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.

Objectives: This study reports long‐term outcomes from the open‐label extension (OLE) period of the Phase I/II COMPOSER trial (NCT03157635) that evaluated crovalimab in patients with paroxysmal nocturnal haemoglobinuria, who were treatment‐naive or switched from eculizumab at enrolment.Methods: COMPOSER consists of four sequential parts followed by the OLE. The primary OLE objective was to assess long‐term crovalimab safety, with a secondary objective to assess crovalimab pharmacokinetics and pharmacodynamics. Exploratory efficacy endpoints included change in lactate dehydrogenase (LDH), transfusion avoidance, haemoglobin stabilisation and breakthrough haemolysis (BTH).Results: A total 43 of 44 patients entered the OLE after completing the primary treatment period. Overall, 14 of 44 (32%) experienced treatment‐related adverse events. Steady state exposure levels of crovalimab and terminal complement inhibition were maintained over the OLE. During the OLE, mean normalised LDH was generally maintained at ≤1.5× upper limit of normal, transfusion avoidance was achieved in 83%–92% of patients and haemoglobin stabilisation was reached in 79%–88% of patients across each 24‐week interval. Five BTH events occurred with none leading to withdrawal.Conclusions: Over a 3‐year median treatment duration, crovalimab was well tolerated and sustained C5 inhibition was achieved. Intravascular haemolysis control, haemoglobin stabilisation and transfusion avoidance were maintained, signifying long‐term crovalimab efficacy.

To the Editor: Hillmen et al. (March 18 issue)¹ report that breakthrough hemolysis occurred in four patients (10%) receiving pegcetacoplan and in nine (23%) receiving eculizumab for the treatment of paroxysmal nocturnal hemoglobinuria (PNH). They mention in the Discussion that breakthrough hemolysis was reported more often in patients who received eculizumab than in those who received pegcetacoplan and conclude that “a small subgroup of patients may require dose adjustments of pegcetacoplan after cessation of eculizumab; this warrants further study.” The primary problem is that this discussion unfolds without breakthrough hemolysis being defined anywhere in the main text.² If we look at . . .