应用FQ-PCR方法快速产前诊断Down综合征

目的为探讨FQ-PCR方法快速、准确的应用于产前诊断Down综合征。方法分别提取46例外周血(包括16例确诊为Down综合征患儿和30例正常对照)和40例唐氏筛查高风险羊水细胞基因组DNA,FQ-PCR方法扩增基因D21S11、S100β(位于21号染色体)及基因UFD1L(位于22号染色体)。结果正常人羊水基因定量R1(D21S11/UFD1L)=1.095±0.213,R2(S100β/UFD1L)=1.087±0.146,Down综合征R1、R2分别为1.597±0.156、1.604±0.235,经t检验两组差异都有统计学意义。结论该方法无须细胞培养、操作简单,是一种快速准确产前诊断Down综合征的良好方法。     

Increased low-level chromosome 21 mosaicism in older individuals with Down syndrome

During a study of the familial aggregation of Down syndrome (DS) and Alzheimer disease (AD), we observed an increase in mosaicism for disomy 21 in older individuals with DS. In a total of 213 DS subjects who were studied cytogenetically, only 1 of 121 (0.8%) under age 45 exhibited mosaicism, while 14 of 92 (15.2%) who were age 45 or older had mosaicism. Mosaicism in this report connotes “low-level” mosaicism, where all 15 individuals exhibited a modal chromosome number of 47 (i.e., trisomy 21), and at least two cells lacked one of the three chromosomes 21. The occurrence of aneuploidy for chromosomes 15, 17, and X increased with age, and an inverse correlation between chromosome loss and size was also observed. Because older individuals had not been karyotyped at birth, it was not possible to determine whether our observations were due to either increased survival of mosaic individuals or accumulation of disomy 21 cells via increased chromosome loss with aging of the trisomy 21 individual. Using a modeling approach involving life table methods, we obtained results that suggested acquired mosaicism as the predominant mechanism to explain our findings. These results support the hypothesis that as individuals with DS age, there is an increased loss of chromosome 21. Am. J. Med. Genet. 68:147–151, 1997 © 1997 Wiley-Liss, Inc.     

孕中期超声软性标记在21三体综合征产前诊断中的作用

目的评价孕中期超声软性标记在21三体综合征产前诊断中的作用。方法对70例在孕中期因超声检查发现软性标记的孕妇进行产前诊断,超声软性标记包括胎儿颈皮厚度增加、双肾盂轻度分离、心室内强回声点、肠管回声增强、股骨及肱骨短小、脑室轻度扩张,其中仅含有一项超声软性标记的孕妇34例,含有两项或两项以上超声软性标记的孕妇36例,产前诊断方法采用羊膜腔穿刺术和脐血管穿刺术。结果在仅含有一项超声软性标记的34例孕妇中发现胎儿染色体异常5例,其中确诊21三体综合征4例,1例是染色体平衡易位。而含有两项或两项以上超声软性标记的36例孕妇未发现胎儿染色体异常。结论孕中期超声软性标记的出现增加胎儿21三体综合征的风险,特别对高龄孕妇或唐氏综合征血清筛查高风险的孕妇,应建议尽早产前咨询并考虑产前诊断。     

Parental age and the origin of extra chromosome 21 in Down syndrome

We present a report of the parental ages (n = 865) and parental origin of meiotic nondisjunction (n = 236) that are likely to show a predisposition in the etiology of Down syndrome (DS). Chromosomal analysis, performed over a 20-year period, on 1001 Down syndrome subjects, revealed pure trisomy 21 karyotype in 880 subjects (87.92%), mosaic trisomy karyotype in 77 (7.69%), and translocation karyotype in 44 (4.39%). The mean maternal age was found to be 30.34 years, and mean paternal age was 31.04 years. Nondisjunctional error was 79.24% maternal and 20.76% paternal. The findings of the study revealed the significant contribution of advanced parental age and increased maternal meiotic nondisjunctional error to the origin of trisomy 21 Down syndrome. Received: December 21, 2000 / Accepted: March 5, 2001     

同源基因定量PCR方法快速产前诊断Down综合征

目的　探讨同源基因定量PCR方法在预防Down综合征患儿出生及无创性产前诊断中的应用价值。方法　对178名正常对照和38例Down综合征患者同时扩增位于2 1号染色体Down综合征致病关键区域的人肝型磷酸果糖激酶基因(PFKL- CH2 1)和位于1号染色体的人肌型磷酸果糖激酶基因(PFKM- CH1) ,计算机软件(Fluor Chem V2 .0 Stand- Alone)分析PFKM- CH1及PFKL- CH2 1产物的相对比。结果　正常人比值为1.4 0±0 .36 7,Down综合征患者比值为0 .4 6±0 .2 1,经t检验差异有统计学意义。结论　这种定量PCR方法不但能检测2 1三体型,也可检测易位型Down综合征。     

