母胎间差异甲基化片段在无创性产前诊断中的应用价值

目的探讨HLCS、RASSF1A片段在母胎间甲基化状态的差异并评估其在无创性产前诊断中的应用价值。方法收集388例孕妇血浆,其中126例同时收集外周血细胞及胎盘（或绒毛）组织,采用甲基化敏感性限制性酶切联合荧光定量PCR（MSRE＋PCR）技术,检测母胎间HLCS基因、RASSF1A基因甲基化状态的差异,分析其影响因素,并根据孕妇血浆中胎源性HLCS/RASSF1A浓度比值判断胎儿21号染色体数目。结果研究证实HLCS及RASSF1A在胎盘或绒毛组织中均呈高甲基化状态,而在母体外周血细胞呈现低甲基化状态,且这种甲基化差异不受孕妇年龄、孕周、胎儿性别的影响。采用MSRE＋PCR技术对孕妇血浆中HLCS、RASSF1A片段的检出率分别为97.4%和96.9%。计算274例正常妊娠孕妇血浆中胎源性HLCS/RASSF1A比值,确定其95%的参考值范围为0.34～2.02,以此为标准判断102例胎儿21号染色体数目,其中98例二倍体妊娠的准确率为95.9%（94/98）,4例21三体综合征妊娠均获正确诊断。结论高甲基化HLCS、RASSF1A基因可作为孕妇血浆中胎源DNA的标志物,且有望根据孕妇血浆中甲基化HLCS/RASSF1A浓度比值进行21三体综合征的无创性产前诊断。     

Chorionic villi sampling for early prenatal diagnosis: an option for the Jewish orthodox community

The Jewish religion permits abortion up to 40 days after conception. To accommodate the Jewish orthodox community, prenatal diagnosis in the eighth gestational week may be a feasible goal with clear benefits. We present our experience with chorionic villus sampling (CVS), wherein out of 144 patients requesting CVS, 125 were found to be suitable for the procedure. Excluding patients with fundal placenta and cervical or uterine myoma, chorionic sampling was successfully performed on 102 out of 106 patients (96.2%) and a chromosome result was available for 98 of those patients (96%). Fetal losses, within 14 days following procedure, were 2 out of 125 (1.6%). No complications were encountered following the procedure. The cytogenetic analysis was improved by culturing CVS fragments for 48 h, after which clearer banding patterns could be observed. One of the CVS preparations, from a 7.2/7-week-old embryo was successfully examined. Short-term (6 days) cultures were used as an additional method for chromosome analysis, to extend and confirm results obtained by the direct method.     

Cytogenetic analysis of biopsied preimplantation mouse embryos: implications for prenatal diagnosis

Genetic diagnosis of enzyme deficiencies have been developed in mouse models using biopsied preimplantation embryos. A technique for preimplantation cytogenetic analysis was developed using embryos which were biopsied at the 4-cell, 8-cell and morula stage. Three culture methods were compared, using exposure directly to colchicine or preculture or overnight culture with subsequent exposure to colchicine. Some biopsies were lost through cell death (4.7-20.3%) and technical problems (11.1-27.8%), whilst others remained in interphase (13.0-46.5%). Air-dried preparations were successfully G-banded and karyotyped by modifying routine banding procedures. Biopsies placed directly into colchicine yielded the greatest mitotic index. However, chromosome morphology was unsuitable for G-banded analysis. After a short preculture, 71.4% of fixed 8-cell biopsies were karyotyped. The success of analysis of 8-cell biopsies is probably partly related to the higher mitotic index of intact embryos at this stage. Loss of chromosomes through scatter and chromosome overlapping limited analysis, particularly in biopsies with only one metaphase. The present success rate is not acceptable for the application of this technique to human prenatal diagnosis. However, it presents a useful tool for the study of chromosomal error at the research level.     

