多重置换扩增(MDA)结合荧光PCR对植入前胚胎进行性别诊断的研究

目的:建立多重置换扩增(MDA)联合荧光PCR对植入前胚胎进行性别诊断的方法,为开展性连锁遗传病的性别筛选提供实验依据。方法:在行IVF-ET助孕的患者中,选取废弃的第3日新鲜或冷冻后的2PN受精胚胎。通过显微操作活检得到单个卵裂球细胞,采用MDA方法对单个/2个卵裂球细胞行全基因组扩增,然后采用荧光PCR方法对AMEL、X22、SRY和XHPRT 4个性染色体相关基因或STR位点进行扩增,对其扩增产物行毛细管电泳检测,分析电泳结果确定植入前胚胎的性别。以父母的外周血单个淋巴细胞作为对照进行分析。结果:①采用蛋白酶K法(n=21)和碱法(n=17)对卵裂球细胞进行裂解行MDA,扩增成功率未见统计学差异(85.7%vs 82.4%,P>0.05);单个卵裂球组(n=15)和2个卵裂球组(n=23)MDA扩增成功率亦未见统计学差异(80.0%vs87.0%,P>0.05)。②利用MDA方法对15个胚胎的单个/2个卵裂球进行扩增,扩增成功率为86.7%(n=13)。13个胚胎中7个为男性,6个为女性,性别检测成功率100%;等位基因脱扣(alleledropout,ADO)发生率为7.7%。结论:PGD中MDA是有效且可靠的全基因组扩增方法,MDA结合荧光PCR可以用于性连锁遗传病的性别筛选、致病基因检测和对胚胎进行HLA分型。     

结合多重链置换扩增和等位基因特异性PCR从单细胞中扩增脊髓性肌萎缩症运动神经元生存基因

目的:建立结合多重链置换扩增(multiple displacement amplification,MDA)全基因组扩增法和等位基因特异性PCR(allele-specific PCR,AS-PCR)对单细胞进行脊髓性肌萎缩(spinal muscular atrophy,SMA)诊断的方法。方法:对脊髓性肌萎缩症运动神经元生存基因(survival motor neuron gene1,smn1)7号外显子纯合缺失皮肤成纤维细胞及正常的皮肤成纤维细胞使用MDA法进行全基因组扩增,使用AS-PCR检测扩增产物的smn1和smn2基因,同时扩增D5S435、D5S351这2个微卫星位点,评估扩增效率、等位基因脱扣(allele dropout,ADO)率及污染检测。结果:对18个SMA细胞和21个smn1基因正常的细胞进行扩增。smn1和smn2基因扩增成功率分别为90.4%(19/21)和94.8%(37/39)。2个微卫星的扩增成功率为82.1%(32/39)和88.9%(16/18),ADO率分别为16.22%(6/37)和12.5%(2/16)。总扩增成功率为88.89%(104/117),总ADO率为15.09%(8/53)。结论:建立了结合MDA和等位基因特异性PCR对单个细胞进行smn1、smn2基因的扩增方法,为SMA单细胞植入前诊断奠定了基础。     

孕妇血浆中胎儿DNA检测在产前诊断中的应用

目的 探讨孕妇血浆中提取胎儿游离DNA,鉴别胎儿性别以诊断胎儿遗传性疾病的方法。方法 选择妊娠7-38周,B超确诊为单胎,经绒毛和羊水细胞染色体检测,确诊为妊娠男性胎儿的正常孕妇16例,妊娠女性胎儿的正常孕妇8例;X性连锁遗传病（假性肥大性肌营养不良,血友病,色盲,无汗性外胚层发育不良症）家族史行产前诊断者4例,用酚提取法,纯化孕妇血浆中胎儿DNA,然后用巢式聚合酶链反应（PCR）技术测定男性胎儿睾丸决定因子（SRY）。结果 16例妊娠男性胎儿孕妇血浆中,胎儿游离DNA第1次巢式PCR测定,检出SRY基因扩增片段10例,第1次检出率为62.5%;经第2次巢式PCR测定。另6例全部检出SRY基因扩增片段,累计检出率为100%,妊娠女性胎儿的8例孕妇血浆中,均未检出SRY基因扩增片段,4例X性连锁遗传病家族史者均检出SRY基因扩增片段。结论 从孕妇血浆中提取胎儿游离DNA行胎儿性别诊断是一种快速,简便,准确的产前诊断方法。     

