Screening for clinically significant non-deletional alpha thalassaemia mutations by pyrosequencing

Multi-allele DNA biosensor for the rapid genotyping of 'nondeletion' alpha thalassaemia mutations in HBA1 and HBA2 genes by means of multiplex primer extension reaction

BACKGROUND

Alpha-thalassaemia is an autosomal recessive disorder characterized by defective production of the alpha chain of haemoglobin. It is caused mainly by deletions of one or both of the duplicated alpha-globin genes on chromosome 16, and/or by nucleotide variations, known as "nondeletion" mutations. Definition of the alpha globin genotype in carriers supports genetic counselling, and in patients with Hb H disease is useful to predict prognosis and management options. Here, we report a method that facilitates direct detection by naked eye of the 13 most common "nondeletion" alpha-globin gene mutations in populations around the Mediterranean and Middle East.

METHODS AND RESULTS

The method comprises (i) PCR amplification of a single 1087 bp fragment for each HBA1 and HBA2 gene (separately); (ii) multiplex primer extension reaction of just 10 cycles, using unpurified amplification product as a template, to incorporate biotin into those allele-specific primers that extend and, finally, (iii) visual detection of the reaction products within minutes by the dipstick biosensor. The method was evaluated by analysing 105 samples of known genotypes and the results were found fully concordant with those obtained by the reference methods.

CONCLUSIONS

The proposed assay is particularly suited for small molecular-diagnostic laboratories with a limited budget and a low-to-medium sample volume. In addition this platform represents a very simple and useful genotyping tool to support gene scanning methods whenever nucleotide variations have to be specified.

EMQN Best Practice Guidelines for molecular and haematology methods for carrier identification and prenatal diagnosis of the haemoglobinopathies

Haemoglobinopathies constitute the commonest recessive monogenic disorders worldwide, and the treatment of affected individuals presents a substantial global disease burden. Carrier identification and prenatal diagnosis represent valuable procedures that identify couples at risk for having affected children, so that they can be offered options to have healthy offspring. Molecular diagnosis facilitates prenatal diagnosis and definitive diagnosis of carriers and patients (especially ‘atypical' cases who often have complex genotype interactions). However, the haemoglobin disorders are unique among all genetic diseases in that identification of carriers is preferable by haematological (biochemical) tests rather than DNA analysis. These Best Practice guidelines offer an overview of recommended strategies and methods for carrier identification and prenatal diagnosis of haemoglobinopathies, and emphasize the importance of appropriately applying and interpreting haematological tests in supporting the optimum application and evaluation of globin gene DNA analysis.

Advances in technologies for screening and diagnosis of hemoglobinopathies

Hemoglobinopathies constitute the most common monogenic disorders worldwide, caused by mutations in the globin genes that synthesize the globin chains of hemoglobin. Synthesis may be reduced (thalassemia) or underlie abnormal hemoglobins. Mutation interactions produce a wide range of disorders. For neonatal and antenatal screening, identification of affected newborns or carriers is achieved by hematological tests. DNA analysis supports definitive diagnosis, and additionally facilitates prenatal diagnosis procedures. Most methods used today have been developed over several decades, with few recent advances in hematology methods. However, DNA methods evolve continuously. With global migration and multiethnic societies the trend is from targeted, population-specific methods towards generic methods, such as Sanger sequencing (point mutations) and multiplex ligation probe amplification (deletions). DNA microarrays constitute an advanced DNA method for some mutation categories. The newest DNA technology is next-generation sequencing. Although not completely ready for routine use currently, next-generation sequencing may soon become a reality for some hemoglobin diagnostic laboratories.

A combination of two novel alpha globin variants Hb Bridlington (HBA1) and Hb Taybe (HBA2) resulting in severe hemolysis, pulmonary hypertension, and death

OBJECTIVE AND IMPORTANCE

To describe two novel hemoglobin mutations that resulted in an unstable hemoglobin with a severe hemolytic phenotype.

CLINICAL PRESENTATION

A patient with an unstable hemoglobin and chronic hemolysis underwent splenectomy at age 15, subsequently developing chronic thrombo-embolic pulmonary hypertension at age 27 that was ultimately fatal.

INTERVENTION

DNA sequencing of the alpha globin gene revealed heterozygous inheritance of Hb Taybe, arising from a novel mutation in the HBA2 gene and Hb Bridlington, a novel HBA1 mutation. Greater disease severity is predicted by the position of the Hb Taybe mutation on the HBA2 gene (which transcribes more globin than the HBA1 gene).

CONCLUSION

Splenectomy was not clearly beneficial and may have contributed to the development of pulmonary hypertension. The case favors a cautious approach when considering splenectomy for patients with Hb Taybe.

Impact of isolated germline JAK2V617I mutation on human hematopoiesis

The association between somatic JAK2 mutation and myeloproliferative neoplasms (MPNs) is now well established. However, because JAK2 mutations are associated with heterogeneous clinical phenotypes and often occur as secondary genetic events, some aspects of JAK2 mutation biology remain to be understood. We recently described a germline JAK2V617I mutation in a family with hereditary thrombocytosis and herein characterize the hematopoietic and signaling impact of JAK2V617I. Through targeted sequencing of MPN-associated mutations, exome sequencing, and clonality analysis, we demonstrate that JAK2V617I is likely to be the sole driver mutation in JAK2V617I-positive individuals with thrombocytosis. Phenotypic hematopoietic stem cells (HSCs) were increased in the blood and bone marrow of JAK2V617I-positive individuals and were sustained at higher levels than controls after xenotransplantation. In signaling and transcriptional assays, JAK2V617I demonstrated more activity than wild-type JAK2 but substantially less than JAK2V617F. After cytokine stimulation, JAK2V617I resulted in markedly increased downstream signaling compared with wild-type JAK2 and comparable with JAK2V617F. These findings demonstrate that JAK2V617I induces sufficient cytokine hyperresponsiveness in the absence of other molecular events to induce a homogeneous MPN-like phenotype. We also provide evidence that the JAK2V617I mutation may expand the HSC pool, providing insights into both JAK2 mutation biology and MPN disease pathogenesis.

Prenatal, noninvasive and preimplantation genetic diagnosis of inherited disorders: hemoglobinopathies

Disorders of hemoglobin synthesis have been used as a prototype for the development of most approaches for prenatal diagnosis (PND). PND for hemoglobinopathies based on molecular analysis of trophoblast or amniocyte DNA has accumulated approximately 30 years of experience. Disadvantages with conventional PND include 'invasive' fetal sampling and the need to terminate affected ongoing pregnancies. New developments are directed towards improving both the timing and/or safety of procedures. Preimplantation genetic diagnosis, an established procedure with 20 years of clinical application, avoids the need to terminate affected pregnancies through the identification and selective transfer of unaffected in vitro fertilization embryos. Approaches towards 'noninvasive' PND, through analyzing fetal cells or free fetal DNA present in the circulation of pregnant women, are a focus of ongoing research. Overall, PND, preimplantation genetic diagnosis (and potentially 'noninvasive' PND) represent valuable reproductive options for couples at risk of having a child affected with a severe inherited disease.