Diagnosing and preventing inherited disease: Detection of sickle gene by coelocentesis in early pregnancy: a new approach to prenatal diagnosis of single gene disorders

Coelomic fluid, placental tissue and maternal blood were collectedat 7–10 weeks gestation from each of 58 women undergoingelective termination of pregnancy for psychological indications.In all samples, a 364 bp fragment of the human -globin genespanning positions –23 to 341 was amplified. The restrictionendonuclease Ddel was used to detect the sickle mutation whichabolishes its restriction site. -Globin DNA was successfullyamplified from all samples. In 53 cases a normal maternal -globingenotype was detected. In three out of five cases, where thematernal haemoglobin phenotype was HbAS, heterozygosity forthe sickle mutation was demonstrated on analysis of coelomicfluid. In the remaining two cases a normal -globin genotypewas observed. Three further coelomic fluid samples were foundto be heterozygous for the sickle mutation. In these instancesthe maternal haemoglobin phenotype was normal, indicating paternaltransmission of the sickle gene. The results of the presentstudy have established that the diagnosis of sickle cell anaemia,and potentially other human single gene disorders, is feasibleby coelocentesis.     

The contribution of maternal serum markers in the early prenatal diagnosis of molar pregnancies

The aim of this study was to evaluate the usefulness of maternal serum markers in the early prenatal diagnosis of molar pregnancies. The ultrasound features, cytogenetic and histopathological findings of 10 cases of molar pregnancy diagnosed at 11-13 weeks of gestation were compared retrospectively with the maternal serum concentrations of human chorionic gonadotrophin (HCG), alpha fetoprotein (AFP), pregnancy-associated plasma protein A (PAPP-A) and pregnancy-specific beta1-glycoprotein (SP1). Free beta-HCG and intact HCG concentrations were very high [> or = 2.5 multiples of the median (MoM)] in all cases. AFP concentrations were extremely low in all cases of singleton complete moles (< or = 0.5 MoM) and were high in one case of twin complete mole, in one case of triploid partial mole and two cases of euploid partial mole (> or = 2.5 MoM). Serum PAPP-A and SP1 were high in complete moles. The combined use of ultrasound features, maternal serum proteins and fetal cytogenetic findings should enable the early differential diagnosis in utero and perinatal management of those molar pregnancies presenting with an anatomically normal fetus.     

Identification of fetal mesenchymal stem cells in maternal blood: implications for non-invasive prenatal diagnosis

Strategies for genetic prenatal diagnosis on fetal cells in the maternal circulation have been limited by lack of a cell type present only in fetal blood. However, the recent identification of mesenchymal stem cells (MSC) in first trimester fetal blood offers the prospect of targeting MSC for non-invasive prenatal diagnosis. We developed protocols for fetal MSC enrichment from maternal blood and determined sensitivity and specificity in mixing experiments of male fetal MSC added to female blood, in dilutions from 1 in 10(5) to 10(8). We then used the optimal protocol to isolate fetal MSC from maternal blood in the first trimester, using blood taken after surgical termination of pregnancy as a model of increased feto-maternal haemorrhage. In model mixtures, we could amplify one male fetal MSC in 2.5 x 10(7) adult female nucleated cells, yielding a 100% pure population of fetal cells, but not one fetal MSC in 10(8) nucleated cells. Fetal MSC were identified in one of 20 post-termination maternal blood samples and confirmed as fetal MSC by XY fluorescence in-situ hybridization (FISH), immunophenotyping and osteogenic and adipogenic differentiation. We report the isolation of fetal MSC from maternal blood; however, their rarity in post-termination blood suggests they are unlikely to have a role in non-invasive prenatal diagnosis. Failure to locate these cells routinely may be attributed to their low frequency in maternal blood, to sensitivity limitations of enrichment technology, and/or to their engraftment in maternal tissues soon after transplacental passage. We speculate that gender microchimerism in post-reproductive maternal tissues might result from feto-maternal trafficking of MSC in early pregnancy.     