多次退火环状循环扩增技术在单细胞水平诊断脊髓性肌萎缩症的应用评估

目的:应用并评价多次退火环状循环扩增(multiple annealing and looping-based amplification cycles,MALBAC)技术在单细胞水平诊断脊髓性肌萎缩症(spinal muscular atrophy,SMA)基因变异的效率。方法:收集SMN1基因7号外显子纯合缺失、正常皮肤成纤维细胞以及废弃胚胎单个卵裂球细胞,分别使用MALBAC和多重链置换扩增(multiple displacement amplification,MDA)方法进行全基因组扩增(WGA)。Sanger测序检测SMN1及SMN2序列,并对3个微卫星位点进行连锁分析。结果:2种扩增技术的总扩增成功率、等位基因脱扣(ADO)率无统计学差异(P0.05);MALBAC组诊断准确率为91.7%(67/73),低于MDA组的96.1%(73/76)(P0.05)。结论:针对SMA疾病开展单细胞水平遗传学诊断,传统MDA方法略优于MALBAC全基因组扩增技术。     

定量多重PCR在筛查DMD携带者和产前诊断中的应用

基于抗肌萎缩蛋白基因(DMD)多个外显子进行对数增长期多重PCR(多聚酶链反应)产物定量分析的原理,本研究在改进Ioannou等方法基础上建立了假性肥大型肌营养不良症(DMD/BMD)定量多重PCR(QM-PCR)技术,应用于携带者筛查和产前诊断.运用多重PCR技术对12个DMD/BMD家系先证者的检测表明缺失一个或一个以上外显子的家系有7个(58.3%).QM-PCR证实7名缺失型患者中6名母亲是与缺失型患者相同的携带者(86.7%).1例检测出外显子缺失的DMD患者,其母亲及外祖母的外周血淋巴细胞DNA未发现任何DMD基因缺失,可以排除为携带者(13.3%).对一名肯定携带者妊娠9周的胎儿进行了性别测定和DMD检测,确诊胎儿为男性DMD患者.一例可能携带者在排除携带者基础上,进一步对妊娠胎儿产前诊断确诊为正常女婴.本研究的结果进一步证实了该技术筛查DMD携带者的可靠性.将本技术与其它技术相结合可明显改进DMD家系中携带者诊断的准确性,并可应用于谱系及多态性信息不详家系的携带者诊断.该技术对防止缺失型DMD患儿和携带者的出生有重要的意义.     

简并寡核苷酸引物聚合酶链反应扩增单细胞全基因组均匀性研究

目的　探讨单细胞简并寡核苷酸引物聚合酶链反应 (DOP PCR)扩增全基因组DNA的均匀性及植入前胚胎遗传学研究的新途径。方法　获取正常男女性、X单体、X、13和 2 1三体细胞 ,行单细胞DOP PCR ,通过比较基因组杂交 (CGH )双色荧光强度比变化 ,分析扩增均匀性。结果　 (1)DOP PCR产物 /正常男性基因组DNACGH :约 1/ 3常染色质区强度比均数及标准差超过正常允许范围 ,X染色体假性过度表达 ,13、2 1三体无明显变化。 (2 )DOP PCR产物 /正常男性单细胞DOP PCR产物CGH :94%强度比均数及标准差接近期望值 ,能显示正常男女性、X单体、X、13和 2 1三体染色体拷贝数变化。结论　单细胞DOP PCR扩增基因组DNA存在明显的不均匀性 ,但这种不均匀扩增是非随机的。如选择合适的参照 ,扩增产物可用于植入前胚胎等单细胞全基因组研究。     

胎儿人细小病毒B19感染与孕妇自然流产及胎儿先天性畸形的关系

目的 探讨胎儿人细小病毒B19（HPV B19）感染与孕妇自然流产、胎儿先天性畸形的关系。方法（1）以巢式聚合酶链反应法检测182例自然流产的胚胎组织标本（自然流产组）中HPV B19DNA,以40例正常的胚胎组织标本为自然流产对照组。（2）以巢式聚合酶链反应法检测66例先天性心脏病患儿的心肌组织标本（心肌组）HPV B19 DNA,同时收集37例先天性心脏病患儿的外周血与之配对行HPV B19-IgM的酶联免疫吸附试验检测;以30例非先天性心脏病患儿的心肌标本为心肌对照组。结果 （1）自然流产组中HPV B19 DNA阳性率为25.8%（47/182）,而自然流产对照组阳性率为5.0%(2/40)。（2）心肌组中HPV B19 DNA阳性率为18.2%(12/66),而心肌对照组阳性率为0%（0/30）。（3）配对标本中心肌HPV B19 DNA阳性7例,其外周血中HPV B19-IgM全部阴性。结论 HPV B19宫内感染可能与自然流产和先天性心脏病的发生有一定关系。     

