Thalassemia carrier screening and prenatal diagnosis among the British Columbia (Canada) population of Chinese descent

The goal of thalassemia screening is the identification, prior to the conception or birth of an affected child, of couples where both partners are thalassemia carriers. When both partners are identified as carriers for alpha- or beta-thalassemia, the risk of having a fetus who is homozygous or compound heterozygous for the abnormal gene is 25%. A study was performed to identify whether routine screening for thalassemia is indicated for the Chinese population in British Columbia (BC). In a population of 783 subjects, studied either prospectively or retrospectively, 5.0% were alpha-thalassemia carriers and 1.7% were beta-thalassemia carriers. In addition, a review of all BC cases of prenatal diagnosis for thalassemia over a 6-year period indicated that 26% of couples were identified as alpha-thalassemia carriers because of a second or third trimester diagnosis of fetal hydrops, and 17% of couples referred for beta-thalassemia already had an affected child. The experience with prenatal diagnosis shows that a significant proportion of at-risk couples are not identified prior to or early in a pregnancy. The prevalence of carriers for thalassemia would warrant a program of education and routine screening for this condition in the BC Asian population.     

The prevention of thalassemia in Sardinia

In this paper we review the characteristics and effectiveness of a program aimed at preventing homozygous beta-thalassemia in the Sardinian population. The target population for screening were couples at marriage, conception or early pregnancy. Awareness of the problem and the involvement of the population were achieved via the mass media or by personal approaches through lectures or discussions. Parents' Associations were consulted and have made themselves available to prospective couples in several critical areas. Education on thalassemias was introduced into the school curriculum. Counseling was based on private interviews at which the several options available were discussed with the individual carrier or the couples. Prenatal diagnosis was chosen by the large majority of couples counseled. The introduction of 1st trimester diagnosis resulted in a striking increase of the acceptance rate from 93.2 to 99.1%. Prenatal diagnosis was carried out initially by fetal blood analysis and thereafter by trophoblast or amniocyte DNA analysis. Direct detection of the mutation by oligonucleotide hybridization on agarose gel separated DNA fragments or by dot-blot analysis with allelic specific oligonucleotide probes on enzymatically amplified DNA was used. This program resulted in a decline in thalassemia major births of 90%. The reasons for residual cases were mostly lack of information and, less frequently, misdiagnoses or refusal of fetal diagnosis.     

A 12-year preventive program for β-thalassemia in Northern Sardinia

From 1980 to 1991, 6.3% of the adult population of the province of Sassari, Northern Sardinia, underwent voluntary β-thalassemia screening. Of the 28 000 subjects examined, 15.7% proved to be heterozygotes for β-thalassemia. In addition, the screening of 7500 students in 26 villages in Sassari province fixed the frequency of β-thalassemia in this part of Sardinia at 10.4%. Of the 539 couples at risk to be expected from this figure, the screening detected 43% (234). The data suggest that inductive screening played a major role in the efficiency of this preventive β-thalassemia program. Follow up of 221 pregnancies found to be at risk for homozygous β-thalassemia and referred to the Antenatal Diagnosis Service, Cagliari, Southern Sardinia, showed that antenatal diagnosis was carried out in 80% of them. The overall percentage of couples refusing antenatal diagnosis was 10.8%, but over the years the acceptance rate for the procedure increased from 87% to 96%. Atypical hematological findings in 1.5% of 468 members of the couples at risk required globin chain synthesis and molecular analyses to define the precise β-thalassemia genotype. Heterogeneous "mild"β-thalassemia mutations as well as coexisting δ-thalassemia were found in silent type I and type II β-thalassemia carriers which, without chain synthesis and DNA investigations, would have escaped detection.     

Counselling for prenatal diagnosis of sickle cell disease and beta thalassaemia major: a four year experience.

A non-directive programme of prenatal counselling was used during a four year period. Forty-three couples at risk for having a baby with a haemoglobinopathy were identified. Prenatal diagnosis was offered in 19 pregnancies to 14 couples at risk of having a baby with sickle cell anaemia and in two pregnancies in two couples at risk of a baby with beta thalassaemia major, who presented before the 18th week of pregnancy. Six couples at risk for sickle cell anaemia accepted prenatal diagnosis in 10 pregnancies, as did both couples at risk for thalassaemia. Couples who were eligible for prenatal diagnosis but refused it tended not to have been informed about sickle cell disease before counselling, one partner was more frequently absent at the time of the initial counselling session, or they either had no children with sickle cell disease or the children were not severely affected. Other factors influencing their decision included a poor obstetric history and rejection of abortion, mainly on moral grounds. The approximately 50% uptake of prenatal diagnosis in this initial study highlights the complex issues involved. Our experience indicates that with systematic screening and counselling in the antenatal clinic, and with increased awareness of the haemoglobinopathies, couples at risk will be in a better position to make informed decisions.     