Mutation spectrum of the MTM1 gene in XLMTM patients: 10 years of experience in prenatal and postnatal diagnosis

X‐linked myotubular myopathy (XLMTM) is a congenital neuromuscular disorder defined by severe hypotonia, respiratory failure and histopathologic changes in muscle biopsy. The objective of this report is to inform about our experience of genetic analysis on a group of 25 unrelated XLMTM patients, clinically diagnosed by several Italian and European Medical Institutes from 2006 to 2015. The molecular strategy used for genotyping involved Sanger sequencing of coding and intron/exon regions and the Multiplex Ligation Probe Amplification method. A total of 13 different point variants (6 nonsense, 5 missense, 1 splicing and 1 small deletion) were found in 15 patients (60%). Three were new missense variants: c.185G>T p.(Arg62Ile), c.719T>A p.(Val240Glu), and c.1262G>T p.(Arg421Leu). No large duplications/deletions have been identified. We performed carrier testing of at‐risk female relatives. Only one mutation was de novo. Successively, we offered XLMTM prenatal testing for seven pregnancies in five unrelated families. In this context, the aim to propose an effective molecular diagnostic service is to confirm clinical XLMTM diagnosis, to monitor the cause‐disease mutation segregation in the family and to offer genetic counseling to have correct information regarding offspring risks and the prenatal testing.     

New options for prenatal diagnosis in autosomal recessive polycystic kidney disease by mutation analysis of the PKHD1 gene

Due to the poor prognosis of severe autosomal recessive polycystic kidney disease (ARPKD), there is a strong demand for prenatal diagnosis (PD). Reliable PD testing is possible by molecular genetic analysis only. Although haplotype-based analysis is feasible in most cases, it is associated with a risk of misdiagnosis in families without pathoanatomically proven diagnosis. Linkage analysis is impossible in families where DNA of the index patient is not available. Direct mutation analysis of the recently identified polycystic kidney and hepatic disease 1 gene opens new options in families to whom a reliable PD cannot be offered on the basis of linkage analysis. We for the first time report two cases with PD based on mutation detection, illustrating the new options for PD in ARPKD.     

三个新的PAH基因短串联重复序列多态性及其在苯丙酮尿症产前诊断中的应用

目的提高经典型苯丙酮尿症的产前诊断的成功率。方法在苯丙氨酸羟化酶（phenylalanine hydroxylase，PAH）基因附近选择了3个新的短串联重复序列（short tandem repeat，STR）位点（PAH26、PAH32和PAH9），进行扩增长度片段多态性分析，确定它们在中国人群的分布及在诊断中的应用价值。结果3个新的STR位点的多态信息含量分别为0．518（PAH26）、0．413（PAH32）和0．362（PAH9）。这3个位点之间，PAH9与第3内含子中的STR位点（TCTA）n之间存在连锁不平衡，其他位点组合不存在连锁不平衡。联合第3内含子中的STR位点（TCTA）n和2个新的位点，可以对家系中突变基因标记进行95％N断，并成功地用于4例产前诊断中。结论选择性地应用PAH基因中的3个STR位点组合，可以95％地区分经典型苯丙酮尿症家系中父母的两个基因，从而准确地进行快速产前诊断。     

Non‐invasive prenatal diagnosis for single gene disorders: experience of patients

