Overhydrated stomatocytosis associated with a complex RHAG genotype including a novel de novo mutation

Overhydrated stomatocytosis is a rare autosomal dominant disorder known to cause variably severe haemolytic anaemia due to heterozygous mutations in the RHAG gene. We report a 26-year-old man with recurring jaundice, splenohepatomegaly and mild chronic haemolytic anaemia with significant stomatocytosis. Extensive haemolytic work-up including flow cytometry for eosin-5′-maleimide and CD47 expression levels was carried out. Targeted resequencing revealed two probably causative heterozygous mutations in RHAG (Leu336Ser and Ile149Met) and one heterozygous mutation in ANK1 (Glu1046Lys) . RHAG involvement was confirmed by decreased RhAG macrocomplex component indicated by the reduced CD47 expression on erythrocytes. In silico analysis concordantly flagged RHAG :Leu336Ser and ANK1 :Glu1046Lys as likely deleterious mutation, whereas RHAG :Ile149Met was reported as likely neutral by PROVEAN. Family screening by Sanger sequencing revealed RHAG :Leu336Ser in a mother and ANK1 :Glu1046Lys in a father who were both asymptomatic, excluding them as causative dominant events, thus establishing RHAG :Ile149Met, novel de novo mutation as probably causative. This case illustrates the importance of family screening in interpreting next-generation sequencing (NGS) data, as in silico analysis alone can be misleading. Erudite generation of diagnostic possibilities based on a thorough baseline clinical and laboratory work-up remains as important as ever, even as NGS brings about a paradigm shift in the diagnostic work-up of rare haemolytic anaemias.