Backgrounds: Down syndrome (DS) is the most common chromosomal abnormality. The most important factor in DS is increased maternal age so after the age of 35, the risk of Down syndrome in pregnancy increases. Down syndrome can be diagnosed during pregnancy by prenatal screening. Nondisjunction in cell divisions is the main cause of the DS. Apo lipoprotein E is a 317 amino acid glycoprotein that plays an essential role in metabolism and cholesterol transport. Alzheimer’s disease (AD) is one of the symptoms of adults with DS. The apoE allele e4 has been identified as a risk factor for AD and also, played a main role in nondisjunction. An increased risk of AD in mothers of adults with DS has been reported. We hypothesized that young mothers of DS children (<35 age) could have an increased frequency of apoE allele E4 so we studied apoE allele distribution in cases of trisomy 21 and their parents. In present study, we investigated association of 112 codon of APOE gene C/T and 158 codon of APOE gene C/T with DS children and their parents in Northeast of Iran (Khorasan Razavi Provence). Methods: In this case-control study, 33 DS children and their parents were compared in case of age with 90 families without any history of DS. Genotyping was performed by ARMS-PCR technique. Statistical analysis was performed by SPSS v.21 software. Results: It indicated that there is a significant difference in allele distribution between case and control groups. The C allele for 112 codon of APOE gene and the C allele for 158 codon of APOE gene may associate with nondisjunction. In 112 codon of APOE gene, it seems having T allele reduces the risk of nondisjunction and in contrast C allele may be a risk factor in happening of nondisjunction. (p-value = 0.000006, OR = 2.66, 95% CI = 1.74 - 4.06). In 158 codon of APOE gene, it seems having T allele reduces the risk of nondisjunction and in contrast C allele may be a risk factor in happening of nondisjunction. (p-value = 0.0000, OR = 3.89, 95% CI = 2.38 - 6.34). E4 allele frequency in mothers of DS is about 14% more than those in control group. According to results of this study the C allele in 158 codon of APOE gene and the C allele in 112 codon of APOE gene could be considered as susceptibility genetic factors for nondisjunction in Northeast of Iran.
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