Prevention of lysosomal storage disorders in Israel

Prevention programs for the detection of heterozygotes of relatively prevalent autosomal recessive diseases in various ethnic groups are available in recent years in Israel. Several lysosomal storage disorders (LSD) are included in this program. The goal of the program is the ascertainment of high risk couples before the birth of affected offspring. This is performed by a population screening program that addresses the specific needs and requirements of various population groups in Israel. The programs are supervised and designed by medical/clinical geneticists and are accompanied by genetic counseling prior to and after testing. Three types of population screening programs are in operation. The first type is offered to the general population and is directed to premarital and married couples. High risk families mostly opt for prenatal diagnosis. The second type is performed for diseases with a frequency of about 1:1000. This occurrence is common in Israel only in various Arab communities due to the high rate of consanguinity. The third type is a premarital screening performed by the Orthodox Jewish community and is operated by a nonprofit organization--"Dor Yeshorim". Two heterozygotes for a particular disease are advised not to proceed with the marriage and thus avoid the dilemma of prenatal diagnosis. Founder mutations of the relevant genes for each ethnic group are tested and the testing is tailored for each individual according to his/her ethnic background. Genetic counseling presents family planning options to high risk couples. These programs have resulted in a significant reduction in the birth of affected patients of the tested LSD a well as other recessive diseases in recent years.     

Molecular analysis and prenatal diagnosis of beta-thalassemia: about our experience in central Tunisia

Beta-thalassemia, by its high frequency and its heterogeneity, constitutes a real problem of health in Tunisia. Prenatal diagnosis by DNA analysis represents the only reality for couples at risk. The denaturant gradient (urea and formamide) on polyacrylamide gel electrophoresis has been performed in our laboratory, using psoralen as chemical clamps. This method is simple, reliable, safe, rapid, without radioactivity and has a reasonable cost (chemical clamps). Even if it needs an informatic modelization in other laboratories, this method seems to be adapted to our economic and work conditions and to the molecular heterogeneity of the Tunisian beta-thalassemia. We present the results of an epidemiological molecular study on 75 patients with beta-thalassemia and the results of ten prenatal diagnosis. The molecular lesions codon 39 (C-T) and IVS1 nt2 (T-G) are the most frequent in our study. This technical approach provides genetic counselling for at risk families by offering prenatal diagnosis (reducing as possible the cost and the delay of the result) after prealable family study and identification of the mutation(s).     

Efficiency of premarital screening of beta-thalassemia trait using MCH rather than MCV in the population of Fars Province,Iran

Iran is a country with high prevalence of about 5-10% of beta-thalassemia trait. The prevalence of Cooly's anemia has declined from 11.6 in 10000 population to 7.2 in 10000 in a five-year period due to screening program of beta-thalassemia trait before marriage. This study was conducted to compare the sensitivity of mean corpuscular hemoglobin (MCH) < 27 pg and mean corpuscular volume (MCV) < 80 fl as a screening test in first step of screening of beta-thalassemia trait. From 2449 couples (4898 cases) participating in the premarital screening to our clinic, 902 cases with either MCH < 27 pg, MCV < 80 fl, anemia, pallor or family history of beta-thalassemia were enrolled in the study. MCV, MCH as well as Hb A2 were measured in all cases. MCH and MCV had sensitivities of 98.5% and 97.6% for the diagnosis of beta-thalassemia trait, respectively. A false negative value of MCH is about 1% lower than that of MCV. MCH is a more sensitive screening test for detecting beta-thalassemia minor before marriage.     