The aim of this study is to explore women's experiences of using newly developed non‐invasive prenatal diagnosis (NIPD) for single gene disorders. Methods used in this study include qualitative one‐to‐one interviews with eight women with pregnancies at risk of achondroplasia, Apert syndrome, thanatophoric dysplasia or a neuromuscular condition. The results of the study show that the women were positive about an accurate, safe, and early test. Where the foetus was at increased risk of inheriting a genetic condition, the benefits of NIPD over invasive testing were that it reduced the period of uncertainty and worry by being conducted within the first trimester. For those women for whom there was a low recurrence risk, the period of uncertainty could be reduced and pregnancy ‘normalized’ earlier. For women who would not have risked invasive testing, NIPD enabled them to have an early diagnostic test that was more accurate than ultrasound. Where ultrasound abnormalities were detected, NIPD ended the ‘diagnostic odyssey’, enabling women to make practical and psychological preparations for the birth. NIPD conducted through specialist services was considered most appropriate. NIPD for these particular single gene disorders was appreciated by women and appears to be satisfactory. Further exploration of stakeholder views may be required to inform more widespread implementation of NIPD for a broader range of genetic conditions.     

The arylsulphatases of chorionic villi: potential problems in the first-trimester diagnosis of metachromatic leucodystrophy and Maroteaux-Lamy disease

Three pregnancies at risk for late infantile metachromatic leucodystrophy have been monitored using chorionic villus biopsies. In the first of these a false negative diagnosis was made following assay of arylsulphatase A in villi. Subsequent studies have shown that this error was probably due to interference from another sulphatase in the villi, although the possibility that maternal contamination was also partly responsible could not be excluded. For reliable prenatal diagnosis of metachromatic leucodystrophy using chorionic villi it is advisable that studies with the nitrocatechol substrate are carried out on fractionated homogenates, or that the natural substrate is used. Problems may also occur when chorionic villi are used for assay of arylsulphatase B for first trimester diagnosis of Maroteaux-Lamy disease.     

The CpG island in intron 22 of the factor VIII gene is predominantly methylated on the X chromosome of human males

The inactivation of one of the two X chromosomes in females is a random process associated with methylation principally in CpG islands. The methylation status of a CpG island in intron 22 of the human factor VIII (FVIII) gene was investigated using a novel practical approach. Genomic DNA from men and women was digested with various methylation-sensitive (MS) restriction enzymes, the recognition sequences of which occurred at least once in the FVIII CpG island. Long distance-polymerase chain reaction (LD-PCR) was then used to amplify the island. Successful amplification indicated that the island was methylated and the absence of a PCR product indicated that at least one restriction site was unmethylated. To analyze the relative methylation status of the extragenic and intragenic copies of the island, we used Southern blot with MS restriction enzymes. The MS LD-PCR patterns obtained from male and female DNA samples indicated that at least some copies of the intragenic CG island were fully methylated at all sites investigated. Additionally, the island showed consistent differences among individuals. Southern blot studies using female DNA showed partial resistance to MS digestion for the intragenic and extragenic CpG island homologs. Our observations indicate that this CpG island is predominantly methylated on the X chromosome of males and suggest that its methylation pattern does not correlate with X inactivation of females. This prevents the use of this island coupled with DNA polymorphisms for investigation of X-chromosome inactivation. Received: December 4, 2001 / Accepted: February 12, 2002     

一个糖原累积病Ⅱ型家系的酸性-α-葡萄糖苷酶及其产前基因诊断

目的 为1个糖原累积病Ⅱ型(glycogen storage disease typeⅡ,GSDⅡ)家系进行酶学和产前基因诊断.方法 用酸性-α-葡萄糖苷酶(acid-alpha-glucosidase,GAA)特异性水解荧光底物4-甲基伞型酮-α-D-吡喃葡萄糖苷(4-methylumbelliferyl-α-D-glucopyranoside,4-MUG)和阿卡波糖抑制其同工酶的方法检测外周血白细胞和羊水细胞GAA酶活性,聚合酶链反应扩增GAA基因外显子编码区序列,直接测序分析GAA基因突变情况.结果 先证者外周血白细胞与胎儿羊水细胞GAA酶活性均明显低于正常参考值范围,分别为正常对照平均值的12.3% 和1.1%.先证者和胎儿均携带新无义突变 p.W738X 和已报道的无义突变p.E888X;先证者、母亲和胎儿均携带假性缺陷等位基因[c.1726G>A; c.2065G>A].结论 通过GAA酶活性检测结合GAA基因分析对1个GSDⅡ家系进行了产前诊断.由于假性缺陷等位基因可引起GAA酶活性降低,故GAA基因分析应作为亚洲人群GSDⅡ产前诊断的常规手段.

