Expanded Diagnostics: Focus on Membrane and Enzyme Disorders in Erythrocytes

The genetics of classical hematology includes hereditary anemias, familial erythrocytoses, and cyclic neutropenias. The most common disorders in this spectrum include hemoglobinopathies (such as thalassemias and sickle cell disease), membrane disorders (e.g., hereditary spherocytosis), and enzyme deficiencies (e.g., pyruvate kinase and G6PD deficiency).

Since early 2023, hemoglobinopathy diagnostics have been a core part of our service spectrum. We are now deliberately expanding this offer with additional tests. Newly added are diagnostic procedures for erythrocyte membrane and enzyme disorders.

For detecting hereditary spherocytosis, current guidelines from the Association of the Scientific Medical Societies in Germany (AWMF) and Onkopedia [1,2] recommend combining a flow cytometric EMA test with a method to determine erythrocyte osmotic fragility (e.g., AGLT-/PINK-test). Since March, we have routinely offered the PINK- (AGLT-) test for cases with suspected erythrocyte membrane defects.

In cases of unclear or negative results with ongoing clinical suspicion of a membrane disorder, molecular genetic analyses can be performed to identify causative genetic variants. Genetic confirmation is particularly important prior to therapeutic interventions, such as splenectomy.

Detection of pyruvate kinase deficiency is primarily performed molecularly, in accordance with current international expert guidelines [3]. In unclear genetic cases, measuring enzyme activity in purified erythrocytes can provide additional diagnostic insight.

For G6PD deficiency, we also offer both enzyme activity measurement and molecular genetic analysis of the G6PD gene. The recently published WHO G6PD variant classification [4] supports structured interpretation of genetic variants.

Important Note on Pre-Analytics: Please note that enzyme measurements can be influenced by pre-analytical factors (e.g., transport time, sample stability) as well as pathophysiological conditions (e.g., reticulocytosis during hemolysis). This should be considered when interpreting results.

For still unresolved cases with suspected inherited anemias, we currently offer whole genome sequencing (WGS) within the framework of a study in the Genomnetzwerk Hämatologie (Hematology Genome Network) [5] to comprehensively identify causes. Initial results indicate that causative variants can be detected in more than one-third of enrolled patients using WGS.

This approach aligns with current national WGS initiatives, demonstrating that comprehensive, unbiased genome analysis can significantly shorten the diagnostic process and identify both known and novel disease-causing variants. By integrating these methods into routine diagnostics, we aim to increase diagnostic yield and enable more precise genetic counseling and therapeutic recommendations.

For functional tests (PINK test, PK, and G6PD activity), 5 mL of EDTA blood is required. Samples should arrive at the lab within 48 hours of collection. For additional molecular genetic analyses, an additional 5 mL of EDTA blood is needed.

Important note: Please include a patient-signed consent form according to GenDG with all submissions, as genetic analysis is indicated in most cases.

With
the expansion of our diagnostic spectrum, we can now support you even more
precisely in the differential diagnosis of inherited anemias. For professional
questions or guidance on diagnostic procedures, Dr. Armin Piehler, MD PhD, is
available. Additional information is also available on our website.