Genetic analysis of 39 erythrocytosis and hereditary hemochromatosis-associated genes in the Slovenian family with idiopathic erythrocytosis

Abstract

Background: Erythrocytosis is a condition with an excessive number of erythrocytes, accompanied by an elevated haemoglobin and/or haematocrit value. Congenital erythrocytosis has a diverse genetic background with several genes involved in erythropoiesis. In clinical practice, nine genes are usually examined, but in approximately 70% of patients, no causative mutation can be identified. In this study, we screened 39 genes, aiming to identify potential disease-driving variants in the family with erythrocytosis of unknown cause.

Patients and methods: Two affected family members with elevated haemoglobin and/or haematocrit and negative for acquired causes and one healthy relative from the same family were selected for molecular-genetic analysis of 24 erythrocytosis and 15 hereditary haemochromatosis-associated genes with targeted NGS. The identified variants were further analysed for pathogenicity using various bioinformatic tools and review of the literature.

Results: Of the 12 identified variants, two heterozygous variants, the missense variant c.471G>C (NM_022051.2) (p.(Gln157His)) in the EGLN1 gene and the intron variant c.2572-13A>G (NM_004972.3) in the JAK2 gene, were classified as low-frequency variants in European population. None of the two variants were present in a healthy family member. Variant c.2572-13A>G has potential impact on splicing by one prediction tool.

Conclusion: For the first time, we included 39 genes in the erythrocytosis clinical panel and identified two potential disease-driving variants in the Slovene family studied. Based on the reported functional in vitro studies combined with our bioinformatics analysis, we suggest further functional analysis of variant in the JAK2 gene and evaluation of a cumulative effect of both variants.

Keywords: DNA; erythrocytosis; genetic variation; haemochromatosis; sequence analysis.

FIGURE 1

Identification of a heterozygous nucleotide variants in the EGLN1 and JAK2 genes (A) Family pedigree and segregation of the variants identified within the family. (B) Next‐generation sequencing (NGS) and (C) Sanger sequencing, showing heterozygous EGLN1 variant in the two affected patients , but not in the unaffected family member. (D) Results of NGS showing intron variant in the JAK2 gene in both of the affected family members, but not in the unaffected family member. Squares, circles, represent males, females, respectively. Filled symbols, patients with clinical diagnosis of erythrocytosis; open symbols, unaffected family members; slashed symbol, subject is deceased. Carriers of heterozygous EGLN1 and JAK2 variants are indicated as ‐/M. Arrow indicates mutation point