Ten years' experience of antenatal mean corpuscular volume screening and prenatal diagnosis for thalassaemias in Hong Kong

Comprehensive analysis of recessive carrier status using exome and genome sequencing data in 1543 Southern Chinese

Traditional carrier screening has been utilized for the detection of carriers of genetic disorders. Since a comprehensive assessment of the carrier frequencies of recessive conditions in the Southern Chinese population is not yet available, we performed a secondary analysis on the spectrum and carrier status for 315 genes causing autosomal recessive disorders in 1543 Southern Chinese individuals with next-generation sequencing data, 1116 with exome sequencing and 427 with genome sequencing data. Our data revealed that 1 in 2 people (47.8% of the population) was a carrier for one or more recessive conditions, and 1 in 12 individuals (8.30% of the population) was a carrier for treatable inherited conditions. In alignment with current American College of Obstetricians and Gynecologists (ACOG) pan-ethnic carrier recommendations, 1 in 26 individuals were identified as carriers of cystic fibrosis, thalassemia, and spinal muscular atrophy in the Southern Chinese population. When the >1% expanded carrier screening rate recommendation by ACOG was used, 11 diseases were found to meet the criteria in the Southern Chinese population. Approximately 1 in 3 individuals (35.5% of the population) were carriers of these 11 conditions. If the 1 in 200 carrier frequency threshold is used, and additional seven genes would meet the criteria, and 2 in 5 individuals (38.7% of the population) would be detected as a carrier. This study provides a comprehensive catalogue of the carrier spectrum and frequency in the Southern Chinese population and can serve as a reference for careful evaluation of the conditions to be included in expanded carrier screening for Southern Chinese people.

Optimal cutoff of mean corpuscular volume (MCV) for screening of alpha-thalassemia 1 trait

AIM

To identify the optimal cutoff of mean corpuscular volume (MCV) for screening of alpha-thalassemia 1 trait.

METHODS

The database of pregnant women who attended antenatal care clinic at Department of Obstetrics and Gynecology, Chiang Mai University during January 1st, 2015 to December 31st, 2017 was accessed and reviewed. A total of 1264 cases who had MCV ≤80 fL and met the inclusion criteria were enrolled to the study. Cases with hemoglobin level ≤10.0 gm/dL, iron deficiency anemia, chronic medical diseases and other types of thalassemia trait except alpha-thalassemia 1 trait were excluded.

RESULTS

After exclusion, 438 cases were available for analysis. Of them, 139 were alpha-thalassemia 1 trait. Based on the receiver operating characteristic curves, the best cutoff value of MCV for screening of alpha-thalassemia 1 trait was ≤76.15 fL, giving 100% sensitivity, and 60.9% specificity with the area under curve of 0.925. Compared to the conventional cutoff (≤80 fL), the new cutoff gave much less false positive tests (117 vs 299 cases), whereas capability to detect alpha-thalassemia 1 trait was the same.

CONCLUSION

With the new MCV cutoff (≤76.15 fL) as a secondary cutoff for screening alpha-thalassemia 1 carrier, a substantial number of positive cases requiring DNA analysis could be avoided without compromising the detection efficacy.

The ‑α3.7 deletion in α‑globin genes increases the concentration of fetal hemoglobin and hemoglobin A2 in a Saudi Arabian population

