Clinical Genotyping by Next Generation Sequencing Reveals a Novel, De Novo β-Globin Gene Mutation Causing Hemolytic Anemia in a Chinese Individual

A Novel Frameshift Mutation of HBB Causing Dominant β-Thalassemia in a Chinese Individual

We reported a rare β-thalassemia patient, a 41-year-old Chinese male with small cell hypopigmentation anemia, jaundice and splenomegaly as the main clinical symptoms. By using Next-Generation Sequencing (NGS), we identified a novel de novo HBB mutation(c.358_365dup, p.Phe123Alafs*39) which resulted in an abnormally prolonged β-globin chain comprising 159 amino acid residues. The secondary and three-dimensional structures of the β-globin predicted that the novel prolonged β-globin chain has a considerable risk of instability in the hemoglobin, and leads to clinical phenotype. This study contributes to the enrichment of the genetic pathogenic mutation database for thalassemia and underscores the significance of NGS in the screening of mutations for thalassemia families.

Dominant β-Thalassemia Phenotype Caused by Hb Dieppe (HBB: c.383A>G): Another Case Report

Homozygous or compound heterozygous mutations of the β-globin gene lead to β-thalassemia (β-thal) major (β-TM) or β-thal intermedia (β-TI), whereas heterozygotes usually show microcytosis with negligible or no hemolysis. Certain missense mutations in exon 3, however, produce unstable globins causing a dominant β-thal phenotype or hemolytic anemia in heterozygotes. Here we report a mutation in exon 3 of the β-globin gene, which results in an unstable globin (Hb Dieppe) [β127(H5)Gln→Arg; HBB: c.383A>G] with a dominant β-thal phenotype in two generations of a Chinese family. Physicians should be alerted to this mechanism of β-thal considering its relative rarity.

Hemoglobin Yamagata [β132(H10)Lys→Asn; (HBB: c.399A>T)]: a mosaic to be put together

OBJECTIVES

Artifactually altered glycated hemoglobin (HbA_1c) concentrations are frequently linked to hemoglobin (Hb) variants. Their expression and detection require in-depth analysis.

METHODS

Cation exchange high performance liquid chromatography (HPLC) (Bio-Rad Variant™ II; Trinity Biotech Premier Hb9210 Resolution), capillary electrophoresis (CE) (Sebia Capillarys 2 Flex Piercing) and mass spectrometry (MS) (Waters) were used for variant detection; Sanger sequencing, multiplex ligation-dependent probe amplification (MLPA) and next generation sequencing (NGS) were used for DNA analysis; HbA_1c was measured with cation exchange HPLC (Bio-Rad Variant™ II; Arkray Adams HA-8180V; Tosoh HLC-723 G7), CE (Sebia Capillarys 2 Flex Piercing), boronate affinity HPLC (Trinity Biotech Hb9210 Premier), immunoassay (Cobas c501 Tina-quant HbA_1c Gen. 3; Nihon Kohden CHM-4100 Celltac chemi HbA_1c HA-411V) and enzymatic assay (Abbott Architect c 8000 HbA_1c).

RESULTS

Hb Yamagata [β132(H10)Lys→Asn; (HBB: c.399A>T)] was identified in the proband by MS after the observation of an abnormal peak in HPLC and CE. A mosaic expression of this variant was detected by NGS (mutant: 8%; wild type: 92%), after negative results in Sanger sequencing. Hb Yamagata interfered with HbA_1c measurements by cation exchange HPLC and CE whereas immuno and enzymatic assay values showed good agreement with boronate affinity HPLC measurement.

CONCLUSIONS

A mosaicism of Hb Yamagata was found in a patient with altered HbA_1c values. This rare gene variant was detected only by advanced technologies as MS and NGS. The variant interfered with common HbA_1c determination methods.

A De Novo Heterozygous Variant (HBB: c.379delG, p.Val127Cysfs*32) Associated with a Mild β-Thalassemia Intermedia Phenotype in a Turkish Child

We report a de novo heterozygous variant of the β-globin chain that showing a mild β-thalassemia intermedia (β-TI) phenotype. He presented with mild anemia, splenomegaly, reticulocytosis, and poikilocytosis and tear drop cells on the blood smear; Immune mediated hemolysis, red cell membrane and enzyme defects, were excluded; hemoglobin (Hb) electrophoresis showed an elevation of Hb F. Molecular analysis of the β-globin gene showed a heterozygous variation in exon 3 (HBB: c.379delG, p.Val127Cysfs*32) in the absence of an α-globin gene mutation or mutations that modulate Hb F expression.