A novel PRF1 gene mutation in a fatal neonate case with type 2 familial hemophagocytic lymphohistiocytosis
The proband was a 29-day-old female infant who was admitted to our institution because of four days of mild fever and rapid breathing, moaning, and mottling. She was the second child of a nonconsanguineous couple, born at 38+4 weeks of gestation with a birth weight of 3,500 g. Family history revealed that her sister died at 28 days of age from sepsis with rapidly progressive clinical manifestations of acute hepatitis, gastrointestinal bleeding, and pulmonary hemorrhage. The initial neonatal course of the proband was not remarkable until she developed respiratory distress and uncontrolled fever on postnatal day 29. She subsequently experienced significant bleeding and bruising from coagulopathy and had hepatosplenomegaly. Her condition deteriorated, and she developed lactic acidosis, 22.38 mmol/L (normal range, 0.5-2.2 mmol/L), which required mechanical ventilation and continuous veno-venous hemodiafiltration ().\nLeukopenia and anemia slowly developed along with thrombocytopenia. The 7th day of the admission, laboratory finding revealed leukocytes level at 4,010×103/µL, thrombocytes 28×103/µL, hemoglobin 9.7 g/dL, absolute neutropenic counts 960×103/µL, triglyceride 774 mg/dL, ferritin 165,000 ng/mL, fibrinogen 93 mg/dL.\nLaboratory workup for infection revealed no diagnostic findings; however, on day 31, broad-spectrum antibiotics and intravenous immunoglobulin and corticosteroid were administered empirically with a presumptive diagnosis of neonatal sepsis. Since the patient's manifestations met the criteria for HLH 2004, a bone marrow study was performed on day 35, which revealed frequent active hemophagocytic histiocytes. As the first step of a diagnostic workup for FHL, we performed flow cytometric analysis for the intracytoplasmic perforin expression of cytotoxic cells using the proband's peripheral blood sample, as previously described with some modifications. We observed a complete absence of perforin expression in the proband's natural killer (NK) cells and CD8+ T cells. The experiments using her parents' blood samples demonstrated partial deficiency of cytoplasmic perforin in NK cells and complete deficiency in CD8+ T cells (). Based on the results of flow cytometric analysis, we obtained written informed consent from the parents and proceeded with a molecular genetic test for FHL2 by direct sequencing analysis of the PRF1 gene, as previously described). As a result, the proband was shown to have two deleterious point mutations of PRF1, c.65delC [p.Pro22Argfs*2] and c.1090_1091delCT [p.Leu364Glufs*93] (. And no other mutation has been found in direct sequencing analysis of the PRF1 gene. Her parents were heterozygous carriers of the respective mutant alleles (compound heterozygous for the c.65delC mutation (of maternal origin; novel) and the c.1090_1091delCT mutation (of paternal origin; known), confirming the compound heterozygous status of the two mutations in the proband. Based on the diagnosis of FHL2, the patient received HLH-2004 chemotherapy with cyclosporine, etoposide, and dexamethasone. She experienced hypotensive episodes that were initially responsive to fluid resuscitation and medications but that eventually progressed to refractory status, leading to renal failure. She died from multiorgan failure on day 43.