The regions of Al‑Qatif and Al‑Ahssa in the Eastern Province of Saudi Arabia are known for their high prevalence of hemoglobinopathies, including β‑thalassemia and sickle cell anemia. Previously, the α‑gene deletion has been demonstrated as highly prevalent among populations residing in these two regions. The present study was conducted in order to investigate the implications of the α‑globin gene deletion on fetal hemoglobin (HbF) and hemoglobin α2 (HbA2) concentrations in patients with transfusion‑dependent β‑thalassemia. A total of 166 Saudi patients with transfusion‑dependent β‑thalassemia and 337 healthy Saudi patients were included in the study. The ‑α3.7, ‑α4.2, -‑FIL, -‑SEA, -‑MED and -‑(20.5) gene deletions were identified using multiplex α‑globin deletion polymerase chain reaction. The present study revealed that the ‑α3.7 gene deletion is the most prevalent (43.5%) in the Saudi populations that were analyzed and is characterized by the deletion of 3,804 base pairs. Numerous genotypes, namely ‑3.7α2/α1α2, ‑3.7α2/α1α12, ‑3.7α2/‑3.7α2, ‑3.7α2HphI/α1α2HphI, ‑3.7α2/α1‑4.2, ‑3.7α2/α1polyA‑1α2, ‑3.7α12/α1α12, ‑‑FIL/‑3.7α2 and ‑3.7α2/‑3.7α2Hb Villiers le Bel were also identified in the investigated population. Furthermore, a gradual increase in the concentration of HbF and HbA2 in patients with β‑thalassemia and the number of α‑gene deletions was demonstrated; whereas in healthy patients the level of HbA2 was demonstrated to decrease as the number of α‑gene deletions increased. Therefore, it can be concluded that the high HbF concentration in the present study is predominantly associated with other mutations associated with β‑thalassemia rather than α‑globin deletions. Furthermore, the results of the present study also revealed novel α‑gene deletion genotypes prevalent in the population studied, namely α1α2/α1α2HphI, α1α2HphI/α1α2HphI, α1α2/α1α2Hb Handsworth, ‑3.7α2HphI/α1α2HphI, ‑3.7α2/‑3.7α2Hb Villiers le Bel and ‑-MED/α1α2HphI.

An international registry of survivors with Hb Bart's hydrops fetalis syndrome

Hemoglobin (Hb) Bart's hydrops fetalis syndrome (BHFS) resulting from α0-thalassemia is considered a universally fatal disorder. However, over the last 3 decades, improvements in intrauterine interventions and perinatal intensive care have resulted in increasing numbers of BHFS survivors. We have initiated an international registry containing information on 69 patients, of which 31 are previously unpublished. In this perspective, we analyze the available clinical information to document the natural history of BHFS. In the future, once we have accrued sufficient cases, we aim to build on this study and provide information to allow counseling of at-risk couples. To date, 39 patients have survived beyond the age of 5 years, 18 of whom are now older than 10 years. Based on the available cases, we find evidence to suggest that intrauterine therapy provides benefits during the perinatal and neonatal period; however, it may not provide additional benefits to long-term growth and neurodevelopmental outcomes. Growth retardation is a major adverse long-term outcome among BHFS patients with ∼40% being severely affected in terms of weight and ∼50% in terms of height. There is also an increased risk of neurodevelopmental delay as we find 20% (11/55) of BHFS survivors suffer from a serious delay of ≥6 months. Most patients in the registry require lifelong transfusion and often have associated congenital abnormalities and comorbidities. This perspective is a first step in gathering information to allow provision of informed counseling on the predicted outcomes of affected babies.

Role of red cell distribution width in screening for Hb E trait in population screening for hemoglobin disorders

The national screening policy for hemoglobinopathies uses the cutoffs for red cell indices mean corpuscular volume >80 and mean corpuscular hemoglobin >27, a strategy known to miss some individuals with Hb E trait (EBT), the most common abnormal hemoglobin in Sri Lanka. We wanted to determine if red cell distribution width (RDW) cutoff values would help in increasing the sensitivity of screening for Hb E trait. High-performance liquid chromatography was carried out as the gold standard to detect hemoglobinopathies and red blood cell parameters with colter counter. Receiver operating characteristic curve was drawn to determine the cutoff value for EBT against β-trait (BTT) and other anemias. Of the 504 patients, 246 had BTT, 110 had EBT, and 151 had other types of anemias. Mean (SD) RDW among patients with BTT was 16 (2.8), with EBT 14.5 (2.9), and with other anemias 15.8 (4.2) (P>0.001). With 14.45 as the cutoff for RDW and considering accepted values for mean corpuscular volume >80 and mean corpuscular hemoglobin >27, it gave a predictive sensitivity of 98.2% for EBT. By using RDW cutoff at 14.45 in addition to the accepted screening indices, sensitivity of Hb E trait detection went up to 98.2% from 86.6%. This study highlights the importance of taking RDW into consideration for screening.

