Algorithmic evaluation of hereditary erythrocytosis: Pathways and caveats

A Screening Approach for Inherited Erythrocytosis due to the VHL:c.598C > T Mutation (Chuvash Polycythemia)

Genetic work-up of unexplained erythrocytosis that is suspected to be inherited in nature currently requires either laborious exon-by-exon gene panel testing by Sanger sequencing or expensive next-generation sequencing. A high prevalence of Chuvash polycythemia (61%) has been previously reported among north Indian erythrocytosis patients. We assessed PCR-RFLP for VHL c.598C > T mutation as a first-line test in 99 persons with JAK2 V617F-negative, unexplained erythrocytosis. We enrolled two groups: Group A (n = 38) had erythrocytosis patients (n = 33) or their first-degree relatives (n = 5), and, Group B with 61 healthy blood donation volunteers who were deferred after the discovery of unexplained high hemoglobin levels. Detailed history and clinical examination, hemogram, erythropoietin levels and PCR-RFLP for the VHL:c.598C > T;p.R200W mutation were done. In Group A, three (8%) persons aged 9, 13 and 30-years were homozygous for VHL:c.598C > T. Two were heterozygous (parents of a known case of Chuvash polycythemia). None of the Group B subjects had the Chuvash mutation. Erythropoietin levels in group A were low in 5/26 cases (19%) and normal in 18/26 (69%). In Group B, seven (11%) donors had normal values while the remaining 54 (89%) had high erythropoietin levels. Despite a lower frequency (8%) compared to literature, our results suggest that the relatively simpler PCR-RFLP for VHL:c.598C > T mutation may be considered for the initial genetic screening of unexplained, suspected congenital erythrocytosis in regions where Chuvash polycythemia comprises a large proportion of inherited erythrocytosis, after polycythemia vera and common acquired secondary causes are excluded.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12288-023-01668-9.

Diagnosis and genetic analysis of polycythemia in children and a novel EPAS1 gene mutation

BACKGROUND

Unlike in adults, there is no consensus on management and diagnosis of polycythemia in children. This study aims to evaluate the diagnosis and verify the algorithm in children with polycythemia.

METHODS

Seventy-nine children with polycythemia were followed-up in our pediatric hematology-oncology clinic between December 15, 2019, and July 15, 2021. After eliminating secondary causes (hypoxia, pulmonary, cardiac diseases), we checked for genetic mutations, including congenital erythrocytosis gene panel (JAK, EPOR, EPAS1, EGNL1, HBB, HBA, BPGM, and VHL). We also compared parameters for secondary and idiopathic polycythemia groups.

RESULTS

Of the 79 children, thirty-five had secondary polycythemia (hypoxia, pulmonary, cardiac diseases), and one was diagnosed with a novel likely pathogenic mutation c.2089C  >  G; p.Pro697Ala in exon 13 of EPAS1 gene. Others (n = 35) had persistent and idiopathic polycythemia. Here, we compared the idiopathic and secondary cases. We found that the ratio of family history of polycythemia (n = 4 (9.5%) vs 0%, respectively) was higher in the second group (p = 0.009). In addition, the mean age (14.7 ± 3.52 vs 13.4 ± 4.67 respectively) (p = 0.042) and the ratio of erythroid hyperplasia in bone marrow [n = 3 (8.6%) vs 0% respectively] (p = 0.003) was higher in the idiopathic polycythemia group, compared to secondary polycythemia patients.

CONCLUSION

Finding the genetic defect in polycythemia is a significant issue. Due to being a rarity in children, the first line JAK mutation analysis should be performed in selected cases. This study is the first description of a Turkish patient with EPAS1 p.Pro697Ala mutation, thereby expanding our knowledge about the clinical features of the disease. However, new investigations are required to confirm its function.

Unexplained Hematocrit Increase after Therapeutic Phlebotomy in a Patient with Marked Erythrocytosis

We report a patient with hereditary erythrocytosis who underwent a therapeutic phlebotomy and had a post-phlebotomy hematocrit that was higher than the pre-phlebotomy hematocrit. We could not discern a reason for this hematocrit increase after phlebotomy. Instead of performing another phlebotomy, we performed an automated red cell depletion via an apheresis instrument. This procedure is essentially a red cell exchange, but 5% albumin is used as the replacement fluid instead of red blood cells. The patient’s hematocrit decreased from 80% to 39% after three consecutive daily red cell depletion procedures. We share our experience to report the unusual finding of a patient’s hematocrit that increased with phlebotomy and to raise awareness of the red cell depletion procedure.

