Homozygosity mapping reveals founder SEC23B-Y462C mutations in Indian congenital dyserythropoietic anemia type II

Development of High-Resolution Melting Curve Analysis for rapid detection of SEC23B gene mutation causing Congenital Dyserythropoietic Anemia type II in Indian population

BACKGROUND

Congenital dyserythropoietic anemias (CDAs) are a very rare and heterogeneous group of disorders characterized by ineffective erythropoiesis. CDA II is caused by mutations in the SEC23B gene. The most common mutation reported in India is c.1385 A > G, p.Y462C. There is no simple and cost-effective confirmatory diagnostic test available for CDA, and therefore, many patients remain undiagnosed. High-resolution melting curve (HRM) analysis is a polymerase chain reaction (PCR) based technique applied to identify genetic differences and scan nucleic acid sequences. HRM can be used to rapidly screen the common mutation causing CDA II in the Indian population. Thus, we studied the use of High-Resolution Melting Curve Analysis to detect common mutation causing CDA II in the Indian population.

METHOD

11 patients having SEC23B (Y462C) mutation causing CDA II are considered for this study. HRM was used to check the presence of Y462C mutation. To verify the accuracy of the HRM analysis, we compared HRM results with the results of Sanger sequencing. This helped us to confirm the diagnosis.

RESULTS

We have described the clinical, hematological, and genetic data of eleven patients suffering from CDAII. According to HRM and Sanger sequencing, a homozygous SEC23B (Y462C) mutation was present in all patients, whereas a heterozygous Y462C mutation was present in their parents.

CONCLUSION

Our data showed that High-Resolution Melting (HRM) analysis could be used to rapidly screen common SEC23B mutation that causes CDA II in the Indian population.

Congenital dyserythropoietic anemias

Congenital dyserythropoietic anemias (CDAs) are a heterogeneous group of inherited anemias that affect the normal differentiation-proliferation pathways of the erythroid lineage. They belong to the wide group of ineffective erythropoiesis conditions that mainly result in monolinear cytopenia. CDAs are classified into the 3 major types (I, II, III), plus the transcription factor-related CDAs, and the CDA variants, on the basis of the distinctive morphological, clinical, and genetic features. Next-generation sequencing has revolutionized the field of diagnosis of and research into CDAs, with reduced time to diagnosis, and ameliorated differential diagnosis in terms of identification of new causative/modifier genes and polygenic conditions. The main improvements regarding CDAs have been in the study of iron metabolism in CDAII. The erythroblast-derived hormone erythroferrone specifically inhibits hepcidin production, and its role in the mediation of hepatic iron overload has been dissected out. We discuss here the most recent advances in this field regarding the molecular genetics and pathogenic mechanisms of CDAs, through an analysis of the clinical and molecular classifications, and the complications and clinical management of patients. We summarize also the main cellular and animal models developed to date and the possible future therapies.

Compound heterozygous variants in NBAS as a cause of atypical osteogenesis imperfecta

BACKGROUND

Osteogenesis imperfecta (OI), the commonest inherited bone fragility disorder, affects 1 in 15,000 live births resulting in frequent fractures and reduced mobility, with significant impact on quality of life. Early diagnosis is important, as therapeutic advances can lead to improved clinical outcome and patient benefit.

REPORT

Whole exome sequencing in patients with OI identified, in two patients with a multi-system phenotype, compound heterozygous variants in NBAS (neuroblastoma amplified sequence). Patient 1: NBAS c.5741G>A p.(Arg1914His); c.3010C>T p.(Arg1004*) in a 10-year old boy with significant short stature, bone fragility requiring treatment with bisphosphonates, developmental delay and immunodeficiency. Patient 2: NBAS c.5741G>A p.(Arg1914His); c.2032C>T p.(Gln678*) in a 5-year old boy with similar presenting features, bone fragility, mild developmental delay, abnormal liver function tests and immunodeficiency.

DISCUSSION

Homozygous missense NBAS variants cause SOPH syndrome (short stature; optic atrophy; Pelger-Huet anomaly), the same missense variant was found in our patients on one allele and a nonsense variant in the other allele. Recent literature suggests a multi-system phenotype. In this study, patient fibroblasts have shown reduced collagen expression, compared to control cells and RNAseq studies, in bone cells show that NBAS is expressed in osteoblasts and osteocytes of rodents and primates. These findings provide proof-of-concept that NBAS mutations have mechanistic effects in bone, and that NBAS variants are a novel cause of bone fragility, which is distinguishable from 'Classical' OI.

CONCLUSIONS

Here we report on variants in NBAS, as a cause of bone fragility in humans, and expand the phenotypic spectrum associated with NBAS. We explore the mechanism underlying NBAS and the striking skeletal phenotype in our patients.

Diagnosis and management of congenital dyserythropoietic anemias

Congenital dyserythropoietic anemias (CDAs) are inherited disorders hallmarked by chronic hyporegenerative anemia, relative reticulocytopenia, hemolytic component and iron overload. They represent a subtype of the inherited bone marrow failure syndromes, characterized by impaired differentiation and proliferation of the erythroid lineage. Three classical types were defined by marrow morphology, even if the most recent classification recognized six different genetic types. The pathomechanisms of CDAs are different, but all seem to involve the regulation of DNA replication and cell division. CDAs are often misdiagnosed, since either morphological abnormalities or clinical features can be commonly identified in other clinically-related anemias. However, differential diagnosis is essential for guiding both follow up and management of the patients.