Advances in detection of hemoglobinopathies

Hemoglobin disorders are recognized as one of the most common inherited diseases worldwide. Detecting and characterizing variant hemoglobins and thalassemias depends primarily on clinical laboratory methods. Multiple biophysical, biochemical, and genetic assays are available to provide phenotypic or genotypic evidence of pathology. For many years conventional slab-gel electrophoresis and HPLC were the most commonly utilized laboratory methods. However, the field has rapidly expanded to regularly include capillary zone electrophoresis, molecular assays, and, more recently, mass spectrometric assays. Interpretation of these techniques is, in general, complicated because of the involvement of multiple polymorphic genes. Proper characterization of hemoglobin variants is necessary for diagnosis, primary prevention and genetic counseling for underlying disorders. This review provides an overview of the current hemoglobin analysis techniques, and also discusses technologies that have potential to translate into widespread clinical settings.

Distribution of alpha thalassaemia gene variants in diverse ethnic populations in malaysia: data from the institute for medical research

Alpha thalassaemia is highly prevalent in the plural society of Malaysia and is a public health problem. Haematological and molecular data from 5016 unrelated patients referred from various hospitals to the Institute for Medical Research for α thalassaemia screening from 2007 to 2010 were retrieved. The aims of this retrospective analysis were to describe the distribution of various alpha thalassaemia alleles in different ethnic groups, along with their genotypic interactions, and to illustrate the haematological changes associated with each phenotype. Amongst the patients, 51.2% (n = 2567) were diagnosed with α thalassaemia. Of the 13 α thalassaemia determinants screened, eight different deletions and mutations were demonstrated: three double gene deletions, --(SEA), --(THAI), --(FIL); two single-gene deletions, α-³·⁷ and -α⁴·²; and three non-deletion mutations, Cd59G > A (haemoglobin [Hb] Adana), Cd125T > C (Hb Quong Sze) and Cd142 (Hb Constant Spring). A high incidence of α-³·⁷ deletion was observed in Malays, Indians, Sabahans, Sarawakians and Orang Asli people. However, the --SEA deletion was the most common cause of alpha thalassaemia in Chinese, followed by the α-³·⁷ deletion. As many as 27 genotypic interactions showed 1023 α thalassaemia silent carriers, 196 homozygous α⁺ thalassaemia traits, 973 heterozygous α⁰ thalassaemia carriers and 375 patients with Hb H disease. Statistical analysis showed a significant difference in the distribution of α thalassaemia determinants amongst the various ethnic groups. Hence, the heterogeneous distribution of common determinants indicated that the introduction of an ethnicity-targeted hierarchical α thalassaemia screening approach in this multi-ethnic Malaysian population would be effective.

Carrier Testing for Autosomal- Recessive Disorders

The aim of carrier testing is to identify carrier couples at risk of having offspring with a serious genetic (autosomal recessive) disorder. Carrier couples are offered genetic consultation where their reproductive options, including prenatal diagnosis, are explained. The Ashkenazi Jewish population is at increased risk for several recessively inherited disorders (Tay-Sachs disease, Cystic fibrosis, Canavan disease, Gaucher disease, Familial Dysautonomia, Niemann-Pick disease, Fanconi anemia, and Bloom syndrome). Unlike Tay-Sachs disease, there is no simple biochemical or enzymatic test to detect carriers for these other disorders. However, with the rapid identification of disease-causing genes in recent years, DNA-based assays are increasingly available for carrier detection. Approximately 5% of the world's population carries a mutation affecting the globin chains of the hemoglobin molecule. Among the most common of these disorders are the thalassemias. The global birth rate of affected infants is at least 2 per 1000 (in unscreened populations), with the greatest incidence in Southeast Asian, Indian, Mediterranean, and Middle Eastern ethnic groups. Carriers are detected by evaluation of red cell indices and morphology, followed by more sophisticated hematological testing and molecular analyses. The following issues need to be considered in the development of a carrier screening program: (1) test selection based on disease severity and test accuracy; (2) funding for testing and genetic counselling; (3) definition of the target population to be screened; (4) development of a public and professional education program; (5) informed consent for screening; and (6) awareness of community needs.

