Patients with paroxysmal nocturnal hemoglobinuria (PNH) have a clonal population of blood cells deficient in glycosylphosphatidylinositol (GPI)-anchored proteins, resulting from a mutation in the X-linked gene PIGA. Here we report on a set of patients in whom PNH results instead from biallelic mutation of PIGT on chromosome 20. These PIGT-PNH patients have clinically typical PNH, but they have in addition prominent auto-inflammatory features, including recurrent attacks of aseptic meningitis. In all these patients we find a germ-line point mutation in one PIGT allele, whereas the other PIGT allele is removed by somatic deletion of a 20q region comprising maternally imprinted genes implicated in myeloproliferative syndromes. Unlike in PIGA-PNH cells, GPI is synthesized in PIGT-PNH cells and, since its attachment to proteins is blocked, free GPI is expressed on the cell surface. From studies of patients’ leukocytes and of PIGT-knockout THP-1 cells we show that, through increased IL-1β secretion, activation of the lectin pathway of complement and generation of C5b-9 complexes, free GPI is the agent of auto-inflammation. Eculizumab treatment abrogates not only intravascular hemolysis, but also auto-inflammation. Thus, PIGT-PNH differs from PIGA-PNH both in the mechanism of clonal expansion and in clinical manifestations.
Britta Höchsmann, Yoshiko Murakami, Makiko Osato, Alexej Knaus, Michi Kawamoto, Norimitsu Inoue, Tetsuya Hirata, Shogo Murata, Markus Anliker, Thomas Eggermann, Marten Jäger, Ricarda Floettmann, Alexander Höellein, Sho Murase, Yasutaka Ueda, Jun-ichi Nishimura, Yuzuru Kanakura, Nobuo Kohara, Hubert Schrezenmeier, Peter M. Krawitz, Taroh Kinoshita