引物延伸预扩增法应用于β-地中海贫血患者胚胎植入前遗传学诊断--附一例报告

目的 探讨对β-地中海贫血进行胚胎植入前遗传学诊断(PGD)的方法。方法 两对夫妇双方均分别为密码子41-42(-TCTT)及插入序列(IVS)-Ⅱ654(c→T)突变杂合子,在本中心进行超排卵和体外受精-胚胎移植治疗,胚胎活检后应用全基因组扩增技术及反向点杂交进行胚胎PGD,根据诊断结果选择健康的胚胎移植入子宫。结果 2例患者共获卵35个,受精率为87％,共活检胚胎16个,获卵裂球25个,单卵裂球总扩增效率为84％,等位基因脱扣率为15％。2例患者共移植5个胚胎,1例获得妊娠,已分娩健康双胎。结论 应用引物延伸预扩增技术可对β-地中海贫血进行PGD,达到优生的目的。     

Successful polar body-based preimplantation genetic diagnosis for achondroplasia

Achondroplasia, the most common form of dwarfism, is a candidate for preimplantation genetic diagnosis (PGD) because a single mutation accounts for almost all cases. Multiplex fluorescent assay including the common G380R mutation in the FGFR3 gene and eight close polymorphic markers was developed. First and second polar bodies (PB) were used for PGD analysis. An affected woman was treated with routine long-protocol ovarian stimulation and puncture. In the first PGD cycle, out of four fertilized oocytes, PB analysis revealed two mutant oocytes, one with total amplification failure of the maternal allele and one with inconclusive results. In the second PGD cycle, 14 oocytes were retrieved following a higher FSH dose and by performing oocyte retrieval and by placing the patient in the anti-Trendelenburg position using abdominal pressure to allow all follicles to be drained. Following PB analysis, two embryos containing the wild-type FGFR3 allele were transferred. This led to an uncomplicated pregnancy and delivery by Caesarean section at week 38 of a healthy boy, carrying the FGFR3 wild-type maternal allele. In conclusion, oocyte retrieval, while difficult in patients with achondroplasia, can be successfully performed. PB analysis is a reliable and sensitive method for PGD for maternal achondroplasia.     

Social sex selection by preimplantation genetic diagnosis

A personal view is presented, exploring the issue of social sex selection by preimplantation genetic diagnosis from the dual perspectives of protecting the autonomy of the couple and the professional duty of care. It is concluded that sex selection by PGD is acceptable in certain circumstances.     

First specific preimplantation genetic diagnosis for ornithine transcarbamylase deficiency

Ornithine transcarbamylase (OTC) deficiency is an X-linked dominant metabolic disorder with partial penetrance in heterozygous females. Affected boys usually die from hyperammonemia in the first few days of life, while clinical expression in carrier females ranges from no symptoms to neonatal death. A young couple whose boy had died of OTC deficiency in the neonatal period was referred to our genetic department for their subsequent pregnancy. The fetus was found to be affected, and after genetic counseling the pregnancy was terminated. Prenatal diagnosis of the third pregnancy identified a heterozygous female, who died after a normal birth at age 11 days from hyperammonemia. After this, the couple asked for preimplantation genetic diagnosis (PGD). We have developed a duplex nested PCR assay allowing the amplification of both the mutation and an informative restriction fragment length polymorphism (RFLP) located in the 3' end of the OTC gene. After nested amplification, allele identification was carried out for both loci by double restriction digestion and electrophoresis gel analysis. The co-amplification of both loci provided a means of detecting potential allele dropout or incomplete digestion. Two PGD cycles were carried out, a total of 14 embryos were analysed and a diagnosis could be obtained in 13/14 embryos. There were four unaffected male embryos, four heterozygous females and four unaffected females; the final embryo was an affected one of undetermined gender. In both cycles, three unaffected embryos could be transferred early on Day 4 post-insemination. The second cycle resulted in the birth of a baby boy devoid of the OTC mutation. This constitutes the first birth following PGD carried out by a French team.     