Alpha-thalassaemia

Alpha-thalassaemia is one of the most common human genetic disorders. Couples in which both partners carry alpha(0)-thalassaemia traits have a 25% risk of having a fetus affected by homozygous alpha-thalassaemia or haemoglobin Bart's disease, with severe fetal anaemia in utero, hydrops fetalis, stillbirth or early neonatal death, as well as causing various maternal morbidities. This disorder is common in southeast Asia and southern China, and the expanding populations of southeast Asian immigrants in the US, Canada, UK and Europe mean that this disorder is no longer rare in these countries.

Full karyotyping, rapid aneuploidy diagnosis or both when invasive prenatal testing is performed for diagnosis of thalassaemia?

A retrospective study was performed to compare the detection rate of chromosomal abnormalities by different approaches of full karyotyping, rapid aneuploidy diagnosis (RAD) or both when invasive prenatal testing is performed for diagnosis of thalassaemia. The karyotype results of 1120 prenatal samples obtained from thalassaemia couples from January 1985 to December 2002 in a referral centre for prenatal diagnosis were studied. The detection rate of chromosomal abnormalities by four different approaches were compared: (i) karyotyping for all samples; (ii) RAD (21,18,13,X,Y) for all samples; (iii) RAD for all samples + karyotyping for cases with ultrasound abnormalities; and (iv) RAD (21,18,13) for all + RAD (X,Y) for cases with ultrasound abnormalities consistent with Turner syndrome + karyotyping for cases with ultrasound abnormalities. Normal karyotypes were found in 1103 samples (98.5%). There were 17 cases (1.5%) of chromosomal abnormalities: four cases (0.36%) were clinically significant, eight cases (0.7%) were of borderline clinical significance and five cases (0.44%) were not confirmed by subsequent prenatal or postnatal tests. The incidences of autosomal (7/1120 = 0.63%) and sex chromosomal (5/1120 = 0.45%) abnormalities were not higher than those (0.41 and 0.22%, respectively) from newborn surveys (Hook and Hamerton, 1977) (P = 0.398 and 0.216, respectively). Approach 1 would detect all 17 chromosomal abnormalities. Approach 2 would detect three of four clinically significant chromosomal abnormalities but not detect six of eight chromosomal abnormalities of borderline clinical significance and three of five chromosomal abnormalities not confirmed by subsequent prenatal or postnatal tests. Approach 3, in addition, would be able to detect all four clinically significant chromosomal abnormalities. Approach 4 would detect all four clinically significant chromosomal abnormalities but would not detect seven of eight chromosomal abnormalities of borderline clinical significance and four of five chromosomal abnormalities not confirmed by subsequent prenatal or postnatal tests. RAD (21,18,13) for all + RAD (X,Y) for cases with ultrasound abnormalities consistent with Turner syndrome + karyotyping for cases with ultrasound abnormalities seemed to be the best approach for the detection of chromosomal abnormalities when invasive prenatal testing is performed for diagnosis of thalassaemia.

Heterogeneity in alpha-thalassemia interactions in Malays, Chinese and Indians in Malaysia

AIM

Interactions between different determinants of alpha-thalassemia raises considerable problems, particularly during pregnancies where antenatal diagnosis is necessary. This study aims to determine the different types of deletional alpha-thalassemia and Hemoglobin Constant Spring (HbCS), and their frequency in Malays, Chinese and Indians in Malaysia.

METHODS

DNA from 650 pregnant women from the Antenatal Clinic of the University of Malaya Medical Center in Kuala Lumpur, Malaysia who showed mean cell volume < or =89 fL and/or mean cell hemoglobin < or =28 pg were analyzed for the double alpha-globin gene South-East Asian deletion (--SEA), the -alpha3.7 and -alpha4.2 single alpha-globin gene deletions and HbCS.

