An improved method for detecting red cells with hemoglobin H inclusions that does not require glass capillary tubes

The role of molecular diagnostic testing for hemoglobinopathies and thalassemias

Hemoglobin disorders are among the most common genetic diseases worldwide. Molecular diagnosis is helpful in cases where the diagnosis is uncertain and for genetic counseling. Protein-based diagnostic techniques are frequently adequate for initial diagnosis. Molecular genetic testing is pursued in some cases, particularly when a definitive diagnosis is not possible and especially for the purpose of assessing genetic risk for couples wanting to have children. The expertise available in the clinical hematology laboratory is essential for the diagnosis of patients with hemoglobin abnormalities. Initial diagnoses are made using protein-based techniques such as electrophoresis and chromatography. Based on these findings, genetic risk to an individual's offspring can be assessed. In the setting of β-thalassemia and other β-globin disorders, coincident α-thalassemia may be difficult to diagnose, which can have potentially serious consequences. In addition, unusual forms of β-thalassemia caused by deletions in the β-globin locus cannot be definitively characterized using standard techniques. Molecular diagnostic testing has an important role in the diagnosis of hemoglobin disorders and is important in the setting of genetic counseling. Molecular testing also has a role in prenatal diagnosis to identify fetuses affected by severe hemoglobinopathies and thalassemias.

Molecular Diagnosis of Thalassemias and Hemoglobinopathies: An ACLPS Critical Review

OBJECTIVES

To describe the use of molecular diagnostic techniques for patients with hemoglobin disorders.

METHODS

A clinical scenario is presented in which molecular diagnosis is important for genetic counseling. Globin disorders, techniques for their diagnosis, and the role of molecular genetic testing in managing patients with these disorders are described in detail.

RESULTS

Hemoglobin disorders, including thalassemias and hemoglobinopathies, are among the commonest genetic diseases, and the clinical laboratory is essential for the diagnosis of patients with these abnormalities. Most disorders can be diagnosed with protein-based techniques such as electrophoresis and chromatography. Since severe syndromes can result due to inheritance of combinations of globin genetic disorders, genetic counseling is important to prevent adverse outcomes. Protein-based methods cannot always detect potentially serious thalassemia disorders; in particular, α-thalassemia may be masked in the presence of β-thalassemia. Deletional forms of β-thalassemia are also sometimes difficult to diagnose definitively with standard methods.

CONCLUSIONS

Molecular genetic testing serves an important role in identifying individuals carrying thalassemia traits that can cause adverse outcomes in offspring. Furthermore, prenatal genetic testing can identify fetuses with severe globin phenotypes.

Characterization of Deletions of the HBA and HBB Loci by Array Comparative Genomic Hybridization

Thalassemia is among the most common genetic diseases worldwide. α-Thalassemia is usually caused by deletion of one or more of the duplicated HBA genes on chromosome 16. In contrast, most β-thalassemia results from point mutations that decrease or eliminate expression of the HBB gene on chromosome 11. Deletions within the HBB locus result in thalassemia or hereditary persistence of fetal Hb. Although routine diagnostic testing cannot distinguish thalassemia deletions from point mutations, deletional hereditary persistence of fetal Hb is notable for having an elevated HbF level with a normal mean corpuscular volume. A small number of deletions accounts for most α-thalassemias; in contrast, there are no predominant HBB deletions causing β-thalassemia. To facilitate the identification and characterization of deletions of the HBA and HBB globin loci, we performed array-based comparative genomic hybridization using a custom oligonucleotide microarray. We accurately mapped the breakpoints of known and previously uncharacterized HBB deletions defining previously uncharacterized deletion breakpoints by PCR amplification and sequencing. The array also successfully identified the common HBA deletions --(SEA) and --(FIL). In summary, comparative genomic hybridization can be used to characterize deletions of the HBA and HBB loci, allowing high-resolution characterization of novel deletions that are not readily detected by PCR-based methods.

A newly modified hemoglobin H inclusion test as a secondary screening for α(0)-thalassemia in Southeast Asian populations

Screening for α(0)-thalassemia is usually associated with a high false-positive rate, leading to an unnecessary PCR workload for accurate diagnosis. We have developed a modified Hb H inclusion test for use as a secondary screening. This test was performed on young red blood cell enriched fractions using dextran sedimentation. The study was performed in 100 subjects positive on initial screening. Confirmatory tests included Hb analysis and a multiplex PCR assay to identify α(0)-thalassemia deletions. A modified Hb H inclusion test was positive in 31 cases, 30 of whom were α(0)-thalassemia carriers (97%). The remaining case (3.0%) was homozygous for α(+)-thalassemia. The remaining 69 cases with a negative Hb H inclusion test included normal subjects, α(+)-thalassemia carriers and β-thalassemia carriers. Two of them (2/69, 3.0%) were found to be double heterozygotes for β(0)-thalassemia and α(0)-thalassemia. The overall sensitivity and specificity of the modified Hb H inclusion test for screening of α(0)-thalassemia were 94.0 and 99.0%, respectively. Therefore, we recommend the use of this test in combination with Hb analysis to exclude cases with αβ-thalassemia. This should lead to a significant reduction in the number of cases referred for PCR analysis of α(0)-thalassemia by about 50.0%.