Prenatal diagnosis of thalassemias and hemoglobinopathies

Thalassemia syndromes and hemoglobinopathies are of clinical genetic significance because of the severity of the sequelae associated with particular genetic constitutions in these conditions, their occurrence at high frequencies in certain populations of Mediterranean, African, and Asian origin, and the high frequency of recurrence in pregnancies of at risk families. Application of recently developed techniques of molecular genetics to the antenatal diagnosis of the most deleterious of these conditions (homozygous beta-thalassemia [Cooley's anemia], homozygous alpha-thalassemia [Barts hydrops fetalis], sickle cell anemia, and related severe homoglobinopathies) now affords parents the option to interrupt a pregnancy in which the fetus has the genetic constitution causing one of these abnormalities. The two different analytical strategies utilize fetal cells obtained by aminocentesis. In one, fetal blood is obtained either by sonographically guided placental aspiration or by aspiration from a placental vein directed by fetoscopy. Globin chain synthesis is monitored by the incorporation of radiolabelled amino acids in the isolated erythrocytes and the determination of the ratio of radioactive label incorporated into the various globin chains separated by column chromatography or electrophoresis. This technique is applicable to the antenatal diagnosis of alpha-and beta-thalassemia and to selected hemoglobinopathies. However, in the most experienced centers, fetal blood sampling is associated with a greatly increased risk of fetal loss. The other analytical approach utilizes desoxyribonucleic acid (DNA) isolated from fibroblasts to evaluate the presence of quantitatively and/or qualitatively normal DNA sequences, which constitute the structural gene(s) encoding specific globin polypeptide chains. This approach is most generally applicable to the detection of structural gene deletions as in a alpha-thalassemia; maternal and fetal risk is the same as that for conventional amniocentesis.     

Personal experiences of cystic fibrosis (CF) carrier couples prospectively identified in CF families

This qualitative study explores the experiences of cystic fibrosis (CF) carrier couples, prospectively identified in CF families, and the impact of the resulting genetic risk on reproductive behavior. Of the 12 couples identified until 1997, seven couples participated in semistructured interviews and two couples filled in a questionnaire, two to eight years after receipt of the test-results. After receiving the results, most couples reported that they were shocked, because they did not expect to both be carriers. More anxiety was expressed by those who were pregnant (n = 4) at the time of testing. There were reported difficulties in disclosing the results to family members, and the reactions of family members were not always supportive. After testing, some couples had problems with reproductive decision-making. All viable pregnancies (17 in 8 couples) were monitored by prenatal diagnosis; all affected pregnancies were terminated (6 in 4 couples). Couples who have live-born children after testing may subsequently have concerns during infancy about the correctness of the results of prenatal diagnosis and how to inform their children. Most couples did not regret the testing and, in general, the counseling was experienced positively, although some dissatisfaction was reported with regard to the psychological support received during pregnancy. Couples supported the idea of carrier screening in the general population, although various concerns were expressed. The results indicate a preference for testing before pregnancy. These findings may be useful in investigating possible dilemmas caused by the introduction of population carrier screening. Observations reported here might also apply to other recessively inherited disorders.     

A targeted population carrier screening program for severe and frequent genetic diseases in Israel

A national carrier screening program targeted at communities in which severe genetic diseases are present with a frequency higher than 1/1000 live births, has been in existence in Israel since 2002. Within the communities at risk, carrier screening is voluntary whereas genetic counseling and testing is provided free of charge. During the first 5 years of the program more than 13 000 tests were performed, and at the end of 2007 it was offered in 35 different localities/communities for a total of 36 diseases. Many of the couples identified to be at risk opted for prenatal diagnosis and in two cases an affected pregnancy was terminated. In some cases the couples declined prenatal diagnosis and two of those families gave birth to an affected child. Based on the experience learnt from this targeted screening program it appears that a knowledge-based, voluntary screening program operated within the community is an effective way to provide genetic services and test referrals. The community program directed toward couples in their reproductive period does not seem to have led to stigmatization at either the individual or the community level.     

Population screening in a Druze community: the challenge and the reward

PurposeThe Druze community is characterized by consanguinity and endogamy, and by reluctance to genetic testing and technological interventions for the prevention of birth defects. Multiple patients with four rare and severe inborn errors of metabolism cerebrotendinous xanthomatosis, prolidase deficiency, argininosuccinate lyase deficiency, and carbamyl phosphate synthetase I deficiency were identified in an isolated Druze village in northern Israel. The aims of this study were to identify couples at risk for four inherited diseases, and to prevent birth defects in a community presenting religious and cultural obstacles to genetic testing.MethodsA genetic screening and counseling program in a high-risk community.ResultsThe 1425 residents who attended group genetic counseling sessions between 2003 and 2007 consented to genetic testing. We identified 217 carriers for either one or two disease causing mutations. High carrier frequencies for cerebrotendinous xanthomatosis, prolidase deficiency, argininosuccinate lyase deficiency, and carbamyl phosphate synthetase I deficiency were identified as 1:11, 1:21, 1:41, and 1:95, respectively. Fifty-eight percent (125) of the carriers' spouses agreed to genetic counseling and testing. Ten couples at risk for affected offspring were identified and offered prenatal genetic counseling and diagnosis.ConclusionsThe genetic screening program, the first of its kind reported in a Druze community, was well received. We expect this program to increase awareness of genetic counseling, to contribute to disease prevention, and to serve as a model for other isolated communities.     