RhD血型的基因诊断及临床应用

目的 :建立RhD血型基因诊断的方法并对胎儿RhD血型进行产前诊断。方法 :采用PCR方法 ,对 4 89例供血者 (其中Rh-2 3例 ,Rh+ 4 6 6例 )外周血标本和 2 7例胎儿羊水 /脐血标本进行RhD基因外显子 10及外显子 7特异性片段的扩增。结果 :凡扩增出 136bp一条特异性片段者判断为Rh-;扩增出 136bp和 186bp两条特异性片段者判断为Rh+ 。 2 3例Rh-供血者有 2 2例扩增出 136bp特异性片段 ,4 6 6例Rh+ 供血者均同时扩增出 136bp和 186bp特异性片段 ,该方法的灵敏度为 10 0 % ,特异度为 95 6 5 % ,假阳性率为 4 .35 %。 2 7例胎儿羊水 /脐血标本的扩增结果 ,1例Rh-,2 6例Rh+ 。结论 :PCR方法检测RhD基因型简便、快速 ,且和血清学检测结果吻合率高 ,可用于胎儿RhD血型的产前诊断。     

超促排卵和体外成熟人卵子中印迹基因H19和PEG1的甲基化状态

目的:探讨超促排卵(controlled ovarian hyperstimulation,COH)和未成熟卵母细胞体外培养(in vitro maturation,IVM)是否引起印迹基因甲基化异常。方法:采用单细胞低熔点琼脂糖包埋亚硫酸氢钠处理、半巢式PCR扩增及克隆测序的方法,检测人单个卵子印迹基因H19和PEG1的甲基化状态。结果:共检测分析了94个(58个来自COH,36个来自IVM)处于不同成熟阶段的卵子中H19基因和PEG1(MEST)基因的甲基化状态,分别有6个COH卵子和2个IVM卵子出现H19或PEG1的1～2个CpG位点甲基化异常。绝大多数COH卵子的H19(91.4%,53/58)和PEG1(91.7%,33/36)的所有检测CpG位点甲基化正常,H19和PEG1所有CpG位点的甲基化率分别为0.8%(8/1044)和99.4%(859/864)。结论:经超促排卵和体外成熟培养卵子的印迹基因H19和PEG1甲基化状态是正常的,1～2个CpG位点甲基化异常的卵子是否导致胚胎的基因印迹异常需进一步研究。     

分子生物学技术在植入前诊断中的应用

植入前诊断是产前诊断非常早的一种方法，目的是放弃携带严重遗传病的胚胎，将健康胚胎植入母体。两种主要的方法是聚合酶链反应（PCR）和荧光原位杂交（FISH）。PCR用于单基因病诊断，FISH用于染色体异常诊断。临床主要应用于存在遗传风险的患者如携带单基因病和染色体易位的患者。随着分子生物学技术的飞速发展，如比较基因组（CGH），全基因组扩增技术（WGA），引物延伸预扩增（PEP），间期核转换技术及DNA芯片技术（DNAchip）等PGD先进检测手段的应用，单细胞用于诊断单基因或多基因突变及染色体疾病，为期不远。     

Preimplantation genetic diagnosis (PGD) for Duchenne muscular dystrophy (DMD) by triplex-nested PCR