唐氏综合征的无创产前诊断研究进展

唐氏综合征是最常见的染色体非整倍体遗传病,该病尚无有效治疗手段,出生干预是预防该病的有效措施。传统的产前筛查与产前诊断均具有一定的缺陷,无创产前诊断是未来发展的趋势。本文从母血胎儿细胞、母血胎儿游离DNA、母血胎儿游离RNA三个角度对目前唐氏综合征的无创产前诊断研究作一综述,以期对相关领域的研究发展有所帮助。     

Loss of the extra chromosome 21 in a patient with Down syndrome and myelodysplasia

Monosomy 21 is a rare acquired karyotypic abnormality associated with myeloid disorders. Occurrence of loss of one chromosome 21 in the background of trisomy 21 in Down syndrome, resulting in the pseudo-normalization of trisomy 21, is a novel finding. The case is described of a patient with Down syndrome who acquired such a genetic abnormality as a result of myelodysplastic syndrome.     

Down syndrome and the molecular pathogenesis resulting from trisomy of human chromosome 21

Chromosome copy number aberrations, anueploidies, are common in the human population but generally lethal. However, trisomy of human chromosome 21 is compatible with life and people born with this form of aneuploidy manifest the features of Down syndrome, named after Langdon Down who was a 19^th century British physician who first described a group of people with this disorder. Down syndrome includes learning and memory deficits in all cases, as well as many other features which vary in penetrance and expressivity in different people. While Down syndrome clearly has a genetic cause - the extra dose of genes on chromosome 21 - we do not know which genes are important for which aspects of the syndrome, which biochemical pathways are disrupted, or, generally how design therapies to ameliorate the effects of these disruptions. Recently, with new insights gained from studying mouse models of Down syndrome, specific genes and pathways are being shown to be involved in the pathogenesis of the disorder. This is opening the way for exciting new studies of potential therapeutics for aspects of Down syndrome, particularly the learning and memory deficits.     

Down syndrome: genetic recombination and the origin of the extra chromosome 21

Despite the clinical importance of trisomy 21, we have been ignorant of the causes of meiotic nondisjunction of chromosome 21. Recently, however, genetic mapping studies of trisomy 21 families have led to the identification of the first molecular correlate of human nondisjunction; i.e. altered levels and positioning of meiotic recombinational events. Specifically, increases in 0 exchange events or in distal-only or pericentromeric exchanges are significantly increased in trisomy 21-generating meioses. These observations have led to the idea that chromosome 21 nondisjunction requires 'two hits': first, the establishment in prophase I of a 'vulnerable' bivalent and second, abnormal processing of the bivalent at metaphase I or II.     

Duplication and loss of chromosome 21 in two children with Down syndrome and acute leukemia

Acute leukemia in Down syndrome (DS) is often associated with additional changes in the number or structure of chromosome 21. We present two DS patients whose leukemic karyotypes were associated with changes in chromosome 21 ploidy. Patient 1 developed acute lymphocytic leukemia (type L1); disomy for chromosome 21 was evident in all blast cells examined. Loss of the paternal chromosome in the leukemic clone produced maternal uniparental disomy with isodisomy over a 25-cM interval. The second patient had acute monoblastic leukemia (type M5) with tetrasomy 21 in all leukemic cells. DNA polymorphism analysis showed duplicate paternal chromosomes in the constitutional genotype. The maternal chromosome was subsequently duplicated in the leukemic clone. The distinct inheritance patterns of chromosome 21 in the blast cells of these patients would appear to indicate that leukemogenesis occurred by different genetic mechanisms in each individual. © 1995 Wiley-Liss, Inc.     

Age-associated chromosome 21 loss in Down syndrome: Possible relevance to mosaicism and Alzheimer disease

We previously observed low level mosaicism (2–4% normal cells) in phytohemagglutinin-stimulated peripheral blood lymphocytes (PBL) in 29% of a small group of elderly persons with Down syndrome (DS). An analysis of cytogenetic data on 154 trisomy 21 cases (age 1 day to 68 years) showed that the proportion of diploid cells in such cultures significantly increased (P < 0.005) with advancing age. Thus, the “;occult”; mosaicism in PBL of the elderly persons with DS is likely due to the accumulation of cells that have lost a chromosome 21. A consequence of chromosome 21 loss could be uniparental disomy of the 2n cells, a factor that might have significant biological consequences if some chromosome 21 genes are imprinted. Loss of a chromosome 21 from trisomic cells might result in tissue-specific mosaicism and “;classical”; mosaicism in different age groups. Chromosome 21 loss might also be relevant to the development of Alzheimer-type dementia in DS and in the general population. © 1993 Wiley-Liss, Inc.     