Pilot study of the acceptability of cystic fibrosis carrier testing during routine antenatal consultations in general practice.

BACKGROUND: In 1989, the gene for cystic fibrosis was cloned and it became possible to detect carriers of the gene among the general population, including pregnant women. AIM: The aim of the pilot study was to assess the acceptability of integrating cystic fibrosis carrier testing into antenatal care by general practitioners at the first booking appointment. METHOD: Between 1 September 1991 and 31 August 1992, inclusive, all patients receiving routine antenatal care in a two-partner training practice in south Manchester were offered carrier testing for cystic fibrosis using a computer protocol for antenatal care developed by the practice. A questionnaire including a Spielberger state-trait anxiety inventory was sent to patients 2 weeks after they received the results of their carrier test, and interviews with the patients in their home were carried out 4 weeks and one year after they received the result. RESULTS: All but one patient (75 out of 76) booking before 14 weeks of pregnancy accepted the offer of cystic fibrosis carrier testing, and 96% (72 out of 75) felt that they had made the right decision and that they had enough time for discussion with their general practitioner before testing. CONCLUSIONS: Cystic fibrosis carrier testing can be successfully integrated into the antenatal booking appointment in general practice and is acceptable to patients. This is a model for other genetic screening opportunities resulting from advances in medical genetics.     

紧密连锁的多态性位点在β地中海贫血植入前遗传学诊断中的应用

目的 探讨与β珠蛋白基因紧密连锁的多态性位点HumTH01在β地中海贫血（β地贫）植入前遗传学诊断（preimplantation genetic diagnosis，PGD）中的作用。方法 对4例已出生重型β地贫患儿的、双方均为β地贫基因携带者的夫妇进行了6个周期的PGD治疗，应用多重巢式PCR同时检测β珠蛋白基因及HumTH01基因，选择健康的胚胎移植入子宫。结果 6个周期共活检44个胚胎，获得44个卵裂球，其中41个卵裂球扩增成功，35个胚胎经PCR分析后获得明确诊断，移植了14个胚胎，获得1例临床妊娠。孕17周时经脐带血穿刺，证实为完全正常胚胎，现已出生一正常女婴。单个卵裂球平均扩增效率为89．7％，等位基因脱扣（allele drop-out，ADO）率为14．4％。HumTH01基因可以帮助检测出ADO及污染的发生。结论 本研究为国内首次报道应用多重巢式PCR同时检测β珠蛋白基因及HumTH01基因对β地贫进行植入前遗传学诊断并成功获得临床妊娠。在PGD中同时检测与β珠蛋白基因紧密连锁的多态性位点可以降低PGD中由于ADO及污染造成的误诊的风险。     

The uptake and acceptability to patients of cystic fibrosis carrier testing offered in pregnancy by the GP.

OBJECTIVE: To determine the uptake and acceptability of cystic fibrosis (CF) carrier testing when offered to women at the first antenatal booking appointment by their general practitioner. SETTING: Eight-general practices in the north west region with a combined patient list size of 42000. DESIGN: Offer of carrier screening at first antenatal booking appointment to pregnant women below 14 weeks' gestation; women accepting were alternately allocated to either couple testing (with full disclosure) or stepwise testing: SUBJECTS: Six hundred and twenty three women were offered CF carrier testing. MAIN OUTCOME MEASURES: (1) Acceptance of the offer of CF carrier testing. (2) Acceptability of the test to women following screening, evaluated through (i) postal questionnaire, (ii) semistructured interview. RESULTS: Five hundred and twenty-nine (84.9%) women accepted the test; the level of uptake varied across the eight practices (range 11-99%). In 26/249 (10%) couple tests no paternal sample was provided. When asked what had influenced their decision to be tested, 59/377 (16%) women did not refer to CF in their answers and six (2%) said that they did not feel they could refuse the test. After receiving their results, 368/379 (97%) women felt that they had made the right decision to be tested, but two carriers and three non-carriers had felt unhappy about testing. Couple testing with full disclosure was associated with lower anxiety levels two weeks after receiving the result for the pregnancy than stepwise testing and 82/278 (29%) non-carriers believed that they had no residual risk in relation to CF. CONCLUSIONS: The response from women accepting CF carrier testing was largely positive but a minority of women expressed concern about the test and the way it was offered and a substantial proportion of women were falsely reassured by their "negative" result. Higher levels of acceptance tended to occur in the practices which offered the test there and then rather than giving couples more time to decide about testing. Some women appeared to have accepted the test because of a belief in the importance of testing in pregnancy rather than because of the disease in question.     

