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Down综合征是最常见的常染色体数目异常疾病 ,由 2 1号染色体减数分裂时不分离造成。母亲年龄≥ 35岁是发生Down综合征患儿的主要风险因素 ,但大部分的 Down综合征患儿出生时其母亲 <35岁 ,因此应寻找更多的风险因素以提高诊断水平。叶酸是人体必需的水溶性维生素之一 ,其活性形式四氢叶酸构成一碳单位转移酶的辅酶 ,影响 DNA的合成和DNA的甲基化。影响叶酸代谢的亚甲基四氢叶酸还原酶 (MTHFR)、甲硫氨酸合成酶 (MS)、甲硫氨酸合成酶还原酶 (MSR)和β-胱硫醚合成酶 (CBS)等基因的多态性可能是 DNA低甲基化造成染色体不分离的风险因素 ,遗传 (基因 )和环境 (营养 )两方面的因素均可导致染色体不分离而产生 2 1三体
Down syndrome is the most common anomalous number of autosomal chromosomes, caused by chromosome 21 meiosis does not separate. Mother age ≥ 35 years old is a major risk factor for Down syndrome. However, most children with Down syndrome are less than 35 years old at birth, so more risk factors should be sought to improve the diagnosis. Folic acid is one of the essential water-soluble vitamins, and its active form of tetrahydrofolate constitutes a coenzyme of carbon monomerase, affecting DNA synthesis and DNA methylation. Methyltetrahydrofolate reductase (MTHFR), methionine synthase (MS), methionine synthase reductase (MSR) and β-cystathionine synthase (CBS) genes that affect the metabolism of folic acid Polymorphism may be caused by hypomethylation of DNA is not a risk factor for chromosome segregation, genetic (gene) and environmental (nutrition) both factors can lead to chromosomal non-separation resulting from 2 1 trisomy