Abstract：

Objective To carry out prenatal diagnosis for a glycogen storage disease typeⅡ(GSDⅡ) affected family. Methods The acid-α-glucosidase (GAA) activity was measured in whole leukocytes and cultured amniocytes with 4-methylumbelliferyl-α-D-glucopyranoside as substrate and with acarbose as inhibitor. The coding regions of GAA gene were amplified by polymerase chain reaction and analyzed by direct DNA sequencing. Results The proband and the fetus had low GAA activity (12.3% and 1.1% of the average normal range, respectively). Mutation analysis of the GAA gene revealed a novel nonsense mutation p.W738X and a reported nonsense mutation p.E888X in both the proband and the fetus; the reported pseudodeficiency allele c.[1726G>A;2065G>A] was found in the proband, the mother and the fetus. Conclusion The proband and the fetus were both GSDⅡaffected. A combination of GAA activity analysis and mutation analysis is efficient for the prenatal diagnosis of GSDⅡ. Mutation analysis should be a routine method in the prenatal diagnosis of GSDⅡ in Asian population, where pseudodeficiency allele can cause low GAA activity in normal individuals which is relatively common in Asian.     

Glycinelserine ratios in amniotic fluid: an unreliable indicator for the prenatal diagnosis of nonketotic hyperglycinemia

A series of 183 amniotic fluid samples from pregnancies with normal outcome were examined to assess the validity of the glycine/serine ratio in the prenatal diagnosis of nonketotic hyperglycinemia. The glycine/serine ratios in our series span a range of values which includes those of the previously reported control group as well as those values of a fetus with nonketotic hyperglycinemia. These data indicate that the glycine/serine ratio in the amniotic fluid of a pregnancy at risk for nonketotic hyperglycinemia is not a reliable indicator for the prenatal diagnosis of this disorder.     

Invited editorial essay: The legal implications of refusing to provide prenatal diagnosis in low-risk pregnancies or solely for sex selection

As more people learn about prenatal diagnosis, medical personnel are increasingly being asked to perform these procedures in both low-risk pregnancies and for purposes of sex selection. Analysis of present legal rules illustrates that it is highly unlikely genetic counselors will be subjected to legal liability for refusing to provide prenatal diagnosis in these situations. This freedom from liability will probably continue into the foreseeable future, despite recent developments in the areas of informed consent and allocation of scarce medical resources that tend to limit the traditionally broad deference given to medical personnel.     

A 15‐year‐long Southern blotting analysis of FMR1 to detect female carriers and for prenatal diagnosis of fragile X syndrome in Taiwan

Here, we review the results of Southern blotting analyses of the FMR1 gene performed in our reference laboratory in Taiwan over a 15‐year period. In total, 725 high‐risk women with a family history of fragile X syndrome (FXS) or idiopathic intellectual disability, 3911 low‐risk pregnant women without such family history, and prenatal diagnosis data for 32 foetuses from 24 carrier mothers were included. Only 2 carriers were in the low‐risk group, which indicated a prevalence of 1 of 1955 women (95% confidence interval: 1/7156‐1/539). A total of 100 carriers were found to be in the high‐risk group, thus revealing a significantly higher frequency than the low‐risk group (100/725 vs 2/3911, P<0.0001). Eight of the 14 foetuses that inherited the maternal mutant allele were verified to have a full mutation, with the smallest maternal pre‐mutation allele carrying 56 CGG repeats. The overall findings confirmed that the carrier prevalence among low‐risk women in Taiwan is significantly lower than that reported in western countries. Therefore, the most important step for preventing FXS in Taiwan would be to focus on high‐risk women by promoting general awareness of this disease and spreading knowledge regarding the benefits of carrier screening and prenatal testing.     

