Newborn screening for hemoglobinopathies in California

Newborn screening for hemoglobinopathies using capillary electrophoresis technology: Testing the Capillarys Neonat Fast Hb device

OBJECTIVES

To diagnose hemoglobinopathies in newborns by separating and measuring the Hb fractions on high throughput capillary electrophoresis. To test and validate the Capillarys Neonat Fast Hb device (Sebia) on fresh and dry blood samples.

DESIGN AND METHODS

The Hb fractions in 1.600 cord blood samples from the multi ethnic Dutch population were separated and measured. Further, the sensitivity, specificity and reproducibility of the device in detecting abnormalities and measuring the Hb fractions were estimated.

RESULTS

The apparatus separated all significant Hb fractions that should be detected during newborn screening (NBS) with 100% sensitivity. The reproducibility of the migrations guaranteed putative specificity for the few relevant frequent variants observed (HbS, C, and E). The estimation of the HbA and F fractions proved reliable using a well-designed integration mode.

DISCUSSION

Due to the limited number of samples no cases with sickle cell disease or β-thalassemia major were found in this cohort. However, the heterozygous state for the common variants associated with these diseases was clearly recognizable. The measurements were sufficiently precise to recognize sickle cell disease, β-thalassemia major and intermedia and to identify carriers including possible β-thalassemia. Therefore, Capillarys Neonat Fast Hb (Sebia) can be considered as a valid instrument for NBS of the Hemoglobinopathies on fresh and dry blood samples.

Comprehensive and efficient HBB mutation analysis for detection of beta-hemoglobinopathies in a pan-ethnic population

Current methods that assay hemoglobin beta-globin chain variants can have limited clinical sensitivity when applied techniques identify only a predefined panel of mutations. Even sequence-based assays may be limited depending on which gene regions are investigated. We sought to develop a clinically practical yet inclusive molecular assay to identify beta-globin mutations in multicultural populations. We highlight the beta-globin mutation detection assay (beta-GMDA), an extensive gene sequencing assay. The polymerase chain reaction (PCR) primers are located to encompass virtually all hemoglobin beta locus (HBB) mutations. In addition, this assay is able to detect, by gap PCR, a common large deletion (Delta619 base pair), which would be missed by sequencing alone. We describe our 5-year experience with the beta-GMDA and indicate its capability for detecting homozygous, heterozygous, and compound heterozygous sequence changes, including previously unknown HBB variants. The beta-GMDA offers superior sensitivity and ease of use with comprehensive detection of HBB mutations that result in beta-globin chain variants.

Newborn screening

Early detection of many disorders, mainly inherited, is feasible with population-wide analysis of newborn dried blood spot samples. Phenylketonuria was the prototype disorder for newborn screening (NBS) and early dietary treatment has resulted in vastly improved outcomes for this disorder. Testing for primary hypothyroidism and cystic fibrosis (CF) was later added to NBS programs following the development of robust immunoassays and molecular testing. Current CF testing usually relies on a combined immunoreactive trypsin/mutation detection strategy. Multiplex testing for approximately 25 inborn errors of metabolism using tandem mass spectrometry is a relatively recent addition to NBS. The simultaneous introduction of many disorders has caused some re-evaluation of the traditional guidelines for NBS, because very rare disorders or disorders without good treatments can be included with minimal effort. NBS tests for many other disorders have been developed, but these are less uniformly applied or are currently considered developmental. This review focuses on Australasian NBS practices.

Population estimates of sickle cell disease in the U.S

BACKGROUND

The number of individuals with sickle cell disease (SCD) in the U.S. is unknown. Determination of burden of disease, healthcare issues, and policies is best served by representative estimations of the SCD population.

PURPOSE

To update SCD population estimates by using recent U.S. Census and birth-cohort SCD prevalence for at-risk populations as available through the centralized reporting of universal newborn screening for hemoglobinopathies, with an effort to demonstrate the potential effect of early mortality.

METHODS

National and state SCD populations were estimated based on the 2008 U.S. Census, using total, African-American, and Hispanic birth-cohort disease prevalence derived from the National Newborn Screening Information System. Estimates were corrected for early mortality for sickle cell anemia using data from the CDC's Compressed Mortality Report and published patient-cohort survival information.

RESULTS

National SCD population estimates ranged from 104,000 to 138,900, based on birth-cohort disease prevalence, but from 72,000 to 98,000 when corrected for early mortality. Several limitations were noted in the available data, particularly for SCD mortality in adults.

