Difficult Cases in the Diagnosis of Thalassemia Syndromes.

Abstract

Thalassemia syndromes result from a significant reduction in the synthesis of globin chains (α, β, γ, δ). An imbalance between α- and non-α-globin chains underlies β-thalassemia. α-Globin tetramers accumulate and precipitate in erythroid precursors (ineffective erythropoiesis). Hemolysis also plays an important role, shortening the erythrocyte lifespan. α-Thalassemia syndromes are caused by approximately 200 deletions and point mutations, as well as rare large deletions. More than 350 mutations have been identified in β-thalassemia syndromes, the majority of which are point mutations, with rare large gene deletions. Molecular genetic diagnostic methods include the amplification refractory mutation system (ARMS), reverse dot blot (RDB) for known mutations, Gap-PCR, multiplex ligation-dependent probe amplification (MLPA) for unknown deletion mutations, and Sanger sequencing for point mutations. In recent years, next-generation sequencing (NGS) methods such as targeted panel tests allow rapid, high-throughput detection of genetic variants; whole exome sequencing (WES) and whole genome sequencing (WGS) are also used. We use a diagnostic algorithm in our center as follows: β sequencing, α MLPA, α sequencing, β MLPA. If a diagnosis cannot be made with these tests, we use an anemia panel containing 214 genes, WES, or WGS. In this study, we present difficult cases encountered at our center and discuss methods used for cases with genetic diagnostic challenges reported in the literature.