Spherocytosis/Elliptocytosis Panel

Hereditary Spherocytosis (HS), also known as Minkowski-Chauffard disease, is the most common form of hemolytic anemia due to red blood cell membrane defects. HS is a condition where red blood cells lose their hallmark biconcave disc shape leading to formation of spherocytes. Spherocytes have impaired flexibility making it difficult for red blood cells to transverse narrow capillaries, especially in the spleen. This impairment causes anemia due to chronic extravascular hemolysis resulting in jaundice, hyperbilirubinemia, gallstones, reticulocytosis and splenomegaly (Aster et al. 2013; An et al. 2008. PubMed ID: 18341630). Disease severity ranges with 20-30% of HS patients having mild, 60-70% having moderate, and 10-20% having severe forms of HS. Autosomal dominant HS typically result in mild to moderate HS compared to recessive HS primarily being moderate to severe. People with mild forms may be asymptomatic whereas severe forms of the disease present in newborns with severe anemia requiring blood transfusions. There are five types of HS defined by the causative gene for disease: Type I-ANK1, type 2-SPTB, type 3-SPTA1, type 4-SLC4A1, and type 5-EPB42 (Bolton-Maggs et al. 2012. PubMed ID: 22055020; Delaunay. 2007. PubMed ID: 16730867). HS affects one per 2,000 individuals.

Hereditary Elliptocytosis (HE) is a milder red blood cell membrane disorder affecting one in 5,000 individuals and is most commonly found in individuals of African, Mediterranean or Southeast Asian descent (Nagel and Roth. 1989. PubMed ID: 2669996). Red blood cells in these patients are elongated into an oval shape with flexibility being impaired less than individuals with HS. Subtypes of HE include hereditary pyropoikilocytosis (HPP) and Southeast Asian ovalocytosis (SAO). The majority of patients are asymptomatic with a few having moderate to severe anemia and intermittent episodes of hemolysis, jaundice, and splenomegaly. Symptoms may present at 4-6 months in severe cases but usually resolve by 6-12 months. Newborns with HPP often present with hemolytic anemia and require frequent blood transfusions. Individuals with SAO present with a stomatocytic elliptocytosis red blood cell morphology and may exhibit mild anemia. About half of SAO neonates present with hyperbilirubinemia which resolves in early childhood (Laosombat et al. 2010. PubMed ID: 20421175).

Elliptocytosis and spherocytes have been reported in other disorders including iron deficiency, leukemia, megaloblastic anemia, myelofibrosis, sickle cell disease, thalassemia, and polycythemia therefore genetic testing is helpful in differential diagnosis (Gallagher. 2004. PubMed ID: 15071791).

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 commonly found 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 et al. 2008. PubMed ID: 18341630). About 30% of HS cases are sporadic with no family history.

HE is inherited in an autosomal dominant manner via the SPTA1 (65% of cases), SPTB (30% of cases), or EPB41 (5% of cases) genes. HPP is caused by homozygous recessive or compound heterozygous variants in the SPTA1 gene (Gallagher. 2004. PubMed ID: 15071791). A 27bp deletion in the SLC4A1 gene, denoted c.1199_1225del (p.Ala400_Ala408del), is a founder variant frequently found in patients with SAO (Laosombat et al. 2010. PubMed ID: 20421175). Autosomal recessive HS is also inherited via the SPTB, EPB41, and EPB42 genes.

The ANK1, SPTB, SLC4A1, SPTA1, EPB42 and EPB41 genes encode proteins that help to maintain the biconcave disc morphology in red blood cells through connections between the spectrin cytoskeleton and membrane proteins (Bolton-Maggs et al. 2012. PubMed ID: 22055020).

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

In a study of HS patients of Korean descent, pathogenic variants in the ANK1 or SPTB genes were identified in 21 of 25 patients with over half of the cases being de novo (Park et al. 2016. PubMed ID: 26830532). A separate study identified causative pathogenic variants in 50 of 59 HS patients using an NGS panel approach (Choi et al. 2019. PubMed ID: 31122244). Analytical sensitivity is >95%.

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

This panel provides 100% 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).

Sequencing will also cover 500 bp upstream of the ANK1 start codon and the SPTA1 Lepra/Prague region, c.4339-99C>T (Miraglia del Giudice et al. 2001. PubMed ID: 11167781).

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).