Successful application of preimplantation genetic diagnosis for hypokalaemic periodic paralysis

Hypokalaemic periodic paralysis is a rare dominant inherited disease where a person suffers sudden falls of circulating potassium concentrations, producing muscle weakness and sometimes severe paralysis. Attacks can occur as frequently as several times a day or once in a year. The age of onset is usually adolescence but symptoms can appear as early as 10 years of age. Muscle weakness can compromise vital functions such as breathing or swallowing and heart arrhythmias are also frequent during attacks. Preimplantation genetic diagnosis, an early form of prenatal diagnosis for couples at risk of transmitting inherited diseases, was used to prevent the transmission of this disease. Six polymorphic short tandem repeat or microsatellite markers (STR) closely linked to the CACNA1S gene were tested. Three fully informative markers were chosen to establish the disease-bearing haplotype in the family and to determine the genetic status of five embryos by multiplex fluorescent heminested PCR. Four of the five embryos tested were diagnosed as non-affected and one as affected. Two embryos were transferred resulting in a singleton pregnancy and the birth of a healthy girl.     

Successful preimplantation genetic diagnosis for alpha- and beta-thalassemia in China

METHODS & RESULTS: In southern China, the average carrier rates of alpha-thalassemia and beta-thalassemia in the population are as high as 10.3% and 2.8%, respectively. Because of the high rates, they are known as 'social diseases' in some regions. In this study, the fluorescent gap PCR, which can detect the alpha-thalassemia Southeast Asia deletion (SEA deletion), was applied in four clinical applications of preimplantation genetic diagnosis (PGD) on four couples, among whom both partners were alpha-thalassemia carriers. Two patients became pregnant and two healthy babies were born, which confirmed the PGD results. The single cell multiplex nested PCR followed by reverse dot blot (RDB), which can simultaneously detect the 16 beta-thalassemia mutations in the Chinese population, was applied in four clinical PGD cycles on four couples among whom both partners were beta-thalassemia carriers. One pregnancy was achieved and it resulted in a live healthy birth, which confirmed the results of PGD. The amplification efficiencies of the two protocols described above were 89.5% and 93.9%, respectively. The allele drop-out (ADO) rates of these two protocols were 5.9% and 10.9%, respectively. CONCLUSION: These studies represent the successful applications of PGD protocols that can detect more than 95% of alpha- and beta -thalassemia mutations in the Chinese population.     

Analysis of sex chromosomes in preimplantation genetic diagnosis for X-chromosome-linked disorders

Preimplantation genetic diagnosis (PGD) is diagnostic tool to avoid inheritance of genetic disease by transferring unaffected embryos. Recently, PCR and FISH have been mainly applied to the diagnosis of single gene disorders and chromosomal abnormalities, respectively. Since with PGD, only a few cells are available for genetic tests, both gene and chromosomes analysis have to be obtained from the same, limited material. Cell recycling makes it possible to obtain the information on genes as well as chromosomes from the same cells. Therefore cell recycling is an acceptable strategy where in PGD targets large proportions of embryos severe chromosomal abnormalities. The responsible genes of the X-linked disorder and numerical abnormalities of sex chromosomes should be analyzed simultaneously. Gender information is definitely useful because only male affected embryos should be avoided for transfer.     

The use of preimplantation genetic diagnosis in sex selection for family balancing in India

This paper describes the use of preimplantation genetic diagnosis (PGD) in sexing embryos for family balancing in a private IVF clinic in India from April 1999 to April 2001. Embryos were biopsied and analysed on day 3, cultured in sequential media and then transferred on day 4 or day 5 after morphological selection of the best embryos. From a total of 42 cycles started, 14 clinical pregnancies and nine live births have been achieved so far, with five ongoing pregnancies. The benefits of delayed transfer 24-48 h after the embryo biopsy are that PGD centres could use the extra time available to confirm the diagnosis or introduce additional diagnostic tests for the same embryo. The selection of blastocysts for transfer should also permit the transfer of fewer embryos, thus reducing the risk of multiple gestations and increasing the pregnancy rate as a consequence of the expected higher implantation rate. This is the first report of the use of PGD in sex selection for family balancing in India, where couples place a premium on having baby boys, and the social and ethical aspects of the use of this technology in this setting are briefly discussed.     

