P1472: coinheritance of piezo1 variants and multi-locus red blood cell defects account for the symptomatic phenotype in beta-thalassemia carriers.

Topic: 28. Enzymopathies, membranopathies and other anemias Background: Approximately 1-5% of the global population is a carrier of a thalassemia mutation. Carriers of β-thalassemia, also defined as beta thalassemia trait (BT), are generally asymptomatic with mild, microcytic hypochromic anemia. We herein described a cohort of BT carriers presenting with anemia of variable degree, splenomegaly, alteration in hemolysis indices, and liver hemosiderosis (referred as symptomatic BT) analyzed for second- and third-line investigation in the suspicion of others erythrocyte defects. Aims: The aim of the study was to evaluate if the combination of the BT and other inherited RBC disorders could account for phenotypic variability. Methods: A cohort of 20 symptomatic BT carriers from 16 unrelated families followed in the specialized center for congenital anemias of Genoa (Italy) were analyzed for the diagnosis of RBC defects at the Medical Genetic Unit of AOU Federico II/CEINGE, Naples from November 2019 to December 2022 and they were compared to a cohort of BT carriers (n = 53) without anemia, alteration of hemolysis indices and iron parameters identified during a carrier screening for hemoglobinopathies. All the symptomatic BT patients were investigated by family history, blood count, peripheral blood smear, ektacytometry curve, molecular testing for HBB/HBA, next-generation sequencing for Hereditary Anemia (HA). Results: Among 20 BT symptomatic patients, we found causative variants of HA in 15/20 (75%). Overall, 66.7% (10/15) showed monogenic HA in addition to BT, while 33.3% (5/15) showed multi-locus HA. Of note, 14 out 15 symptomatic BT carriers showed mutations in PIEZO1 gene. The variants found in BT patients were classified by automated ACMG rule and then outputs were adjusted using additional available evidence for each patient, as well as data from literature studies and from in-house cohort of DHS patients. Additional analysis as PB smear evaluation revealed the presence of abnormal morphology. Similarly, the ektacytometry curves revealed alterations in all the 15 symptomatic BT patients compared to both healthy controls and asymptomatic BT. Overall, the clinical features of BT carriers with associated HA demonstrated the presence of splenomegaly in 87% (13/15), alteration in hemolysis indices in 73% (11/15), anemia in 100% (15/15). Analysis of the complete blood count showed decreased levels of both RBC count and Hb levels in symptomatic BT carriers with HA compared to asymptomatic subjects. On the contrary, the reticulocytes count resulted slightly increased in symptomatic BT carriers compared to the symptomatic ones. Of note, symptomatic BT carriers showed markedly increased hemolysis signs compared to asymptomatic BT subjects. Interestingly, no difference of the mean corpuscular volume (MCV) between the two groups was observed. Summary/Conclusion: The analysis of the present cohort of patients demonstrated that the clinical phenotype was more severe for BT carriers with dehydrated hereditary stomatocytosis, or multi-locus inheritance compared to pure BT carriers in terms of Hb levels, splenomegaly, and hemolytic indices. Our study highlighted the importance to investigate those cases of BT carriers in which the heterozygosity for a HBB variant is not enough to explain the entire clinical phenotype, even if the association of BT trait with RBC defects is a rare condition. This allows to underline that coinheritance of BT and RBC defects should be considered as part of thalassemic syndromes because these patients should be treated as NTDT or TDT thalassemic patients in terms of management and therapeutic treatment options Keywords: Red blood cell, Hemoglobinopathy, beta thalassemia, Genetic modifiers