NGS Evaluation of a Bernese Cohort of Unexplained Erythrocytosis Patients

(1) Background: Clinical and molecular data on patients with unexplained erythrocyto-sis is sparse. We aimed to analyze the clinical and molecular features of patients with congenital erythrocytosis in our tertiary reference center. (2) Methods: In 34 patients with unexplained erythrocytosis, a 13-gene Next-Generation Sequencing erythrocytosis panel developed at our center was conducted. (3) Results: In 6/34 (18%) patients, eight different heterozygous gene variants were found. These patients were, therefore, diagnosed with congenital erythrocytosis. Two patients had two different gene variants each. All variants were characterized as variants of unknown significance as they had not previously been described in the literature. The rest of the patients (28/34, 82%) had no detected gene variants. (4) Conclusions: Our experience shows that the NGS panel can be helpful in determining the reasons for persistent, unexplained erythrocytosis. In our cohort of patients with erythrocytosis, we identified some, thus far unknown, gene variants which may explain the clinical picture. However, further investigations are needed to determine the relationship between the molecular findings and the phenotype.

Diagnosis and management of non-clonal erythrocytosis remains challenging: a single centre clinical experience

Erythrocytosis has a diverse background. While polycythaemia vera has well defined criteria, the diagnostic approach and management of other types of erythrocytosis are more challenging. The aim of study was to retrospectively analyse the aetiology and management of non-clonal erythrocytosis patients referred to a haematology outpatient clinic in an 8-year period using a 3-step algorithm. The first step was inclusion of patients with Hb > 185 g/L and/or Hct > 0.52 in men and Hb > 165 g/L and/or Hct > 0.48 in women on two visits ≥ two months apart, thus confirming true erythrocytosis. Secondly, polycythaemia vera was excluded and secondary causes of erythrocytosis (SE) identified. Thirdly, idiopathic erythrocytosis patients (IE) were referred to next-generation sequencing for possible genetic background evaluation. Of the 116 patients, 75 (65%) are men and 41 (35%) women, with non-clonal erythrocytosis 34/116 (29%) had SE, 15/116 (13%) IE and 67/116 (58%) stayed incompletely characterized (ICE). Patients with SE were significantly older and had significantly higher Hb and Hct compared to patients with IE. Most frequently, SE was attributed to obstructive sleep apnoea and smoking. Phlebotomies were performed in 56, 53 and 40% of patients in the SE, IE, and ICE group, respectively. Approx. 70% of patients in each group received aspirin. Thrombotic events were registered in 12, 20 and 15% of SE, IE and ICE patients, respectively. Congenital erythrocytosis type 4 (ECYT4) was diagnosed in one patient. The study demonstrates real-life management of non-clonal erythrocytosis which could be optimized using a 3-step diagnostic algorithm.

Update on mutations in the HIF: EPO pathway and their role in erythrocytosis

Identification of the underlying defects in congenital erythrocytosis has provided mechanistic insights into the regulation of erythropoiesis and oxygen homeostasis. The Hypoxia Inducible Factor (HIF) pathway plays a key role in this regard. In this pathway, an enzyme, Prolyl Hydroxylase Domain protein 2 (PHD2), constitutively prolyl hydroxylates HIF-2α, thereby targeting HIF-2α for degradation by the von Hippel Lindau (VHL) tumor suppressor protein. Under hypoxia, this modification is attenuated, resulting in the stabilization of HIF-2α and transcriptional activation of the erythropoietin (EPO) gene. Circulating EPO then binds to the EPO receptor (EPOR) on red cell progenitors in the bone marrow, leading to expansion of red cell mass. Loss of function mutations in PHD2 and VHL, as well as gain of function mutations in HIF-2α and EPOR, are well established causes of erythrocytosis. Here, we highlight recent developments that show that the study of this condition is still evolving. Specifically, novel mutations have been identified that either change amino acids in the zinc finger domain of PHD2 or alter splicing of the VHL gene. In addition, continued study of HIF-2α mutations has revealed a distinctive genotype-phenotype correlation. Finally, novel mutations have recently been identified in the EPO gene itself. Thus, the cascade of genes that at a molecular level leads to EPO action, namely PHD2 - > HIF2A - > VHL - > EPO - > EPOR, are all mutational targets in congenital erythrocytosis.