OBJECTIVES: Duchenne muscular dystrophy (DMD) is a lethal X-linked recessive disorder with an incidence of approximately 1 in 3500 males, caused by mutation in the DMD gene. About 2/3 of DMD cases are caused by gross DMD gene deletion mutations. The purpose of this study was to develop a series of single-cell multiplex-nested PCR protocols for preimplantation genetic diagnosis (PGD) of the most prevalent DMD deletions. METHODS: The protocols were developed on single blood leukocytes from normal males and females and patients with known DMD gene deletion. In the first reaction, 2 of 11 different primer sets (exons 4, 8, 12, 13, 17, 46, 47, 49, 50, 52 and intron 52) were used to allow the simultaneous amplification of different DMD loci and the SRY gender marker, in a single triplex-nested polymerase chain reaction (PCR). Aliquots of this reaction were then subjected to nested PCR in which each locus was amplified individually. Following the successful establishment of single-cell triplex-nested PCR in single leukocytes, the technique was employed in five clinical PGD cases. RESULTS: For each DMD locus, more than 50 single leukocytes from healthy controls and more than 100 single leukocytes from affected individuals with known deletions were analyzed. Amplification efficiency for each tested locus was 98-100%. The false-negative rates for each analysis taken separately was <1%. Taken together, however, the results of the triplex-nested PCR analysis had a false-negative rate of 0%. No contamination was detected in all wash-drop blanks tested. We subsequently performed 18 PGD cycles in 5 DMD carriers. A total of 156 embryos were biopsied and successfully analyzed. Of these, 39 affected embryos were detected and 50 unaffected embryos were transferred (mean = 2.9 +/- 1.1 embryos per cycle). These resulted in three biochemical pregnancies and three clinical pregnancies, all of which have culminated in the birth of normal offspring. CONCLUSION: Triplex-nested PCR using 2 of 11 DMD loci and the SRY gender marker allow PGD for >90% of DMD families with known deletions. These protocols are associated with a high amplification efficiency and accuracy.     

Allele-specific amplification for preimplantation genetic diagnosis (PGD) of spinal muscular atrophy.

We have developed a new allele-specific amplification method for the preimplantation genetic diagnosis (PGD) of spinal muscular atrophy (SMA; Werdnig-Hoffmann disease) from a single cell. This method is based on the detection of the deletion of exon 7 of the telomeric copy of the survival motor neurone (SMN(t)) gene. An oligonucleotide was designed to be specific to the SMN(t) nucleotidic sequence with exonic mismatch G (for SMN(t))-->A (for SMN(c)) at its 3' end. This test produces reliable PCR products in 95% of single lymphoblasts (85/88) tested as well as in 16/16 blastomeres from normal controls. Specificity analysis showed that we were able to detect homozygous deletion of the SMN(t) gene in 99% of single lymphoblasts (103/104) from a SMA patient. No contamination was detected in 68 blanks tested. Multiple cell and DNA dilution analysis revealed that the test is accurate and specific up to 100 pg DNA and should thus also be suitable for PGD at the blastocyst stage. This rapid procedure requires a single round of fluorescent PCR and no restriction digestion, while previously described single cell methods include nested PCR followed by restriction enzyme digestion. Two PGD cycles for SMA using this procedure were performed in our centre.     

Reduced allele dropout in single-cell analysis for preimplantation genetic diagnosis of cystic fibrosis

Background: For couples at risk of transmitting a known single-gene defect, preimplantation genetic diagnosis (PGD) allows the identification and transfer of only unaffected embryos followingin vitro fertilisation (IVF), single-cell biopsy at about the eight-cell stage, and genetic analysis by PCR. This technique therefore avoids the risk of terminating an affected pregnancy diagnosed later in gestation. Methods and Results: Using nested PCR, the F508 mutation causing cystic fibrosis can be detected in single cells and we previously reported successful PGD in a couple in whom both partners carry the F508 mutation. To date we have treated 12 couples in a total of 18 cycles. This resulted in five singleton births confirmed to be homozygous normal. Single blastomeres from disaggregated embryos which had not been transferred were analysed to confirm the original diagnosis and assess reliability in clinical practice. Amplification efficiency and accuracy were high, with blastomeres from embryos diagnosed as homozygous normal or affected. In a proportion of blastomeres from presumed carrier embryos, one of the parental alleles failed to amplify, apparently at random (allele dropout, ADO). A possible explanation is the relative inaccessibility of one of the target allele early in the PCR. To test this we have used single lymphocytes from F508 carriers and investigated the effects of various denaturation temperatures in the early cycles of amplification. Conclusion: Increasing the denaturation temperature reduced the rate of ADO without affecting amplification efficiency.Presented at the 5th Annual Meeting of the International Working Group on Preimplantation Genetics, Hamburg, Germany, June 28, 1995.     

