Hereditary Erythrocytosis Panel, Sequencing

Use to assess for inherited/germline DNA variants associated with familial/hereditary erythrocytosis

Erythrocytosis (ECYT) is characterized by an overproduction of red blood cells (RBCs), which leads to elevated hemoglobin and hematocrit levels. Symptoms may include headaches, dizziness, dyspnea, and epistaxis. The overabundance of RBCs may lead to hemorrhagic or thrombotic events, including myocardial infarction and deep vein thrombosis, although many individuals with ECYT experience mild symptoms and may be asymptomatic.

Hereditary ECYT, also known as familial ECYT or congenital polycythemia, is a group of disorders in which ECYT is caused by inherited/germline pathogenic variants.

Genetics

ECYT can be categorized as primary ECYT, caused by pathogenic variants leading to intrinsic defects in hematopoietic stem cells that increase RBC production, or secondary ECYT caused by pathogenic variants that drive RBC production by increasing erythropoietin (EPO) levels. Hereditary ECYT is suspected when acquired ECYT (either primary or secondary) has been excluded in an individual, and hereditary ECYT is suspected in those with early age of onset or a family history of ECYT.

See Genes Tested table for genes included in the panel, associated disorders, and inheritance.

Genes Tested

Gene MIM # Disorders Inheritance

BPGM

613896

Secondary ECYT

Familial ECYT 8 (ECYT8)

AR

EGLN1 (PHD2)

606425

Secondary ECYT

Familial ECYT 3 (ECYT3)

AD

EPAS1 (HIF2A)

603349

Secondary ECYT

Familial ECYT 4 (ECYT4)

AD

EPOR

133171

Primary ECYT

Familial ECYT 1 (ECYT1)

AD

HBB

141900

Secondary ECYT

High oxygen affinity hemoglobin variants

Familial ECYT 6 (ECYT6)

AD

Beta thalassemia

Sickle cell anemia

AR

HIF1A

603348

Secondary ECYT

Unknown

JAK2

147796

Hereditary thrombocytosis

AR

Polycythemia vera

Myelofibrosis

ECYT

Somatic

SH2B3

605093

Primary ECYT

Unknown

ECYT

Myelofibrosis

Thrombocythemia

Somatic

VHL

608537

Secondary ECYT

Familial ECYT 2 (ECYT2), Chuvash polycythemia

AR

von Hippel-Lindau syndrome (VHL) AD

AD, autosomal dominant; AR, autosomal recessive

Test Interpretation

Methodology

This test is performed using the following sequence of steps:

  • Selected genomic regions, primarily coding exons and exon-intron boundaries, from the targeted genes are isolated from extracted genomic DNA using a probe-based hybrid capture enrichment workflow.
  • Enriched DNA is sequenced by massively parallel sequencing (MPS; also known as next generation sequencing [NGS]) followed by paired-end read alignment and variant calling using a custom bioinformatics pipeline.
  • Sanger sequencing is performed as necessary to fill in regions of low coverage and in certain situations, to confirm variant calls.

Sensitivity and/or Specificity

Clinical Sensitivity

Approximately 30% (up to 70% of cases of hereditary ECYT have no identifiable cause and are considered idiopathic ECYT)

Analytic Sensitivity

Variant Class Analytic Sensitivity (PPA) Estimatea (%)
and 95% Credibility Region (%)
Analytic Specificity (NPA) Estimate (%)

SNVs

>99 (96.9-99.4)

>99.9

Deletions 1-10 bpb

93.8 (84.3-98.2)

>99.9

Insertions 1-10 bpb

94.8 (86.8-98.5)

>99.9

aPPA values are derived from larger methods-based MPS and/or Sanger validations.

bVariants greater than 10 bp may be detected, but the analytic sensitivity may be reduced.

bp, base pairs; NPA, negative percent agreement; PPA, positive percent agreement; SNVs, single nucleotide variants

Limitations

  • A negative result does not exclude a diagnosis of ECYT.
  • Diagnostic errors can occur due to rare sequence variations.
  • Interpretation of this test result may be impacted if this patient has had an allogeneic stem cell transplantation, unless the sample analyzed is definitively from the recipient, such as cultured skin fibroblasts.
  • The following will not be evaluated:
    • Variants outside the coding regions and intron-exon boundaries of targeted genes
    • Regulatory region and deep intronic variants
    • The following exons are not sequenced due to technical limitations of the assay:
      • VHL (NM_001354723) exon 2
    • Large deletions/duplications in any of the tested genes
  • The following may not be detected:
    • Deletions/duplications/insertions of any size by MPS
    • Some variants due to technical limitations in the presence of pseudogenes and/or repetitive or homologous regions
    • Low-level somatic variants
  • The germline or somatic status of a detected variant cannot be definitively determined in patients with acquired ECYT or hematologic malignancy if the assay is performed on blood or other tissue that may be contaminated by clonal or malignant cells; testing a definitively germline specimen such as cultured fibroblasts may be recommended in such cases.
Additional Resources