Fetal hydrops in Sardinia: implications for genetic counselling

This paper describes the first case of Hb Bart's hydrops fetalis syndrome in the Sardinian population. Despite the high frequency of a-thalassemia, fetal hydrops is extraordinarily rare in the Sardinian population because a-thalassemia is more usually the result of the single a-thalassemia globin gene deletion and is very rarely produced by the deletion of two a-globin genes. The fetus, the product of a consanguineous marriage at risk for beta-thalassemia, was monitored by chorionic villi DNA analysis which detected the heterozygous state for the codon 39 nonsense mutation. Follow-up ultrasound examination showed fetal hydrops, which led us to carry out further investigation. Hemoglobin and a-globin gene analysis on cord blood obtained by cordocentesis revealed the homozygous state for the most common deletion ao-thalassemia in Mediterranean populations. Retrospective evaluation of the father's hematological features showed very low MCH-MCV for a beta-thalassemia carrier which may indicate co-inherited a-thalassemia. These findings indicate that careful evaluation of red cell indices of parents at risk for beta-thalassemia and adequate consideration of the consanguinity may point to co-inherited a-thalassemia and lead to the appropriate analysis.     

应用全基因组扩增技术对β-地中海贫血进行胚胎植入前遗传学诊断

目的 探讨对β-地中海贫血进行胚胎植入前遗传学诊断的方法。方法 夫妇双方分别为β41-42(-TCTT)及IVS-I 654(C→T)突变杂合子，在本中心进行体外受精-胚胎移植和胚胎植入前遗传学诊断。结果 13个胚胎中共有11个胚胎经PCR分析后获得明确诊断，正常胚胎2个(18．1％)；杂合子胚胎6个(54．5％)；双重杂合子胚胎3个(27．3％)。共移植3个胚胎，其中2个正常胚胎、1个杂合子胚胎。在胚胎移植后5周B超示三胎妊娠，孕8周自然减一胎，并于孕20周时经产前诊断，证实均为健康胎儿。现已分娩双胎分别为正常和杂合子。结论 成功应用全基因组扩增技术对β-地中海贫血进行胚胎植入前遗传学诊断，并分娩健康双胎。     

The impact of population based screening for carriers of cystic fibrosis.

The purpose of the study was to evaluate the short-term effects of population based screening for carriers of cystic fibrosis. The outcome measures included perceptions of health, anxiety, and understanding of test results. Those adults aged between 18 and 45, registered with a general practice in Inner London, who accepted the offer of carrier testing, completed questionnaires before testing, upon receipt of results, and three months later. Full data were obtained from 427 with negative test results and 14 carriers. Receipt of results had no effect upon perceptions of health or perceived risk of having an abnormal baby. Those receiving a positive test result were significantly more anxious upon receipt of this result. By three months, this anxiety had dissipated. While knowledge of the test improved from before to after testing, by three months there was some decay. Although the residual risk among those with a negative result of being a carrier was given as 1:135, at least 17% of those receiving a negative result incorrectly believed that they were at no risk of having a child with cystic fibrosis. Five of the 14 receiving a positive result erroneously believed that their results meant that they probably, but not definitely, carried the gene for cystic fibrosis. In the longer term the greatest problem of population screening would appear to be one of false reassurance rather than anxiety. Longer term studies are needed to determine how well carrier status information is retained, and how carriers and carrier couples plan and respond to pregnancy and how much understanding they retain of their test results.     