Influence of mosaicism on sexing of human preembryos detected by the polymerase chain reaction

Purpose: Preimplantation sex determination using a single cell by the polymerase chain reaction (PCR) was investigated to elucidate the influence of mosaicism. Methods: The SRY and ZFX genes were coamplified as target sequences for the Y and X chromosomes, respectively. The sensitivity of the single and nested PCR method was examined initially followed by amplification of single amniocytes by the nested PCR. Then the sex of single blastomeres at the three- and nine-cell stages was determined by the nested PCR. Results: The nested PCR was 10⁴-fold more sensitive than the single PCR. Sex determination was possible in 97.5% (117/120) of the blastomeres tested. However, the correspondence rate for all blastomeres within a single embryo was only 60% (12/20 embryos). Among the remaining embryos for which sexing of all blastomeres was not consistent, only one blastomere showed findings indicating the presence of mosaicism (or pseudomosaicism). Conclusions: At least two blastomeres need to be assessed when determining the sex of an embryo in order to avoid misdiagnosis due to mosaicism (or pseudomosaicism).     

Preimplantation genetic diagnosis for sickle-cell anemia and for beta-thalassemia

We developed single-cell polymerase chain reaction (PCR) assays for preimplantation genetic diagnosis (PGD) in couples carrying mutations in the beta-globin gene. With PGD the genetic status of an embryo obtained after intracytoplasmic sperm injection (ICSI) is determined by PCR analysis in single blastomeres, allowing only healthy embryos to be transferred to the uterus. We carried out nine PGD cycles using fluorescent PCR for two couples in whom the partners carried sickle-cell trait. Both couples achieved pregnancies, one of which was spontaneously aborted. We have developed two beta-thalassemia PGD protocols: one for the analysis of the 25-26delAA and the IVS2+1G>A mutation, and the other for the simultaneous detection of the IVS1+6T>C and the IVS1+110G>A mutations. For the second protocol, both non-labelled PCR and later fluorescent PCR were used. Both protocols were applied in clinical cycles (two non-labelled PCR cycles and one fluorescent PCR cycle) for two couples. The patient with the fluorescent PCR-PGD cycle became pregnant. Overall, the three fluorescent PCR assays were accurate and reliable with amplification efficiencies of minimum 93% and allele dropout (ADO) rates between 0 and 12%.     

Clinical application of multiple displacement amplification in preimplantation genetic diagnosis

Multiple displacement amplification (MDA) is a technique used in the amplification of very small amounts of DNA. MDA is reported to yield large quantities of high-quality DNA. The applicability of MDA to single cells was recently demonstrated as a potential technique for preimplantation genetic diagnosis (PGD). This paper shows the first clinical application of MDA in PGD. Two cycles of PGD were performed in two diseases, resulting in two pregnancies. All the diagnoses given on blastomeres were confirmed on the non-transferred whole embryos. The blastomere diagnosis was coupled with short tandem repeat (STR) analysis (16 loci) in all cycles. Allelic drop-out (ADO) assessment and amplification efficiency were evaluated on 40 single lymphocytes derived from parents of each disease. ADO and amplification failure were 10.3 and 2.2% for beta-thalassaemia and 17.9 and 2.2% for cystic fibrosis respectively. HLA matching for A, B and DR was performed successfully on single cell for the beta-thalassaemia family using similar methods to genomic DNA. The PGD protocol used in all diseases consists of MDA amplification, followed by a standard polymerase chain reaction protocol. Although HLA matching was not applied to embryos, its feasibility was shown on single cell DNA amplified by MDA. Altogether, these data show the simplicity and reliability of performing PGD in combination with HLA matching and STR analysis using MDA.     

