The rare hemoglobin variant Hb Mizuho: report of a Swiss family and literature review

Extreme Reticulocytosis After Splenectomy in a Patient With Hemoglobin Mizuho

BACKGROUND

Patients with Hb Mizuho may be splenectomized at a young age to decrease their need for blood transfusions.

OBSERVATIONS

Transfusion-dependency decreased dramatically in a 4-year-old white boy with Hb Mizuho after splenectomy. Surprisingly, he developed reticulocytosis (>1000×10 9 /L) with a peak reticulocyte percentage of 49%, and erythrocyte abnormalities, including Heinz bodies, Howell-Jolly bodies, and basophilic stippling. Manual reticulocyte counting and flow cytometric measurement with anti-CD71 antibodies supported a truly elevated reticulocyte count.

CONCLUSIONS

We propose possible explanations for the extreme reticulocytosis that arose postsplenectomy and compare the reticulocyte count in the present case with previously published cases.

Hb Mizuho Case Report; Early Genomic Testing Facilitates a Life Changing Diagnosis

Unstable variant hemoglobinopathies are an uncommon cause of hemolysis in the pediatric patient and may cause a delay in diagnosis if there is not a high index of suspicion. Hemoglobin (Hb) Mizuho is a rare unstable hemoglobinopathy caused by a pathogenic variant of the HBB gene with a severe phenotype. Here we report on the first known case of Hb Mizuho in Australia, presenting with features of acute and chronic hemolysis. The morphological features on blood film review, in conjunction with biochemical findings and other clinical features, did not immediately suggest an alternative diagnosis and a Next Generation Sequencing gene analysis approach was taken to investigate genes associated with red blood cell disorders and atypical uremic syndrome. The HBB Mizuho variant was detected and established the diagnosis. This report highlights the challenge of diagnosing Hb Mizuho on conventional testing and the need for early genomic testing to clarify a diagnosis.

Hb Mizuho (HBB: c.206T>C): Pitfalls of Screening Tests in an Unstable Hemoglobin Variant Diagnosed after Targeted Next-Generation Sequencing

Hyperunstable hemoglobins (Hbs) are challenging to diagnose and may be missed on conventional hemolytic anemia work-up. Here, we report the case of a 2-year-old Indian boy with infancy-onset severe hemolytic anemia. Its etiology was revealed by targeted next-generation sequencing (NGS) to be the rare Hb Mizuho (HBB: c.206T>C). This variant had been missed on the initial routine laboratory investigations (heat and isopropanol tests for unstable Hbs) owing to its hyperunstable nature.