A multicenter trial of the effectiveness of zeta-globin enzyme-linked immunosorbent assay and hemoglobin H inclusion body screening for the detection of alpha0-thalassemia trait

Routine laboratories use a hemoglobin H (HbH) screen to detect alpha-thalassemia carriers of fatal hemoglobin Bart's hydrops fetalis. This test is laborious and has sensitivity concerns. A commercial zeta-globin enzyme-linked immunosorbent assay (ELISA) is effective in detecting Southeast Asian (SEA) alpha-thalassemia. We present results of a study of the effectiveness of carrier detection of ELISA and a shortened HbH screen compared with gap polymerase chain reaction. ELISA was superior to the HbH screen for the SEA alpha0-thalassemia trait. The ELISA and H screen were equal for detection of all carriers encountered and combined were more effective than either test alone. A positive zeta-globin ELISA result is diagnostic of SEA alpha-thalassemia, and routine use of the zeta-globin ELISA in combination with a shortened HbH screen will improve the efficacy of prenatal screening for carriers of hemoglobin Bart's hydrops fetalis through improved detection and referral for follow-up DNA testing.

Prevalence of erythrocyte haemoglobin H inclusions in unselected patients with clonal myeloid disorders

Patients with clonal myeloid disorders, especially myelodysplastic syndromes (MDS), may acquire alpha-thalassaemia. To estimate the prevalence of this erythrocyte phenotype, we examined brilliant cresyl blue-stained blood smears from 201 patients with neoplastic myeloid disorders and 282 controls (195 non-clonal anaemia, 62 with medical illnesses without anaemia and 25 healthy persons). Haemoglobin H inclusions were detected in 8/100 patients with MDS (8%) and 2/81 (2.5%) patients with myeloproliferative disorders, but in none of the acute leukaemia patients or controls. We conclude that the emergence of thalassaemic clones may be relatively common in the disordered marrow milieu of MDS.

An improved method for the diagnostic approach of alpha+-thalassaemia

An improved method for the diagnostic approach of alpha(+)-thalassaemia is described. The method is based on five common parameters: absence of iron deficiency, mild morphological abnormalities of erythrocytes, normal or slightly reduced erythrocytic indices MCV and MCH, normal chromatographic findings, and presence of haemoglobin H inclusions in erythrocytes with methyl-violet stain after, but not before, incubation with oxidant agent. We studied by DNA analysis, 58 subjects fulfilling the above mentioned diagnostic criteria and we found that 50 of them (86.2%) had a alpha-globin gene defect. In the remaining eight subjects (13.8%) no alpha-gene defect could be documented with the techniques used in the DNA analysis, which detect the six well-known alpha(+)-thalassaemic defects in the Greek population. We conclude that the improved method, we described has a high sensitivity and accuracy in the screening of alpha(+)-thalassaemia.

Hemolysis of erythrocytes by granulysin-derived peptides but not by granulysin

Granulysin, a 9-kDa protein localized in human cytolytic T lymphocytes and natural killer cell granules, is cytolytic against tumors and microbes but not against red blood cells. Synthetic peptides corresponding to the central region of granulysin recapitulate the lytic activity of the intact molecule, and some peptides cause hemolysis of red blood cells. Peptides in which cysteine residues were replaced by serine maintain their activity against microbes but lose activity against human cells, suggesting their potential as antibiotics. Studies were undertaken to determine the mechanism of resistance of red blood cells to granulysin and sensitivity to a subset of granulysin-derived peptides. Granulysin lyses immature reticulocytes, which have mitochondria, but not red blood cells. Granulysin lyses U937 cells but not U937 cells lacking mitochondrial DNA and a functional respiratory chain (U937rho(o) degrees cells), further demonstrating the requirement of intact mitochondria for granulysin-mediated death. Peptide G8, which corresponds to helix 2/loop 2/helix 3, lyses red blood cells, while peptide G9, which is identical except that the cysteine residues were replaced by serine, does not lyse red blood cells. Granulysin peptide-induced hemolysis is markedly inhibited by an anion transporter inhibitor and by Na(+), K(+), and Ca(2+) channel blockers but not by Na(+)/K(+) pump, cotransport, or Cl(-) channel blockers. Although recombinant granulysin and G9 peptide do not induce hemolysis, they both competitively inhibit G8-induced hemolysis. The finding that some derivatives of granulysin are hemolytic may have important implications for the design of granulysin-based antimicrobial therapeutics.

A novel apoptosis pathway activated by the carboxyl terminus of p21

Delivery of biologically active peptides into cells may help elucidate intracellular signal transduction pathways, identify additional in vivo functions, and develop new therapeutics. Although p21 was first identified as a major regulator of cell cycle progression, it is now clear that p21 subserves multiple functions. The amino terminus of p21 interacts with cyclins and cyclin-dependent kinases, while the carboxyl terminus interacts with proliferating cell nuclear antigen (PCNA), growth arrest and DNA damage-inducible gene 45 (GADD45), calmodulin, SET, and CCAAT/enhancer binding protein-alpha (C/EBP-alpha). A chimeric peptide, p21-IRS, consisting of the carboxyl terminal domain of p21 conjugated to a pentapeptide (RYIRS) rapidly enters lymphoid cells and activates apoptosis. In the present study, we investigate the molecular events involved in p21-activated apoptosis. Comparison of p21-IRS with other known proapoptotic agents demonstrates that p21-IRS activates a novel apoptotic pathway: mitochondria are central to the process, but caspases and a decrease in Deltapsi(m) are not involved. Targeting the p21 peptide to specific cell populations may allow development of novel therapies to eliminate aberrant cells in human diseases.