The introduction of QF-PCR in prenatal diagnosis of fetal aneuploidies: time for reconsideration

Quantitative fluorescent polymerase chain reaction (QF-PCR) has recently entered the field of prenatal diagnosis to overcome the need to culture fetal cells, hence to allow rapid diagnosis of some selected chromosomal anomalies. We reviewed the studies on the accuracy of QF-PCR in detecting chromosomal anomalies at prenatal diagnosis. Overall, 22 504 samples have been analysed. The detection rate of aneuploidies of the selected chromosomes (13, 18 and 21, and X and Y) was 98.6% (95% confidence interval 97.8-99.3). QF-PCR might play a major role and be considered a valid alternative to the full karyotype. Being less expensive, and almost entirely automated, more women could undergo invasive prenatal diagnosis without significant increase in health expenditure. By using QF-PCR as a stand-alone test, the chances of non diagnosing the commonest, and the only chromosome anomalies which do increase in frequency with maternal age, are approximately one in 150 abnormal karyotypes, or one in 10-30 000 samples, based on the age distribution. These error rates might be deemed acceptable, although most structural chromosomal anomalies will be missed. At present, women are rarely informed about the full spectrum of the conditions which might be diagnosed via amniocentesis or chorionic villous sampling. Some of these anomalies might be acceptable, in view of their limited or uncertain clinical relevance, and decision analysis might, in the majority of cases, confine the full karyotype to selected women who have specific indications.     

Stability of the m.8993T->G mtDNA mutation load during human embryofetal development has implications for the feasibility of prenatal diagnosis in NARP syndrome

Background

Mitochondrial DNA (mtDNA) mutations cause a wide range of serious genetic diseases with maternal inheritance. Because of the high transmission risk and the absence of therapy in these disorders, at‐risk couples often ask for prenatal diagnosis (PND). However, because heteroplasmy load (coexistence of mutant and wild‐type mtDNA) may vary among tissues and with time, the possibility that a single fetal sample may not reflect the whole neonate impedes prenatal diagnosis of mtDNA diseases.

Methods

We performed 13 prenatal diagnoses for the NARP (neurogenic weakness, ataxia, retinitis pigmentosa) m.8993T→G mtDNA mutation (p.Leu156Arg) in the ATP synthase subunit 6 gene. Analyses were performed on chorionic villous (CVS) and/or amniocyte samples carried out at various stages of pregnancy, using a method enabling quantification of low DNA amounts.

Results

Maternal mutant loads ranged from 0 to 75% in blood and had no predictive value for the fetus status, except for women with no detectable mutant DNA, whose fetuses were consistently mutation‐free. In 8/13 PND, mutant load was <30%. These children are healthy at 2–7 years of age. In 5/13 PND, mutant load ranged from 65 to 100%, and parents preferred to terminate the pregnancies (15–22 weeks of gestation). Single‐cell analysis of 20 trophoblastic cells and 21 amniocytes isolated from two affected fetuses found an average mutant load close to the overall CVS and amniocyte mutant load, despite striking intercellular variation. The m.8993T→G mutant loads, assessed in 7, 17, 11, and 5 different tissues from 4 terminations, respectively, were identical in all tissues from a given individual (mean (SD) 78 (1.2)%, 91 (0.7)%, 74 (2)%, and 63 (1.6)% for the 4 fetuses, respectively).

Conclusions

Our results indicate that the placental/amniotic mutant loads do reflect the NARP mutant mtDNA load in the whole fetus, even when the sample amount is small, and suggest that heteroplasmy level remains stable during pregnancy, at least after 10 weeks of gestation. Although these data establish the feasibility of PND for this mutation, assessing more precisely the correlation between mutant load and disease severity should further help in interpreting PND results.