CONCLUSIONS

The number of individuals with SCD in the U.S. may approach 100,000, even when accounting for the effect of early mortality on estimations. A paucity of high-quality data limits appropriate estimation. State-to-state variability may preclude application of state-specific information to other states or to the nation as a whole. Standardized collection and centralized reporting, a surveillance system, will be necessary to assess the size and composition of the U.S. SCD population.

History and current status of newborn screening for hemoglobinopathies

The impact of hemoglobinopathies on healthcare in the United States, particularly sickle cell disease (SCD), has been significant. Enactment of the Sickle Cell Anemia Control Act in 1972 significantly increased the federal interest in the SCDs and other hemoglobinopathies. Only since May 1, 2006, have all states required and provided universal newborn screening for SCD despite a national recommendation to this effect in 1987. In this article, we review the history of screening for SCD and other hemoglobinopathies, along with federal and state activities that have contributed to improved health outcomes for patients with SCD, as well as current newborn screening practices. We also chronicle the federal activities that have helped to shape and to refine laboratory screening and diagnostic proficiency. Finally, we review molecular testing strategies that have evolved and outline their possible future impacts on disease detection and outcome improvement.

Evaluation of the validity and utility of genetic testing for rare diseases

The conventional criteria for evaluating genetic tests include analytic validity, clinical validity, and clinical utility. Analytical validity refers to a test's ability to measure the genotype of interest accurately and reliably. Clinical validity refers to a test's ability to detect or predict the clinical disorder or phenotype associated with the genotype. Clinical utility of a test is a measure of its usefulness in the clinic and resulting changes in clinical endpoints. In addition, the utility to individuals and families of genomic information, or personal utility, should be considered. This chapter identifies methodological and data issues involved in assessing each type of validity or utility. The validity and utility of a test must be considered in a specific context, which include diagnostic testing, newborn screening, prenatal carrier screening, and family or cascade screening. Specific rare disorders addressed include cystic fibrosis, fragile X syndrome, Duchenne and Becker muscular dystrophy, spinal muscular atrophy, Huntington disease, as well as cancer associated with BRCA mutations.

The epidemiology of abnormal hemoglobins in Mediterranean high-level athletes

The aim of this study was to determine the prevalence and nature of hemoglobin (Hb) defects in a Mediterranean high-level (HL) athlete population. Five hundred and ninety-four HL male and female athletes were recruited during the annual follow-up of the members of Tunisian national teams. Hematological data, Hb electrophoresis, and DNA analysis were assessed using conventional techniques. Sporting discipline, type of sport, and performance levels were assessed using a questionnaire. The results showed that 32 HL athletes had abnormal Hb (5.4%): beta-thalassemia (2.2%), alpha-thalassemia (0.5%), HbAS (1.5%), HbAC (0.5%), and rare Hb variants (0.7%). Of the 32 defect carriers, all but one (a alpha-thalassemia) were heterozygous. All the detected hemoglobinopathies but one (an Hb Hope) had already been reported in the country. The prevalence of Hb defect in the HL athletes was similar to that described in the general Tunisian population (P > 0.05). The percentage of Hb defect in the athletes was not dependent on gender, or performance level (P > 0.05). Within each type of sport the percentages of athletes with normal and abnormal Hb were similar (P > 0.05). The hematological data revealed the diversity of anemia, microcytosis, and hypochromia in thalassemic HL athletes. We concluded that HL athletes in Tunisia were a representative sample of the general Tunisian population regarding the prevalence and nature of benign abnormal Hb. The hematological data of the thalassemia carriers exhibited high variability and raised the question of genetic and sporting counseling, as well as biological follow-up for these carriers.

Hemoglobin H-constant spring in North America: an alpha thalassemia with frequent complications

Hemoglobin H-constant spring (Hb H-CS), the most common nondeletional alpha thalassemia in Asia is increasingly recognized in North America due to shifts in immigration patterns. In California, alpha (α)-thalassemia syndromes are the second most frequent finding among newborns screened for hemoglobinopathies with a two-fold increase compared to a decade earlier [1 ,2 ]. Though known to have a more severe anemia than Hb H disease, the other clinical findings of Hb H-CS are not well described. Moreover, beneficial therapies that have become available in the last decade are often not applied to their care. This analysis of 46 patients enrolled in the Thalassemia Clinical Research Network (TCRN) age 13+/− 10 years old, with Hb H-CS revealed moderate anemia (mean 8.7 ± 1.5 g/dl), regular transfusion therapy in 24% of patients, and splenomegaly or prior splenectomy in one-third of them. Serum transferin receptor (sTfr), was elevated; (44.4 ± 18 mcg/ml normal range 2.9–8.3 mcg/ml), reflecting ineffective erythropoiesis, which in turn leads to high iron absorption and increased ferritin levels in younger (median = 187 ng/ml) and older (median = 465 ng/ml) nontransfused patients. These findings along with moderate growth delay and low bone mass were more prevalent in Hb H-CS patients compared to deletional Hb H disease. Our results highlight the required monitoring of the extent of anemia, growth, splenomegaly, iron overload, gallstones, bone density and assessment of need for transfusions and specific treatments for disease complications.

