Hereditary spherocytosis

These disorders are caused by variants in the genes encoding the proteins of the red cell membrane and its underlying cytoskeleton. Loss of mechanical stability of this network causes the red cells to lose surface area and to be cleared prematurely.

HS is most often caused by variants in ANK1 (ankyrin), SPTB (beta-spectrin), SLC4A1 (band 3), SPTA1 (alpha-spectrin) and EPB42 (protein 4.2). A novel disease-causing SLC4A1 variant associated with HS has been characterised, illustrating the ongoing expansion of the known variant spectrum.

HE and HPP are most often caused by variants in SPTA1, SPTB and EPB41 (protein 4.1). In HE, variants in SPTA1 are the most common (reported in around 65% of cases), followed by SPTB (around 30%) and EPB41 (around 5%). HPP commonly arises when a spectrin variant is combined with a second, low-expression allele on the other copy of the gene (for example, a low-expression SPTA1 allele in trans to a pathogenic SPTA1 variant), which is why HPP and HE are so closely related at the molecular level.

The inheritance pattern differs between the conditions.

• Hereditary spherocytosis is predominantly inherited in an autosomal dominant manner so that an affected parent has, on average, a one in two chance of passing the predisposition to each child. A minority of cases are autosomal recessive, and these recessive forms (often due to biallelic SPTA1 variants) tend to be more severe; de novo (new) variants also occur.
• Hereditary elliptocytosis is mostly inherited in an autosomal dominant manner.
• Hereditary pyropoikilocytosis is inherited in an autosomal recessive manner, typically through biallelic variants or the combination of a pathogenic spectrin variant with a low-expression allele in trans.

Diagnosis begins with a full blood count, reticulocyte count, blood film review and markers of haemolysis (for example, raised bilirubin and lactate dehydrogenase, reduced haptoglobin), together with a direct antiglobulin test to exclude immune haemolysis. Characteristic red cell morphology (spherocytes in HS, elliptocytes in HE, fragmented poikilocytes in HPP) guides the initial assessment.

For HS, recommended confirmatory tests include the eosin-5-maleimide (EMA) binding test by flow cytometry and an osmotic-fragility-based assay such as the flow-cytometric osmotic-fragility test. Molecular genetic testing by next-generation sequencing (NGS) of a membrane-disorder gene panel is increasingly used to confirm the diagnosis, to clarify atypical or overlapping presentations, and to identify the causative variants. In several settings NGS is now performed early in the diagnostic pathway, before or alongside protein-based investigations.

Because the three in-scope conditions overlap, the main task is often to distinguish between them and from other causes of haemolytic anaemia. The differential diagnosis includes autoimmune haemolytic anaemia, which can also produce spherocytes and is excluded by a direct antiglobulin test. Other inherited causes of chronic haemolysis to consider include red cell enzymopathies (for example, glucose-6-phosphate dehydrogenase deficiency and pyruvate kinase deficiency), the haemoglobinopathies and thalassaemias, and other rarer membrane disorders such as the hereditary stomatocytoses. Atypical or borderline presentations may show overlapping morphology, which is one reason a gene panel covering all of these membrane-disorder genes is helpful.

Genetic testing using a membrane-disorder gene panel:

• supports a precise diagnosis where blood film morphology and protein-based tests are inconclusive or overlapping;
• supports the distinction between HS, HE and HPP, which share several causative genes;
• supports the identification of the underlying variant or variants, which can inform expectations about disease course and severity (for example, biallelic SPTA1 variants associated with more severe disease);
• supports family assessment and genetic counselling, including clarification of the inheritance pattern and recurrence risk once the causative variants are known.

• Bolton-Maggs PH, Langer JC, Iolascon A, Tittensor P, King MJ; General Haematology Task Force of the British Committee for Standards in Haematology. Guidelines for the diagnosis and management of hereditary spherocytosis, 2011 update. Br J Haematol. 2012;156(1):37-49. doi: 10.1111/j.1365-2141.2011.08921.x. PMID: .
• Chueh HW, Hwang SM, Shim YJ, Lee JM, Park HS, Lee JH, et al; Korean RBC Disorder Working Party. Korean clinical practice guidelines for the diagnosis of hereditary hemolytic anemia. Blood Res. 2022;57(2):86-94. doi: 10.5045/br.2022.2021224. PMID: .
• Chonat S, Risinger M, Sakthivel H, Niss O, Rothman JA, Hsieh L, et al. The spectrum of SPTA1-associated hereditary spherocytosis. Front Physiol. 2019;10:815. doi: 10.3389/fphys.2019.00815. PMID: .
• Kim Y, Park J, Kim M. Diagnostic approaches for inherited hemolytic anemia in the genetic era. Blood Res. 2017;52(2):84-94. doi: 10.5045/br.2017.52.2.84. PMID: .
• Kager L, Jimenez-Heredia R, Zeitlhofer P, Novak W, Eder SK, Segarra-Roca A, et al. A single-center cohort study of patients with hereditary spherocytosis in Central Europe reveals a high frequency of novel disease-causing genotypes. HemaSphere. 2024;8(1):e31. doi: 10.1002/hem3.31. PMID: .
• Bogusławska DM, Kraszewski S, Skulski M, Potoczek S, Kuliczkowski K, Sikorski AF. Novel variant of the SLC4A1 gene associated with hereditary spherocytosis. Biomedicines. 2023;11(3):784. doi: 10.3390/biomedicines11030784. PMID: .
• Han E, Kim A, Park J, Kim M, Kim Y, Han K, et al. Spectrin Tunis (Sp alpha I/78) in a Korean family with hereditary elliptocytosis. Ann Lab Med. 2013;33(5):386-9. doi: 10.3343/alm.2013.33.5.386. PMID: .