RESULTS

One hundred and three (15.8%) of the pregnant women were confirmed as alpha-thalassemia carriers: 25 (3.8%) were alpha-thalassemia-1 carriers with the --SEA/alphaalpha genotype, 64 (9.8%) were heterozygous for the -alpha3.7 rightward deletion (-alpha3.7/alphaalpha), four (0.6%) were heterozygous for the -alpha4.2 leftward deletion (-alpha4.2/alphaalpha), nine (1.4%) were heterozygous for HbCS (alphaCSalpha/alphaalpha) and one (0.2%) was compound heterozygous with the -alpha3.7/alphaCSalpha genotype. The double alpha-globin gene --SEA deletion was significantly higher in the Chinese (15%) compared to the Malays (2.5%) and not detected in the Indians studied. The -alpha3.7 deletion was distributed equally in the three races. HbCS and -alpha4.2 was observed only in the Malays.

CONCLUSION

The data obtained gives a better understanding of the interactions of the different alpha-thalassemia determinants in the different ethnic groups, thus enabling more rapid and specific confirmation of alpha-thalassemia in affected pregnancies where antenatal diagnosis is necessary.

Thalassaemia screening in pregnancy

PURPOSE OF REVIEW

This review provide an update on antenatal screening and diagnosis of thalassaemia disorders.

RECENT FINDINGS

The topics covered are the effectiveness of antenatal screening programmes for thalassaemia, its prenatal diagnosis, molecular basis and laboratory findings, ultrasound screening for haemoglobin Bart's disease, and non-invasive prenatal diagnosis of thalassaemia.

SUMMARY

Universal antenatal screening for thalassaemia carriers should be implemented in populations with a high prevalence of this condition. The appropriate measure to screen for alpha and beta thalassaemias remains mean cell haemoglobin (<27 pg) or mean corpuscular volume (<80 fl). A haemoglobin pattern and iron profile should follow if the red cell indices are low. In a population where alpha thalassaemia is prevalent, it is advisable to check the partner's mean cell haemoglobin or mean corpuscular volume as well. Further cascades of investigations will depend on these results and the prevalence of other haemoglobinopathies in that population. Invasive prenatal diagnosis remains the gold standard for diagnosis in high-risk couples. Provided expertise is available, ultrasound measurement of the cardiothoracic ratio appears a good screening tool for alpha thalassaemia major. Non-invasive prenatal diagnosis by identification of a paternal mutation in maternal plasma, although currently at the experimental stage, may be an option in the future.

Cost-effectiveness of prenatal screening for thalassaemia in Hong Kong

OBJECTIVES

To determine the cost effectiveness of a universal prenatal screening program for alpha- and beta-thalassaemia.

METHODS

We retrospectively reviewed our program from 1998 to 2002, and calculated the direct and indirect costs of various components.

RESULTS

18,936 women were screened at our prenatal clinic and 153 couples were subsequently referred to our Prenatal Diagnostic Centre for counselling and further investigations. In addition, there were 238 tertiary referrals and 157 self-referrals. After investigations, 84 fetuses were at risk of beta-thalassaemia major/beta-E thalassaemia, 19 of them were affected and 18 were aborted. The total expenditure on our program (HK 10.0 million dollars) would be less than the postnatal service costs (HK 40.4 million dollars) for 18beta-thalassaemia major fetuses if they were born. Of 361 women at risk of carrying a homozygous alpha0-thalassaemia fetus, 311 (86.2%) opted for the indirect approach (using serial ultrasound examinations to exclude Hb Bart's disease), and 76 (24.5%) subsequently underwent an invasive test for a definitive diagnosis. The sensitivity and false positive rate of this indirect approach was 100.0% and 2.9% respectively.

CONCLUSION

It is cost effective to run a universal prenatal screening program in an area where both beta-thalassaemia and alpha-thalassaemia are prevalent. The indirect approach can effectively avoid an invasive test in unaffected pregnancies.