The significance of the hemoglobin A(2) value in screening for hemoglobinopathies

BACKGROUND AND OBJECTIVE

The inherited hemoglobinopathies are a large group of disorders that include thalassemias and hemoglobin variants. Accurate determination of the carrier phenotype is essential for detecting couples at risk for producing offspring with hemoglobinopathy. Heterozygous beta-thalassemia is usually silent at the clinical level. His phenotype is characterized by microcytosis and hypochromia with increased hemoglobin A(2) (HbA(2)) value. Therefore, HbA(2) determination plays a key role in screening programs for hemoglobinopathy. The aim of this review is to address and suggest an approach for reducing or abolishing hemoglobinopathy screening mistakes.

DESIGN AND METHODS

Quantitative methods for HbA(2) value determination, comment on the accuracy of the test and on the interpretation of data were discussed. The most probable diagnostic conclusion based on the HbA(2) level, hemoglobin pattern, hematological parameters and iron markers was suggested in this review.

RESULTS

Hemoglobinopathies are the only genetic disease where it is possible to detect carriers using hematological findings rather than DNA analysis. However, hematological diagnosis is sometimes presumptive, and in these cases, DNA analysis becomes necessary. Complete screening is based on the detection of red cell indices, HbA(2), HbF and hemoglobin variant values. In particular, HbA(2) determination plays a key role in screening programs for beta-thalassemia because a small increase in this fraction is one of the most important markers of beta-thalassemia heterozygous carriers.

CONCLUSION

Genetic factors both related and unrelated to the beta- and alpha-globin gene clusters, iron metabolism, endocrinological disorders, and some types of anemia, together with intra- and inter-laboratory variations in HbA(2) determination, may cause difficulties in evaluating this measurement in screening programs for hemoglobinopathies. Therefore, knowledge of all these issues is important for reducing or eliminating the risk of mistakes in screening programs for hemoglobinopathies.

Alpha thalassemia major--new mutations, intrauterine management, and outcomes

Alpha thalassemia disorders are a group of hereditary anemias caused by absent or decreased production of the alpha chain of hemoglobin. Hemoglobin Bart's hydrops fetalis is usually a fatal in-utero disease caused by absence of the alpha genes. However, the molecular and genotypic expression of hemoglobin Bart's varies and increasing numbers of births are being reported. Population screening and prenatal diagnosis of at-risk couples is essential but often not performed. Most affected pregnancies are often undetected, resulting in severe fetal and maternal complications. Noninvasive monitoring by Doppler ultrasonagraphy with intrauterine transfusion therapy has changed the prognosis for this disorder. These advances in intrauterine and postnatal therapy have resulted in ethical dilemmas for the family and the provider.

Newborn screening for non-sickling hemoglobinopathies

The hemoglobinopathies encompass a heterogeneous group of disorders associated with mutations in both the alpha-globin and beta-globin genes. Non-sickling disorders are found primarily in individuals of Mediterranean, Asian and Southeast Asian ancestry. With rapid growth in the Asian and Hispanic segments of the US population, the geographic distribution of hemoglobinopathies is expected to become significantly different from what it is today. The epidemiologic changes in the prevalence of non-sickling hemoglobin disorders have important implications for future public health programs, including newborn screening.

The purpose of newborn screening for hemoglobinopathies is to identify clinically significant disorders and provide early education and specialized care prior to the onset of clinical symptoms. Although newborn screening for sickle cell disease is mandated in all states, screening for non-sickling hemoglobinopathies is directed in only one state and limited to reporting of a presumptive diagnosis in most other states. Early delivery of comprehensive care, as well as new and potentially curative therapies, has significantly improved the prognosis for affected patients. This review will consider the increasing prevalence of once uncommon hemoglobinopathies in the US, highlighting the rationale for expanding newborn screening beyond sickle cell disorders.