Antenatal diagnosis of beta-thalassemia by isoelectric focusing in immobilized ph gradients

Diagnostic utility of isoelectric focusing and high performance liquid chromatography in neonatal cord blood screening for thalassemia and non-sickling hemoglobinopathies

BACKGROUND

Thalassemia syndromes are highly prevalent in Southeast Asia. In Thailand, high performance liquid chromatography (HPLC) is the most common technique routinely performed in diagnosis of thalassemia and hemoglobinopathies, while isoelectric focusing (IEF) is rarely employed. We compared the diagnostic utility of IEF and HPLC in neonatal screening for thalassemia and non-sickling hemoglobinopathies.

METHODS

Two-hundred and forty-one cord blood samples were analyzed using IEF and HPLC, β-thalassemia short program. The results were correlated with red cell indices and molecular analyses. Hemoglobin (Hb) Bart's was quantified only on IEF.

RESULTS

Of 241 newborns, IEF and HPLC yielded 85.4% and 76.4% sensitivity to identify α-thalassemia syndrome, respectively. HbBart's≥2% yielded 100% sensitivity to identify 2 α-globin gene deletions and/or mutations, while MCV≤95fl and MCH≤30pg yielded 100% sensitivity to identify 2 α-globin gene deletions. DNA analysis revealed HbE mutation in all 61 subjects with HbA2>1% on both IEF and HPLC.

CONCLUSION

IEF is an effective method in neonatal screening for thalassemia and non-sickling hemoglobinopathies. The HbBart's level, MCV and MCH are helpful for identifying α-thalassemia. The presence of HbA2 higher than 1% in cord blood indicates HbE carriers in Southeast Asian newborns.

Diagnostic applications of newborn screening for α-thalassaemias, haemoglobins E and H disorders using isoelectric focusing on dry blood spots

Background

Neonatal screening for haemoglobin (Hb) disorders is a standard of care in several developed countries with the main objective to detect Hb S. Such practice has not been established in Thailand where α-thalassaemia and haemoglobin E (Hb E) are highly prevalent. Early identification of thalassaemias could be helpful and strengthen the programme for prevention and control for severe thalassaemias.

Methods

Data from isoelectric focusing (IEF) and Isoscan® for detecting types and amount (%) of each haemoglobin in 350 newborn’s dried blood spots were analysed and compared with the comprehensive genotype analysis by DNA studies as a gold standard.

Results

Based on genetic profiles, there were 10 different categories: (1) normal ( n = 227), (2) α+-thalassaemia trait ( n = 14), (3) α0-thalassaemia trait ( n = 13), (4) β0-thalassaemia trait ( n = 7), (5) Hb E trait ( n = 72), (6) Hb E trait with α0-thalassaemia or homozygous α+-thalassaemia ( n = 5), (7) Hb E trait with α+-thalassaemia trait ( n = 5), (8) homozygous Hb E ( n = 3), (9) homozygous Hb E with α0-thalassaemia trait ( n = 1) and (10) Hb H disease ( n = 3). The presence of Hb Bart’s and Hb E were used to identify cases with α-thalassaemia and Hb E, respectively. We set 0.25% of Hb Bart’s and 1.5% of Hb E as a cut-off level to detect α+-thalassaemia trait (sensitivity 92.86% and specificity 74.0%) and Hb E trait with 100% of both sensitivity and specificity for IEF diagnosis.

Conclusion

Although molecular diagnosis seems to be better for definitive diagnosis of thalassaemia syndromes at birth, however, using our reference range described herein, IEF can be applied in a resource-limiting setting with acceptable reliability.

Increased prevalence of false positive hemoglobinopathy newborn screening in premature infants

BACKGROUND

The objective was to investigate the specificity of the hemoglobinopathy newborn screening in premature neonates as compared to term neonates.

PROCEDURE

The screening results from infants suspected to have hemoglobinopathy disease identified by the Florida Newborn Screening Program for years 2002-2007 were compared to the corresponding confirmatory testing. The risks for false positives for preterm and full term newborns were calculated by Chi-square or the Cochran-Armitage test for trend. Isoelectric focusing and HPLC were the methods of hemoglobin screening.

RESULTS

Over 2,300 neonates (1/576 neonates born in Florida) were suspected to have hemoglobinopathy. The most common abnormal pattern in term and preterm infants (gestational age 22-36 weeks) suggesting disease at screening was FS. Overall, 93% of the children who screened positive for FCA and 64% of infants identified with FSA were later confirmed with trait. FSC was confirmed in 96% of the cases in both preterm and term infants. Compared to term newborns, preterm newborns were more likely to have a false positive result for FS or FC at screening. Twenty-three percent of preterms with FS and 59% of preterms with FC were diagnosed as traits by confirmatory testing, compared to only 2% and 6% for term infants (P < 0.001).

CONCLUSIONS

As compared to term newborns, more preterm newborns with trait were misidentified as having sickle cell anemia or hemoglobin C at screening. We speculate that abnormal hemoglobins may precede the development of hemoglobin A during fetal life.

