Hereditary Hemolytic Anemia Panel

Hemolytic anemia is caused by premature destruction of red blood cells (RBC). This can be cause by both intrinsic factors such as inherited conditions or extrinsic factors such as autoimmunities, drugs, microangiopathies, and hypersplenism. Intrinsic hemolytic anemias are largely divided into three categories: hemogloblinopathies, erythrocyte membrane defects and enzyme deficiencies. Hemoglobinopathy testing is available separately and not included in this panel due to different testing methodologies. The most common erythrocyte membrane defect is hereditary spherocytosis which affects 1 in 2,000 individuals. Other erythrocyte membrane defects include elliptocytosis, stomatocytosis, ovalocytosis and pyropoikilocytosis (An and Mohandas. 2008. PubMed ID: 18341630). With red blood cells relying on the glycolytic pathway for ATP production, several enzyme defects in this pathway are associated with hemolytic anemia. Glucose-6-phosphate dehydrogenase deficiency is the most prominent enzyme deficiency affecting over 400 million people worldwide. Congenital dyserythropoietic anemia (CDA) also shares some clinical characteristics of hemolytic anemia (Iolascon et al. 2012. PubMed ID: 23940284). Hemolytic anemia severity can range from asymptomatic mild hemolysis to life threatening severe hemolysis with onset at birth. Genetic testing can be helpful for differential diagnosis of intrinsic versus extrinsic forms of hemolytic anemia and for accurate diagnosis of intrinsic hemolytic anemia (Kim et al. 2017. PubMed ID: 28698843; Risinger et al. 2019. PubMed ID: 31030808).

Hereditary spherocytosis (HS) in inherited in an autosomal dominant manner in 75% of cases through pathogenic variants in the ANK1, SPTB, and SLC4A1 genes. Autosomal recessive forms are primarily inherited through pathogenic variants in the SPTA1 gene (Bolton-Maggs et al. 2012. PubMed ID: 22055020). A founder variant in Eastern Europeans, designated c.4339-99C>T or Lepra, is the most common pathogenic variant in the SPTA1 gene. In general, truncating variants in the SPTB gene are associated with autosomal dominant forms of HS, whereas missense variants are more commonly found in autosomal recessive forms. Most pathogenic variants reported to date in HS related genes are private truncating variants (Park. 2016. PubMed ID: 26830532; Wang. 2018. PubMed ID: 29572776). Pathogenic variants in the ANK1, SPTB, SLC4A1, SPTA1, and EPB42 genes account for 60%, 10%, 15%, 10%, and 5% cases of HS respectively (An and Mohandas. 2008. PubMed ID: 18341630). About 30% of HS cases are de novo with no family history. Copy number variants have only been reported in a few cases.

Red blood cell enzymopathies are due to defects in genes in the glycolytic pathway. These disorders are inherited in an autosomal recessive manner through pathogenic variants in the AK1, ALDOA, GCLC, GPI, GPX1, GSR, GSS, HK1, NT5C3A, PFKL, PFKM, PKLR, and TPI1 genes and through an X-linked manner through the G6PD and PGK1 genes. Pathogenic variants in the G6PD and PKLR genes represent the most common red blood cell enzymopathies with missense changes being most frequent: ~85% and ~70% respectively (Kim et al. 2017. PubMed ID: 28698843; Risinger et al. 2019. PubMed ID: 31030808). Both hemizygous males and homozygous females have been reported with glucose-6-phosphate dehydrogenase deficiency. The majority of G6PD variants are founder variants which were selected due to providing protection from malarial infections (Kim et al. 2017. PubMed ID: 28698843).

Congenital dyserythropoietic anemia (CDA) is inherited in an autosomal recessive manner through pathogenic variants in the CDAN1, CDIN1/C15ORF41, and SEC23B genes, in an autosomal dominant manner through pathogenic variants in the KLF1 and KIF23 genes, and in an X-linked manner through the GATA1 gene. Type II CDA, the most common form with about 450 cases worldwide, is characterized by mild to severe anemia through pathogenic variants in the SEC23B gene (Iolascon et al. 2012. PubMed ID: 23940284). Copy number variants have rarely been reported in patients with CDA.

Hereditary xerocytosis (HX) or dehydrated stomatocytosis is inherited in an autosomal dominant manner through pathogenic variants in the PIEZO1 and KCNN4 genes. Gain of function missense variants in the PIEZO1 gene results in increased permeability of cations resulting in HX (Albuisson et al. 2013. PubMed ID: 23695678; Andolfo et al. 2013. PubMed ID: 23479567).

See individual gene and/or panel summaries for more information about molecular biology of gene products and spectra of pathogenic variants.

In a series of 195 cases of hereditary hemolytic anemia in Korea, 192 patients had positive genetic findings with erythrocyte membrane defects, hemoglobinopathies, and enzyme deficiencies representing 64.8%, 19.9% and 13.3% of cases (Park et al. 2013. PubMed ID: 24086942). In a separate study of 17 individuals, including patients with extreme hyperbilirubinemia or transfusion dependent, a genetic diagnosis was achieved in 12 cases with erythrocyte membrane defects being most prevalent (Agarwal et al. 2016. PubMed ID: 27292444).

This test is performed using Next-Gen sequencing with additional Sanger sequencing as necessary.

This panel typically provides 99.8% coverage of all coding exons of the genes plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define coverage as ≥20X NGS reads or Sanger sequencing. PGnome panels typically provide slightly increased coverage over the PGxome equivalent. PGnome sequencing panels have the added benefit of additional analysis and reporting of deep intronic regions (where applicable).

Dependent on the sequencing backbone selected for this testing, discounted reflex testing to any other similar backbone-based test is available (i.e., PGxome panel to whole PGxome; PGnome panel to whole PGnome).