Clinical and Genetic Study of Hereditary Spherocytosis in the Spanish Population

Background: Hereditary spherocytosis (HS) is the most common congenital hemolytic anemia (CHA) affecting 1/2000 individuals of European descent. Pathogenic mutations have been described in 5 genes encoding red cell membrane and cytoskeleton proteins: ANK1 (ankyrin), SPTB(β-spectrin), SPTA1(α-spectrin), SLC4A1(band-3) and EPB42(protein 4.2). The clinical phenotype is very heterogeneous, ranging from asymptomatic compensated hemolysis to transfusion dependence. Seventy percent of HS are inherited autosomal dominantly, 10% recessively and the rest are de novo mutations.

Aims: To describe a large population of patients with diagnosis of hereditary spherocytosis, confirmed by a genetic study. To study the genotype-phenotype relationship in our patients.

Methods: Multicenter retrospective study of patients followed up in 11 Spanish hospitals between 1990 and 2022. Patients initially presented suspicion of HS based on family history and laboratory data (decreased RGO, elevated % of hyperchromes, spherocytes in the smear and biochemical data of hemolysis). A molecular study by NGS with congenital hemolytic anemia panel was later performed in all patients to confirm de diagnosis. The research of the genetic variants found was carried out in the Franklin and Varsome (Clinvar) databases. The authors declare no conflict of interest.

Results: Molecular studies were performed in 145 patients and clinical data is available for 75 patients. 55% were females. The average age was of 29 years old (10-49). The most frequent mutations were in SPTB and ANK1. We have found 61 known variants and 84 new variants. The patients in our series had mild spherocytosis and 71% of them had a family history of this pathology. Comparing patients who have a variant described as pathogenic versus those who have a variant that is probably pathogenic or of uncertain significance, we have found the following: both groups have similar hemoglobin levels; patients with pathogenic mutations have higher reticulocyte levels and lower haptoglobin numbers; but the only statistically significant difference between the two groups is the percentage of hyperchromic red cells (p<0.05). Due to the small sample size, we found no differences in the number of splenectomies or cholecystectomies between the different genetic alterations.

Conclusions: In our study, the most frequently found mutations were SPTB, followed by mutations in ANK and SLC4A1. We found a very high incidence of new HS gene variants not described in the literature. We have not been able to establish a correlation between the different genetic mutations and the clinical expressivity of the disease. Moreover, further studies are needed to establish the pathogenicity of variants of uncertain significance and correlate them with the patients' phenotype. Molecular study of patients with suspected HS has important implications for genetic counseling: it can be transcendental in the therapeutic approach, especially in the choice of splenectomy, as well as to avoid severe forms through family and prenatal study. It is necessary to establish the profile of patients for molecular studies and to have a larger number of patients to adequately establish the phenotype-genotype correlation.

Villegas:Agios: Consultancy.