Expanding the genetic landscape of SLC4A1-linked hereditary spherocytosis: discovery of a novel TM9 variant using high-resolution genomic profiling analysis

Abstract

Hereditary spherocytosis (HS) is the most common inherited red cell membranopathy caused by defects in erythrocyte membrane and cytoskeletal proteins, including ankyrin, spectrin, band 3, and protein 4.2. Among these, mutations in SLC4A1, which encodes the erythrocyte anion exchanger band 3 (AE1), account for approximately 20–30% of HS cases and it is associated with distal renal tubular acidosis (dRTA), reflecting phenotypic and functional heterogeneity. In this study, seven unrelated Indian patients with clinically suspected HS were investigated using detailed hematological, biochemical, and clinical evaluations along with eosin-5′-maleimide (EMA) binding assays. Molecular analysis was performed using targeted next-generation sequencing (t-NGS) covering 81 genes associated with red cell disorders, and the identified SLC4A1 variants were validated by Sanger sequencing. The structural and functional consequences of the variants were assessed through in silico tools including DynaMut, PolyPhen-2, and SIFT. Seven SLC4A1 variants were identified, including six previously reported variants and one novel variant, p.Phe702Ser, detected in heterozygous or compound heterozygous states. These variants were distributed across both cytoplasmic and transmembrane domains of the band 3 protein. Most patients presented with mild to moderate HS characterized by anemia, jaundice, splenomegaly, reticulocytosis, and reduced EMA fluorescence. One patient harboring compound heterozygous variants (p.Arg490His and p.Ala858Asp) exhibited HS associated with dRTA, highlighting the functional diversity of SLC4A1 mutations. The novel p.Phe702Ser variant, located in the transmembrane domain TM9, was predicted to destabilize AE1 structure and potentially impair anion transport. Marked intrafamilial phenotypic variability was observed despite identical genotypes. These findings expand the mutational spectrum of SLC4A1-related HS in Indian patients.