Stepensky P, Keller B, Abuzaitoun O, Shaag A, Yaacov B, Unger S, Seidl M, Rizzi M, Weintraub M, Elpeleg O, Warnatz K. Extending the clinical and immunological phenotype of human interleukin-21 receptor deficiency. Haematologica 2015; 100(2):e72-e76; https://doi.org/10.3324/haematol.2014.112508.