Rapid detection of beta-globin gene (HBB) mutations coupling heteroduplex and primer-extension analysis by DHPLC

Beta-thalassemia is a common inherited disease, resulting from one or more of a total of more than 200 different mutations in the beta-globin gene (HBB). Efficient and reliable mutation-screening methods are essential in order to establish appropriate prevention programs for at-risk populations based upon a molecular diagnosis. We have developed a rapid and highly-specific mutation screening test for the diagnosis of beta-thalassemia by coupling heteroduplex and primer-extension analysis based on the denaturing high performance liquid chromatography (DHPLC) system. A total of 161 healthy heterozygous Taiwanese carriers featuring 10 different HBB mutations and 30 patients exhibiting 12 different compound heterozygous or homozygous HBB mutations were subjected to DHPLC. The elution profile for the heteroduplex analysis of DHPLC could be successfully used to identify the common disease-causing mutations of HBB. To further confirm the sequence variants, we developed a technique combining multiplex primer-extension analysis coupled with DHPLC for the genotyping of eight common disease-causing mutations in the HBB gene. Overall, by coupling heteroduplex and primer-extension analysis based upon DHPLC, we were able to unambiguously identify the most-common beta-thalassemia mutations corresponding to more than 99% of HBB alleles among the Taiwanese population. In conclusion, compared to classic approaches to mutation screening for this malady, we suggest that DHPLC is an excellent technique to be applied to the genetic screening of prenatal and postnatal individuals as a part of a diagnosis program for beta-thalassemia and provides a more-efficient, economic, and sensitive means to undertake such a screening program.     

The influence of genetic counselling in the era of DNA testing on knowledge, reproductive intentions and psychological wellbeing

Subjects of reproductive age at risk of having an affected child with a severe single gene disorder such as Duchenne muscular dystrophy (DMD) or cystic fibrosis (CF) were surveyed to ascertain: their views on genetic counselling and antenatal testing; their knowledge of their risk of having an affected child; and their psychological wellbeing. Questionnaires were posted to 209 individuals at 130 addresses; a 65% response rate was achieved. The majority of those surveyed were under 40 years of age (91%), half of them had received genetic counselling only once and for 47% the first encounter was after the diagnosis of their affected child. Most patients expressed their intention to use prenatal testing. However, less than 50% of those counselled knew their risk of having an affected child. Knowledge of risk was associated with the type of disease in the family (p<0.001) (inheritance of DMD was poorly understood by relevant subjects) and was positively associated with the participant's level of education (p<0.05). We did not detect a significant association between the number of intended children and the risk of having an affected child. In terms of family relations, genetic counselling appears to be beneficial for the nuclear family, the couple and their children, but some counsellees reported a detericration in relations with other relatives. The results indicate that couples at risk of having a child with a severe genetic disorder value the counselling provided, but many of them do not remember important facts in relation to their risk status.     

Real-time PCR for single-cell genotyping in sickle cell and thalassemia syndromes as a rapid, accurate, reliable, and widely applicable protocol for preimplantation genetic diagnosis

Sickle-cell and beta-thalassemia syndromes are priority genetic diseases for prevention programs involving population screening with the option of prenatal diagnosis for carrier couples. Preimplantation genetic diagnosis (PGD) represents a specialized alternative to prenatal diagnosis and is most appropriately used for couples with an unsuccessful reproductive history and/or undergoing assisted reproduction. However, clinical application of PGD has been hindered by difficulties in reliably transferring molecular diagnostic protocols to the single-cell level. We standardized and validated a protocol involving first-round multiplex PCR, amplifying the region of the beta-globin gene containing most of the common disease mutations world-wide and two unlinked microsatellite markers (GABRB3 and D13S314), followed by: 1) analysis of beta-globin genotypes with real-time PCR and 2) microsatellite sizing to exclude chance contamination. The protocol was standardized on 100 single lymphocytes from a beta-thalassemia heterozygote, including 15 artificially contaminated samples, the latter demonstrated through microsatellite analysis. PCR failure and allele drop-out (ADO) were observed in one (uncontaminated) sample each (1.2%). A pilot study in six clinical PGD cycles with five different beta-globin genotype interactions achieved results (in 5-6 hr) in 46 out of 50 single blastomeres (92%), all concordant with results from an established PGD method applied simultaneously; microsatellite analysis detected only parental alleles, excluding contamination. Beta-globin genotypes were also confirmed in two blastomeres through prenatal diagnosis (twin pregnancy), and in 11 out of 12 spare embryos, revealing one incident of ADO. Overall, the protocol proved to be sensitive, accurate, reliable, rapid, and applicable for many genotype interactions, with internal monitoring of contamination, thus fulfilling all requirements for clinical PGD application.