Molecular diagnosis of inherited disorders: lessons from hemoglobinopathies

Hemoglobinopathies constitute a major health problem worldwide, with a high carrier frequency, particularly in certain regions where malaria has been endemic. These disorders are characterized by a vast clinical and hematological phenotypic heterogeneity. Over 1,200 different genetic alterations that affect the DNA sequence of the human alpha-like (HBZ, HBA2, HBA1, and HBQ1) and beta-like (HBE1, HBG2, HBG1, HBD, and HBB) globin genes are mainly responsible for the observed clinical heterogeneity. These mutations, together with detailed information about the resulting phenotype, are documented in the globin locus-specific HbVar database. Family studies and comprehensive hematological analyses provide useful insights for accurately diagnosing thalassemia at the DNA level. For this purpose, numerous techniques can provide accurate, rapid, and cost-effective identification of the underlying genetic defect in affected individuals. The aim of this article is to review the diverse methodological and technical platforms available for the molecular diagnosis of inherited disorders, using thalassemia and hemoglobinopathies as a model. This article also attempts to shed light on issues closely related to thalassemia diagnostics, such as prenatal and preimplantation genetic diagnoses and genetic counseling, for better-quality disease management.

Isoelectric focusing in immobilized pH gradients: applications in clinical chemistry and forensic analysis

The applications of isoelectric focusing in immobilized pH gradients in clinical chemistry and forensic analysis are reviewed. Strong emphasis is given to the separation of serum proteins, in particular alpha 1-acidic glycoprotein, acid phosphatase, alkaline phosphatase, alpha 1-antitrypsin, apolipoproteins, complement component, factor B, factor XIIIB, group-specific component, lecithin:cholesterol acyltransferase, phosphoglucomutase, prealbumin, protein C and transferrin. The analysis of human parotid salivary proteins is discussed and an assessment is given of the state of the art in thalassaemia screening.

DNA polymorphism and globin chain analysis in the prenatal diagnosis of beta-thalassaemia major in Taiwan

Thirty-six pregnancies in 25 families at risk of beta-thalassaemia major received prenatal diagnosis. Chorionic villus sampling or amniocentesis was done in 35 pregnancies to obtain fetal cells for DNA linkage study, for which Southern blotting and DNA hybridization were used to detect seven restriction fragment length polymorphisms (RFLPs) within the beta-globin gene cluster: epsilon-HincII, G gamma-HindIII, A gamma-HindIII, phi beta-HincII, 3' phi beta-HincII, beta-AvaII, and 3' beta-BamHI. beta-Thalassaemia major was diagnosed in seven and excluded in 22 pregnancies. In the remaining six cases, beta-thalassaemia major could not be excluded. In these six pregnancies and another one with late booking, ultrasound-guided cordocentesis was performed at the 22nd to 27th week of gestation. Globin chain composition was determined with urea-acetic acid-Triton X-100-12 per cent polyacrylamide gel electrophoresis. beta-Thalassaemia major was diagnosed in two fetuses and excluded in the other five. Eleven fetuses (in which beta-thalassaemia major was excluded) have been delivered and are healthy at more than 5 months old. DNA linkage analysis coupled with globin chain electrophoresis provides an effective way for prenatal diagnosis of beta-thalassaemia major, although these methods are being replaced by more direct detection techniques using oligonucleotide probes.

Rapid HPLC techniques for globin chain synthesis studies

Globin chain synthesis and alpha/beta ratios were determined in a number of normal subjects, alpha-thalassemia-2 homozygotes, and beta-thalassemia trait using three different techniques. Cation exchange high performance liquid chromatography on a Pharmacia Mono-S, HR 5/5 and reversed phase high performance liquid chromatography on a semi-preparative Vydac C4 column were compared with the traditional carboxymethylcellulose chromatography. Both high performance liquid chromatography columns give excellent results when 2 mg of hemoglobin was chromatographed in each analysis. By modifying the protocols for column equilibration and gradient shape for preparative Vydac C4 columns, conditions were found yielding excellent resolutions of the labeled globin chains in less than an hour without the need for substantial increase of the flowrate. This method was found to be superior to other methods and may be a suitable alternative for the classical carboxymethylcellulose chromatography. Up to five specimens could easily be analyzed in a single day with this system.

Prenatal diagnosis of hemoglobinopathies: a potential application of high performance liquid chromatography

High performance liquid chromatography was compared with carboxymethyl cellulose column chromatography data for analysis of globin chain composition and biosynthetic ratios in fetal blood. A formula was derived for mathematical correction for losses of small amounts of globin protein on the high performance liquid chromatography column. Radioactive globin chain ratios by high performance liquid chromatography are equivalent to those by carboxymethyl cellulose column chromatography, but only when carrier Hb A is added. We conclude that high performance liquid chromatography provides a suitable alternative to carboxymethyl cellulose columns, and has several advantages.