New perspectives on preimplantation genetic diagnosis and preimplantation genetic screening

Preimplantation genetic diagnosis is a procedure that involves the removal of one or more nuclei from oocytes (a polar body) or embryos (blastomeres or trophectoderm cells) in order to test for problems in genome sequence or chromosomes of the embryo prior to implantation. It provides new hope of having unaffected children, as well as avoiding the necessity of terminating an affected pregnancy for genetic parents who carry an affected gene or have balanced chromosomal status. Polymerase chain reaction-based molecular techniques are the methods used to detect gene defects with a known sequence and X-linked diseases. The indication for using this approach has expanded for couples who are prevented from having babies because they carry a serious genetic disorder to couples with conditions that are not immediately life threatening, such as cancer predisposition genes and Huntington disease. In addition, fluorescent in situ hybridization (FISH) has been widely applied for the detection of chromosome abnormalities. FISH allows the evaluation of many chromosomes at the same time, up to 15 chromosome pairs in a single cell. Preimplantation genetic screening, defined as a test that screens for aneuploidy, has been most commonly used in situations of advanced maternal age, a history of recurrent miscarriage, a history of repeated implantation failure, or a severe male factor. Unfortunately, randomized controlled trials have as yet shown no benefit with respect to preimplantation genetic screening using cleavage stage biopsy, which is probably attributable to the high levels of mosaicism at early cleavage stages and the limitations of FISH. Recently, two main types of array-based technology combined with whole genome amplification have been developed for use in preimplantation genetic diagnosis; these are comparative genomic hybridization and single nucleotide polymorphism-based arrays. Both allow the analysis of all chromosomes, and the latter also allows the haplotype of the sample to be determined. The promising results of these two approaches will inspire further validation of these array platforms, even at the single-cell level. It remains to be decided which embryo stage is the best for biopsy. Moreover, if randomized controlled trials are confirmed to play a role in increasing delivery rates, this will be a major step forward for assisted reproductive technology patients around the world.     

Successful pregnancy outcomes after preimplantation genetic diagnosis (PGD) for carriers of chromosome translocations

Reciprocal translocations are found in about 1 in 500 people, whereas Robertsonian translocations occur with a prevalence of 1 in 1000. Balanced carriers of these rearrangements, although phenotypically normal, may present with infertility, recurrent miscarriage, or offspring with an abnormal phenotype after segregation of the translocation at meiosis. Once the translocation has been identified, prenatal diagnosis can be offered, followed by termination of pregnancies with chromosome imbalance. Couples who have suffered repeated miscarriage or those who have undergone termination of pregnancy as a result of the translocation carrier status of one partner are looking increasingly to preimplantation genetic diagnosis (PGD) as a way of achieving a normal pregnancy. Similarly, infertile couples in which one partner is a translocation carrier may request PGD to ensure transfer of normal embryos after in vitro fertilization. Translocation PGD has been applied successfully in several centres worldwide and should now be considered as a realistic treatment option for translocation carriers who do not wish to trust to luck for a successful natural outcome.     

Successful pregnancy outcomes after preimplantation genetic diagnosis (PGD) for carriers of chromosome translocations

Reciprocal translocations are found in about 1 in 500 people, whereas Robertsonian translocations occur with a prevalence of 1 in 1000. Balanced carriers of these rearrangements, although phenotypically normal, may present with infertility, recurrent miscarriage, or offspring with an abnormal phenotype after segregation of the translocation at meiosis. Once the translocation has been identified, prenatal diagnosis can be offered, followed by termination of pregnancies with chromosome imbalance. Couples who have suffered repeated miscarriage or those who have undergone termination of pregnancy as a result of the translocation carrier status of one partner are looking increasingly to preimplantation genetic diagnosis (PGD) as a way of achieving a normal pregnancy. Similarly, infertile couples in which one partner is a translocation carrier may request PGD to ensure transfer of normal embryos after in vitro fertilization. Translocation PGD has been applied successfully in several centres worldwide and should now be considered as a realistic treatment option for translocation carriers who do not wish to trust to luck for a successful natural outcome.     