Multiplex nested PCR for preimplantation genetic diagnosis of spinal muscular atrophy

OBJECTIVE: Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder caused in most patients by homozygous deletion of the SMN1 gene. For a carrier couple at a 25% risk of affected offspring, preimplantation genetic diagnosis (PGD) offers an alternative to prenatal diagnosis and termination of affected pregnancies. Our objective was to develop an accurate and reliable single-cell multiplex nested PCR analysis for PGD of SMA. METHODS: The method was developed on single blood leukocytes, obtained from healthy controls and an adult SMA type III patient with a known homozygous deletion of SMN1 exon 7 and 8. Multiplex nested PCR on single cells was used to co-amplify exons 7 and 8 of SMN. Additional multiplexing was performed with the ZFX/ZFY gene for sexing. Following successful establishment of the multiplex nested PCR protocol in single leukocytes, the technique was employed for PGD in 4 patients for a total of 7 cycles. In 2 patients, sexing was simultaneously performed using ZFX/ZFY. RESULTS: 220 single leukocytes from a normal individual and 220 from an SMA patient were analyzed. Exon 7 of SMN1 was amplified in 99% of normal single leukocytes and in none of the SMA-affected leukocytes. Exon 7 of SMN2 was amplified in 100% of both normal and SMA-affected leukocytes. Exon 8 of SMN1 was amplified in 98% of normal cells and in none of the SMA-affected leukocytes. Exon 8 of SMN2 was amplified in 96% of both normal and SMA-affected leukocytes. Amplification efficiency was 99% for ZFX/ZFY. There were no false-negative results and no contamination was detected in all wash-drop blanks tested. Seven PGD cycles were performed in 4 SMA-carrier couples with successful molecular analysis of 34 embryos and a total of 15 normal embryos transferred in 7 cycles. One clinical pregnancy has resulted in the delivery of a healthy male. Amniocentesis performed at 17 weeks confirmed the correct diagnosis for both SMA and sexing. CONCLUSIONS: These results suggest that our multiplex nested PCR protocol offers an efficient and accurate method for PGD of SMA while enabling the simultaneous analysis of an additional loci.     

Preimplantation genetic diagnosis of X-linked retinoschisis

The aim of this study was to perform preimplantation genetic diagnosis (PGD) for X-linked retinoschisis using multiple displacement amplification (MDA) for whole genome amplification and linked markers to the RS1 gene. The study evaluates the ability of MDA to amplify the whole genome directly from a single blastomere. MDA products were used for polymerase chain reaction analysis of two polymorphic markers flanking the RS1 gene and a new X/Y marker, X22, to sex embryos in an X-linked retinoschisis PGD programme. Two couples in whom the wives were carriers of the RS1 gene mutation (599G-->A), previously identified in their families, were subjected to two PGD cycles each. The main outcome measure was the ability to analyse single blastomeres for X-linked retinoschisis using MDA. As a result, the development of an MDA-PGD protocol for X-linked retinoschisis allowed for the diagnosis of 20 embryos in the four PGD cycles performed. These were biopsied on day 3 of culture and analysed. Eight embryos were affected males and two embryos were female carriers. In summary, three healthy female and four healthy male embryos, and a female carrier embryo, were transferred 48 h after biopsy. One single pregnancy was achieved. This report shows that the MDA technique is useful for overcoming the problem of insufficient genomic DNA in PGD. It also allows the simultaneous amplification of different targets to perform diagnosis of any known gene defect and sexing test by standard methods and conditions.     

Experience in preimplantation genetic diagnosis for exclusion of homozygous alpha degrees thalassemia

OBJECTIVE: To report our experience in preimplantation genetic diagnosis (PGD) for the exclusion of homozygous alpha degrees thalassemia. PATIENTS AND METHODS: PGD was performed on nine couples with alpha degrees thalassemia genotype undergoing assisted reproduction. Oocytes were aspirated after ovarian stimulation and fertilized by intracytoplasmic sperm injection. One or two blastomeres were biopsied from the six- to eight-cell embryo. Single cell multiplex PCR of the normal and alpha degrees thalassemia alleles was performed for first round, followed by semi-nested PCR of the respective alleles using 5'-end labelled fluorescent primers. Only those embryos with a blastomere diagnosed as having at least one normal allele were selected for transfer. RESULTS: One hundred and twenty-six blastomeres from 82 embryos were analyzed. The rates of allele dropout was 10.2% and PCR failure 12.7%. Fifty-eight embryos (70.7%) had at least one normal allele, of which 31 were transferred to 13 prepared cycles and one triplet pregnancy achieved. The triplets showed no ultrasound features of homozygous alpha degrees thalassemia at 18 weeks and were delivered in healthy condition by caesarean section at 34 weeks. Their genotypes were confirmed by cord blood analysis. CONCLUSIONS: PGD for alpha degrees thalassemia is possible by single cell PCR. The transfer and successful implantation of unaffected embryos ensure birth of disease-free babies.