hemophagocytic lymphohistiocytosis ( hlh ) is a hyperinflammatory disorder with clinical manifestations that include fever , organomegaly , and cytopenia1 ) .
hlh occurs either as a primary form ( genetic or familial ) or as a secondary form ( acquired)2 ) .
the familial form of hlh ( fhl ) is a potentially fatal autosomal recessive disorder due to constitutionally defective cell - mediated cytotoxicity3 ) . in particular , the onset of fhl
is reported to be within one year after birth in 70% to 80% of the cases . until now
, five genetic loci for fhl ( fhl1-fhl5 ) have been reported , involving the following four causative genes : prf1 ( fhl2 ) , unc13d ( fhl3 ) , stx11 ( fhl4 ) , and stxbp2 ( fhl5)3 ) . in this report
, we describe a fatal case of fhl2 due to a novel prf1 gene mutation in a newborn girl with severe clinical manifestations that mimicked severe sepsis .
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 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 .
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 ( fig .
the 7th day of the admission , laboratory finding revealed leukocytes level at 4,01010/l , thrombocytes 2810/l , hemoglobin 9.7 g / dl , absolute neutropenic counts 96010/l , triglyceride 774 mg / dl , ferritin 165,000 ng / ml , fibrinogen 93 mg / dl .
laboratory 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 modifications4 ) .
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 ( fig .
2a ) . 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 described5 ) . 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 ] ( fig .
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 .
in this report , we described a fatal neonatal case of fhl2 due to mutations of prf1 , including a novel frameshift mutation .
the patient 's complicated multiorgan manifestations and fulminant clinical course mimicking severe sepsis delayed the diagnosis of fhl .
the family history included a deceased sister with similar clinical manifestations , which led us to search for a genetic etiology .
since the onset of fhl is typically young , frequently < 1 year6 ) , clinical suspicion for fhl is critical for timely diagnosis and proper management to improve the prognosis of the disease in neonatal intensive care .
flow cytometric analysis of the intracytoplasmic perforin expression of cytotoxic cells and , more recently , intraplatelet expression of munc 13 - 4 protein have been introduced to screen for fhl2 and fhl3 , respectively4,7 ) .
our patient showed a complete deficiency of perforin in both nk cells and cd8 + t cells , while her carrier parents had a partial deficiency in nk cells and a complete deficiency in cd8 + t cells , respectively .
this observation is in line with the findings described in a previous report4 ) . at the molecular level ,
the patient was compound heterozygous for two point mutations , c.65delc ( p.pro22argfs*2 ) and c.1090_1091delct ( p.leu364glufs*93 ) .
both mutations are deleterious in nature by way of introduction of a premature stop codon due to a frameshift .
the complete deficiency of perforin expression revealed by flow cytometric analysis could be interpreted in the context of a genotype - phenotype correlation : two deleterious mutant alleles resulting in severe protein deficiency and the early age of onset followed by a fulminant clinical course .
based on a review of the literature and mutation database ( human gene mutation database professional ; http://www.hgmd.org/ ) , c.65delc is a novel mutation .
the c.1090_1091delct mutation had been reported in a korean patient ( a two - month - old girl ) with homozygous status in our previous study5 ) .
interestingly , c.1090_1091delct was reported to be the most frequent fhl2 mutation in japan8 ) .
the small number of fhl2 in korea is due to the unusual predominance of fhl3 ( ~90%)5 ) .
collectively , c.1090_1091delct is restricted to fhl2 of korean and japanese descendents with high frequencies , suggesting a distinct geographical distribution and founder effect , as exemplified by prf1:c.50delt mutation in fhl2 in people of african ancestry9 ) .
clinically , our patient had a course that rapidly deteriorated into multiorgan failure requiring continuous veno - venous hemodiafiltration .
severe lactic acidosis and a family history of a sibling who had died from similar clinical manifestations that mimicked sepsis led us to suspect bacterial sepsis with a genetic etiology of metabolic disease .
the suspicion of fhl was delayed until we obtained negative results for bacteriologic and metabolic workup . however , persistent fever , sepsis - like features , and a progressively deteriorating clinical course may suggest the diagnosis of fhl in neonates10 ) . in previous data , three cases of fhl in identical male twins and their younger brother who presented with fever and severe
one of them showed reversed cd4/cd8 ratio ( 0.52 ) in flowcytometric lymphocyte subset analysis and aspirate of bone marrow revealed typical features consistent with fhl in two of them . but none of them performed direct sequencing analysis11 ) .
as exemplified by the present case , fhl needs to be considered as one of the differential diagnoses when a newborn presents with severe sepsis - like features with progressive multiorgan failure . in summary
, we described a fatal neonatal case of fhl2 that mimicked severe sepsis . clinical assessment and laboratory workup for fhl
is needed in critically ill neonates with severe sepsis and multiorgan failure , particularly when there is no evidence of a microbiological or metabolic cause .
 hemophagocytic lymphohistiocytosis ( hlh ) occurs in the primary form ( genetic or familial ) or secondary form ( acquired ) . 
 the familial form of hlh ( fhl ) is a potentially fatal autosomal recessive disorder that occurs because of constitutional defects in cell - mediated cytotoxicity . here , we report a fatal neonatal case of type 2 fhl ( fhl2 ) that involved a novel frameshift mutation . 
 clinically , the newborn presented with severe sepsis - like features and required mechanical ventilation and continuous venovenous hemodiafiltration . 
 flow cytometry analysis showed marked hlh and complete absence of intracytoplasmic perforin expression in cytotoxic cells ; therefore , we performed molecular genetic analyses for prf1 mutations , which showed that the patient had a compound heterozygous mutation in prf1 , that is , c.65delc ( p.pro22argfs*2 ) and c.1090_1091delct ( p.leu364glufs*93 ) . 
 clinical and genetic assessments for fhl are required for neonates with refractory fever and progressive multiple organ failure , particularly when there is no evidence of microbiological or metabolic cause . 
Introduction
Case report
Discussion