence (9-15 kb in humans). Functional telomeres enable replication and protect the genome from degradation and chromosomal fusion. When the telomere becomes critically short, the DNA damage repair system and cell-cycle inhibitors are activated; replicative senescence develops, followed by apoptosis. In fact, alterations in telomere length (TL) have been reported as critical factors in age-related diseases.
In this regard, this study aimed to Comparison and evaluation of the efficiency of TL measurement by (Q-FISH) and RT-PCR and Study of the environmental risk factors in the development in AD.
In the current work, blood samples were obtained from 30 AD patients assigned according to the detailed patient history in addition to 10 healthy volunteers as a control group.
All patients were subjected to clinical investigation, history taking including family history with laying stress on neuropsychological examination, (Q-FISH) technique on peripheral blood samples to assess the TL and relative TL measured by quantitative real-time PCR.
Firstly; the results of TL by Q FISH technique were revealed a significant difference between the AD patients and the controls, with a standardized mean difference 0.036. On the other hand, there was no a significant difference in the TL of patients and age (P = 0.985); furthermore gender (P = 0.428).In addition, there was a significant difference in TL of the group that has a hereditary history of Alzheimer’s disease and healthy group.
Secondly; the results of TL by RT-PCR technique were observed a significant difference of T/S ratio between the Alzheimer’s patients and their fold change in telomere length (P =0.0001).
The results of patients having a low fold change were showed a significant deference (P = 0.0002), also the groups of patients having high fold change were showed a significant deference (P = 0.018). The telomere shortening had been observed in various age related diseases like diabetes, hypertension and other environmental factors.
The current study estimated results of controlled hypertension patients a highly significant difference between T/S ratio and fold change of controlled hypertension patients with decreased fold change (P =0.0001), furthermore, there was a significant differences for controlled diabetes patient between T/S ratio and fold change (P = 0.0004).
In smoker patients, there was a significant difference between T/S ratio and fold change (P = 0.012) and in non-smoker patients a significant difference was found between T/S ratio and fold change (P = 0.004).
This study was found significantly correlation between the results of Real-time PCR and results of TL (Kb) Q-FISH by linear regression analysis; (r2) was =0.266 and P value was=0.004.
Moreover, there was a correlation between TL (Kb) and Fold change of telomeres by linear regression analysis (r2 =0.185 and P value was=0.018).
All of these results were explained that the telomere measurement by Q FISH technic matches with the relative results of Rt-PCR technic, also showed an inverse relationship between TL and the fold change.
In conclusion, this study proves that environmental factors are a major reason for shortening the telomere length of Alzheimer’s patients as diabetes, hypertension, smoking, and other factors of oxidative stress, inflammatory elements, lifestyle practice, and excess stress. Furthermore, the two measurement methods are considered good and reliable, with some limitations to each of them.