Hereditary spherocytosis associated with Noonan syndrome mimicking a dyserythropoietic anaemia

To the Editor: Congenital dyserythropoietic anaemias (CDAs) are rare hereditary disorders characterised by ineffective erythropoiesis, chronic haemolytic anaemia, distinctive bonemarrow features of the erythroid precursors, and risk of secondary haemochromatosis.1 Four types of CDA and CDA variants have been described along with their causal mutated genes (CDAN1, C15ORF41, SEC23B, KIF23, RACGAP1, KLF1, GATA-1).2–10 Despite marrow CDA features, some patients have no relevant mutation with previous Sanger or targeted next-generation sequencing (NGS), and whole-exome sequencing (WES) or wholegenome sequencing (WGS) might allow identification of the allelic variant. The case reported here concerns a child born in Chechnya at term with average weight and length. He is the third child of a healthy non-consanguineous couple with healthy brothers and no history of anaemia in the family. During his first week of life, he had jaundice attributed to ABO incompatibility. From the age of 5 months, he developed pallor, jaundice and splenomegaly. Haematologic evaluation performed at 3 years old confirmed anaemia and hyperbilirubinemia with some haemolytic markers. Hereditary spherocytosis (HS) was initially suspected but not validated as the osmotic fragility testwas negative and ektacytometrywas not performed at the time. At 8 years of age, the patient was referred to our institution for further investigation in the context of jaundice, severe splenomegaly and growth delay. Both height and weight were under –2 SD, and no dysmorphic features, intellectual disability, cardiac or urogenital malformations were noted. The laboratory assessment is summarised in Table 1. Coombs test, erythrocytic enzymes, haemoglobin electrophoresis and cryohaemolysis test were normal and α deletion was ruled out. The blood smear showed poikilocytosis with no spherocytes (Figure 1A), and the marrow was hypercellular and dyserythropoietic (Figure 1B). No sideroblasts were seen after Perls prussian blue stain. The analysis of red cell membrane proteins by sodium polyacrylamide gel electrophoresis was inconclusive, whereas Sanger sequencing of the CDA genes, performed in 2016 before NGS availability, identified two heterozygous variants in KIF23 (NM_138555:c.690A>G, p.(Ile230Met)) and CDAN1 (NM_138477.2:c.1967C>G, p.(Thr656Ser)). Although these allelic variants were likely benign according to international recommendations,11 a diagnosis of CDA was suggested based on the associated clinical manifestations and dyserythropoiesis in the bone marrow, more than onmolecular results. Endocrinological assessment performed at 13 years old showed impaired growth hormone (GH) response and low morning cortisol level with poor response after glucagon test, evoking a partial GH and corticotropin deficiency. At 16 years of age, the patient developed hypersplenism with abdominal discomfort, mild leukopenia and thrombocytopenia. A splenectomy was performed and followed by the normalisation of blood count (Table 1). Because of the absence of an unequivocal molecular diagnosis of CDA, we pursued the assessment of our patient and relatives (supporting information): at the age of 18, targeted NGS revealed a de novo heterozygous variant located in the canonical splice site of intron 4 of the SPTB gene (NM_001024858:c.567-2A>G, p.?) and subsequently, WES revealed a heterozygous de novo missense allelic variation in PTPN11 (NM_002834:c.1507G>C, p.(Gly503Arg)) classified pathogenic (class 5) and associated with Noonan syndrome 1. Although the SPTB variant was never described before, splicing algo-