Hereditary Spherocytosis via the EPB42 Gene

Hereditary Spherocytosis (HS), also known as Minkowski-Chauffard disease, affects one in 2,000 individuals. HS is a condition where red blood cells lose their typical biconcave disc shape and appear spherical. The spherical shape impairs membrane flexibility making it hard for red blood cells to transverse narrow capillaries, especially in the spleen. This impairment causes anemia due to chronic extravascular hemolysis, jaundice, formation of bilirubin gallstones, reticulocytosis and splenomegaly (Aster et al. 2013; An and Mohandas 2008). Disease severity can range with 20-30% having mild form, 60-70% having moderate form, and 10-20% having severe form of HS. People with mild forms may be asymptomatic whereas severe forms of the disease present in newborns with life threatening anemia and require blood transfusions. There are five types of HS defined by the gene mutation causative for disease: Type I-ANK1, type 2-SPTB, type 3-SPTA1, type 4-SLC4A1, and type 5-EPB42 (Bolton-Maggs et al. 2004; Delaunay 2007). Type 5 HS makes up less than 5% of cases and is predominantly found in Japanese.

HS in inherited in an autosomal dominant manner in 75% of cases through mutations in the ANK1, SPTB, and SLC4A1 genes. Autosomal recessive forms are inherited through mutations in the ANK1, SPTA1, and EPB42 genes (Bolton-Maggs et al. 2004). Most mutations reported to date are private with de novo dominant mutations being six times more common than recessive mutations (Miraglia del Giudice et al. 2001). Mutations 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). HS type 5 is inherited through an autosomal recessive manner through mutations in the EPB42 gene. Causative mutations are predominantly missense leading to impaired protein stability and a loss of Protein 4.2. Splicing mutations and small deletions make up the minority of cases (An and Mohandas 2008; Bolton-Maggs et al. 2004). Gross deletions have not been reported to date. Alpha thalassemia through mutations in the HBA1 and HBA2 genes has been shown to coexist within patients with EPB42 mutations with both diseases contributing to anemia (Maciaq et al. 2009). The EPB42 gene encodes for Protein 4.2 which is an anchoring protein linking ankryin and specrin to the membrane. These interactions are critical for maintaining the hallmark biconcave disc morphology of red blood cells and providing elasticity to navigate narrow vasculature (An and Mohandas 2008).

Mutations in the EPB42 gene are causative for <5% of HS. Analytical sensitivity should be high as all mutations reported to date are detected by NextGen sequencing (An and Mohandas 2008).

This test provides full coverage of all coding exons of the EPB42 gene 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 full 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).