# The Progress in Treatment of \(\beta\)-Thalassemia and Research on Animal Models of the Disease
## 4 Animal Models of \(\beta\)-Thalassemia
### Mouse Models  
Mice have two genes, \(\beta^{\text{major}}\) and \(\beta^{\text{minor}}\), which are highly homologous; however, their expression levels in vivo differ significantly, with approximately 80% of adult hemoglobin being \(\alpha_{2}\beta_{2}^{\text{major}}\). The primary challenge faced by mouse models in simulating human hemoglobin disorders is the difference in hemoglobin switching frequency and developmental timing between humans and mice. Consequently, in recent decades, researchers have developed several mouse models of human \(\beta\)-thalasemia, which will be explored in detail in the following sections. The first mouse model developed for studying \(\beta\)-thalasemia was a spontaneous mutation characterized by reduced expression of the \(\beta^{\text{major}}\) gene. In this model, heterozygosity  
Figure 1: Summary of animal model classifications. This figure summarizes the current animal models for simulating \(\beta\)-thalasemia. NTDT = non-transfusion-dependent \(\beta\)-thalasemia; TDT = transfusion-dependent \(\beta\)-thalasemia; HBB = \(\beta\)-globin gene. Part of the figure is drawn using an image created with BioCDP.com. gous mice exhibited normal hematological parameters, while the surviving homozygous Hbbth1 mice displayed mild anemia that resembled non-transfusion-dependent thalassemia (NTDT) [41]. Although Hbbth1 mice can survive without the need for transfusions, their intestinal iron absorption rate is significantly increased [42]. However, iron accumulation within tissues continues to increase gradually. Specifically, iron deposition in Hbbth1 mice typically occurs before the age of 7 to 8 weeks, being confined to the liver, kidneys, and spleen, with no iron deposition observed in the heart [43]. Consequently, homozygous Hbbth1 mice are frequently utilized as an experimental model for this disease. Furthermore, [PERSON] et al. [44] found that Hbbth2 mice with the Hbb-b1 gene artificially disrupted by the insertion of a neomycin gene cassette did not exhibit a compensatory increase in \(\beta\) minor production. This lack of increase may be attributed to competition between the Hbb-b2 gene promoter and the targeting cassette, which interferes with the regulatory region of the \(\beta\)-globin gene. This mechanism causes heterozygous mice to exhibit mild anemia, whereas homozygous mutant mice experience a cessation of embryonic gene expression by gestation day 16.5, with the hemoglobin levels remaining extremely low by gestation day 18.5. Furthermore, blood smears reveal classic characteristics of severe thalassemia, showing almost no normal round red blood cells, evidence of hypochromia and poikilocytosis, and the presence of nucleated red blood cell precursors [44]. Typically, homozygous mutant mice die during late gestation or in the early postnatal period, which limits the applicability of this model in subsequent research. The most widely used mouse model for non-transfusion-dependent \(\beta\)-thalasemia is the Hbbth3 mouse, characterized by a single copy deficiency of the Hbb-b1 and Hbb-b2 genes [45]. This model exhibits all the key characteristics of non-transfusion-dependent \(\beta\)-thalasemia, including severe anemia, abnormal erythrocyte morphology, ineffective erythropoiesis, and iron overload. To address the diverse pathophysiological characteristics of this disease, researchers are actively investigating combination therapies. These therapies involve the use of iron transport protein inhibitors and hepcidin activators to alleviate anemia and improve ineffective erythropoiesis. Consequently, the Hbbth3 mouse is considered the preferred model for severe non-transfusion-dependent \(\beta\)-thalasemia and has been extensively utilized in preclinical research [45]. While current mouse models effectively replicate certain pathological characteristics of \(\beta\)-thalasemia, their utility in correcting specific gene mutations or reactivating \(\gamma\)-globin remains constrained.