Asthma and atopy are associated with chromosome 17q21 markers in Chinese children

Background:  Single-nucleotide polymorphism (SNP)-based genome-wide association study revealed that markers on chromosome 17q21 were linked to childhood asthma but not atopy in Caucasians, with the strongest signal being detected for the SNP rs7216389 in the ORMDL3 gene. Such association was unknown in Chinese. This study delineated the allele and genotype frequencies of 10 SNPs at chromosome 17q21, and investigated the relationship between these SNPs and asthma and plasma IgE in southern Chinese children.
Methods:  Asthmatic children and non-allergic controls were recruited from pediatric clinics. Their plasma total and aeroallergen-specific IgE concentrations were measured by immunoassay. Ten SNPs on 17q21 region were genotyped by multiplex SNaPshot™, and their genotype associations with asthma traits analyzed using multivariate regression.
Results:  315 patients and 192 controls were enrolled. The allele frequency for C allele of rs7216389 varied significantly from 0.232 in our controls, 0.389 in Han Chinese to 0.536 in Caucasians. Asthma diagnosis was associated with rs11650680 and five other SNPs including rs7216389 ( P  =   0.019–0.034), whereas atopy was associated only with rs11650680 ( P  =   0.0004). Linear regression revealed the covariates for plasma total IgE to be significant for rs11650680 ( P  =   0.008–0.0002). Haplotypic associations were found with atopy and increased plasma total IgE, with the respective odds ratios and 95% confidence intervals for TTTCCGTT haplotype to be 0.21 and 0.09–0.52 ( P  =   0.0002) and 0.41 and 0.18–0.90 ( P  =   0.025).
Conclusion:  Childhood asthma and atopy are associated with chromosome 17q21 in Chinese, but such association may involve genes other than ORMDL3 in this region.     

A cost-benefit analysis of prenatal detection of Down syndrome and neural tube defects in older mothers

Infants of older mothers have an increased risk of Down syndrome. As public awareness of this disorder increases, so does the number of women requesting prenatal diagnosis for advanced maternal age. A cost-benefit analysis was done to determine the maternal age for which screening for Down syndrome is cost-beneficial. The analysis took into account the cases of neural tube defects which would be detected "incidentally" on amniocentesis, as all amniotic fluid samples have alpha fetoprotein levels measured. British Columbia (B.C.) provides a unique opportunity for such a study: single-year maternal age risk figures for Down syndrome based on virtually complete ascertainment are available; the Department of Medical Genetics Prenatal Diagnosis Clinic is the main referral centre for the province; B.C. has a universal medicare system which facilitates the calculation of medical costs and gives all women financially equal access to prenatal diagnosis. The study concludes that prenatal screening for Down syndrome is cost beneficial for women 34 years old or older at conception. A discount rate of 14% was chosen for this analysis and the effect of such a rate on the results is discussed.     

Call for change in prenatal counseling for Down syndrome

The American Journal of Medical Genetics Part A is to be congratulated for taking a leadership role by publishing a number of papers challenging the status quo of prenatal counseling for Down syndrome and of care for children and adults with Down syndrome. Parents want to know about the future abilities and potential of their fetus with Down syndrome, not simply negative medical information that may be outdated. Those providing counseling and those providing medical care could benefit from contact with individuals with Down syndrome outside the medical context. It is imperative that each person with Down syndrome be viewed as a unique individual with particular talents. Medical care providers should work with parents to help the child or adult with Down syndrome reach his/her goals.     

DNA sequences of chromosome 21-specific YAC detect the t(8;21) breakpoint of acute myelogenous leukemia.

The t(8;21)(q22;q22) is a nonrandom translocation specifically marking blasts of acute myelogenous leukemia (AML) with undifferentiated phenotype. The breakpoint on chromosome 21 involved by this rearrangement has been precisely localized relative to cloned DNA markers by physical and genetic linkage analysis enabling the use of positional cloning for its isolation. Yeast artificial chromosome (YAC) clones for loci proximal (D21S65) and distal (ERG) to the (21q22) breakpoint have been developed and their chromosome 21 origin and location relative to the breakpoint has been established. By using in situ hybridization analysis, a 240 kb YAC clone for the D21S65 locus clearly identified both derivative chromosomes of the (8;21) translocation in metaphase spreads of leukemia blasts with the rearrangement. The characterization of the DNA sequences contained in this 240 kb YAC can reveal the functional consequences of their derangement in leukemia with abnormalities of the (21q22) region.     

Physical mapping of chromosome 21 DNA markers in Alzheimer's disease region using somatic cell hybrids

From a chromosome 21 phage library, we selected 10 clones located proximal of the senile plaque amyloid precursor protein gene. Since a locus for Alzheimer's disease (AD) has been localized in the pericentromeric region of chromosome 21, the selected phage clones are potential candidate probes for genetic analysis of AD. In this study, we subcloned single-copy fragments of the selected phage clones, refined their physical localization, and examined their chromosomal distribution in relation to their position on chromosome 21. The results indicated that the phage clones are identifying nine chromosome 21 loci, which, if polymorphic, may be helpful in localizing the AD locus more precisely. Moreover, since all phage clones are located close to the centromere of chromosome 21, they can be used to determine the parental origin of nondisjunction in trisomy 21 with high reliability.