Non-disclosing preimplantation genetic diagnosis for Huntington disease

OBJECTIVES: Individuals at risk for Huntington disease face difficult decisions regarding their reproductive options. Most do not wish to pass on the gene for Huntington disease to their children, but may not be prepared themselves to undergo presymptomatic testing and learn their genetic status. For these reasons, many at-risk individuals with a family history of HD would choose a method of genetic diagnosis that would assure them that they can have children unaffected with HD without revealing their own genetic status (non-disclosing). We have shown that, with a carefully designed and executed programme of non-disclosing preimplantation genetic testing, one can successfully assist at-risk couples to have their own biological children who are free from Huntington disease, without forcing parents to confront knowledge of their own genetic status. METHODS: Couples where one partner was at 50% risk for Huntington disease underwent in vitro fertilization with preimplantation embryo biopsy and molecular analysis for Huntington disease where appropriate. RESULTS: After extensive counselling and informed consent, 10 couples underwent 13 in vitro fertilization and two frozen embryo transfer cycles in a programme for non-disclosing preimplantation genetic diagnosis for Huntington disease. In 11 cycles, embryos determined to be free of Huntington disease were transferred, resulting in five clinical pregnancies. One set of twins and three singleton pregnancies have delivered. One pregnancy resulted in a first-trimester loss. CONCLUSIONS: The option of non-disclosing preimplantation genetic diagnosis should be reviewed, along with other relevant medical options, when counselling at-risk Huntington disease families.     

Successful pregnancy after preimplantation genetic diagnosis in a female with Robertsonian translocation.

Preimplantation genetic diagnosis (PGD) is an alternative option for couples with chromosome abnormalities. A 34-year-old woman with balanced Robertsonian translocation [(45, XX, der(13; 14)(q10; q10)] requested PGD due to recurrent spontaneous abortion. Embryos of good quality were biopsied on day 3 post-oocyte retrieval. The aspirated blastomeres were fixed and analyzed using fluorescence in situ hybridization. In the first cycle, 2 unaffected embryos were transferred back without success. No unaffected embryo was available in the second cycle. On day 5 in the third cycle, 2 unaffected embryos were transferred resulting in a twin pregnancy. Amniocentesis confirmed the diagnosis. At the gestational age of 35 weeks, 2 healthy girls were born via cesarean section. Postnatal physical examination found no evidence of major abnormalities.     

Methods in preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) is a new strategy, orientated toward primary prevention of congenital anomalies in couples with reproductive risk, such as advanced maternal age, carriers of chromosomal abnormalities, and carriers of monogenic conditions. For these patients, PGD is an acceptable alternative to prenatal diagnosis, mainly in those countries where pregnancy interruption is forbidden by law. PGD effectively avoids the implications linked to traditional prenatal diagnosis. Centres that provide medical servicies on reproductive biomedicine are responsible for the development and improvement of this new prevention strategy. Thanks to advances in micromanipulation techniques, associated with recent progress in molecular genetics, PGD may be employed for any genetic condition in the future.     

Advances in preimplantation genetic diagnosis

Strategies for preimplantation genetic diagnosis (PGD) have become increasingly complex. For single gene disorders it is now usual for several DNA fragments to be simultaneously amplified using multiplex-PCR. This allows redundant diagnostic loci to be analyzed, reducing the chance of misdiagnosis due to allele dropout (ADO). Additionally, hypervariable 'fingerprinting' loci can be amplified, revealing the presence of DNA contaminants. Chromosomal screening has also increased in complexity. Current FISH techniques investigate up to nine chromosomes per cell and are offered to an increasingly wide range of patients, including women of advanced reproductive age and those with a history of repeated spontaneous abortion. Technical limitations, which preclude a full assessment of all chromosomes using FISH, have encouraged the development alternative tests. These include nuclear conversion, comparative genomic hybridization (CGH) and the use of DNA microarray 'chip' technology. This paper discusses technical innovations that have improved the scope and accuracy of PGD, as well as the emergence of new indications for PGD that are sometimes considered controversial (e.g. HLA-typing).     

Ethics of preimplantation genetic diagnosis

This paper briefly reviews the current status of preimplantation genetic diagnosis (PGD), to offer a basis for discussion about its ethical background. It describes the situation regarding modern types of PGD, which involve analyses on the inheritance by human embryos of chromosomal disorders or gene mutations. The current scale of these treatments is discussed, together with the progress of new advances such as ‘designer babies’. Brief reference is made to the first meeting in this series.