docling/tests/data/groundtruth/docling_v2/1349-7235-63-2651.nxml.md

Atypical Hemolytic Uremic Syndrome Triggered by Acute Pancreatitis in a Patient with a Membrane Cofactor Protein (CD46) Genetic Variant

Kosuke Mochizuki; Department of Nephrology, Kansai Electric Power Hospital, Japan; Naohiro Toda; Department of Nephrology, Kansai Electric Power Hospital, Japan; Masaaki Fujita; Department of Rheumatology, Kansai Electric Power Hospital, Japan; Satoshi Kurahashi; Department of Nephrology, Kansai Electric Power Hospital, Japan; Hisako Hirashima; Department of Nephrology, Kansai Electric Power Hospital, Japan; Kazuki Yoshioka; Department of Hematology, Kansai Electric Power Hospital, Japan; Tomoya Kitagawa; Department of Hematology, Kansai Electric Power Hospital, Japan; Akira Ishii; Department of Nephrology, Kansai Electric Power Hospital, Japan; Toshiyuki Komiya; Department of Nephrology, Kansai Electric Power Hospital, Japan

Atypical hemolytic uremic syndrome (aHUS) is a type of HUS. We herein report a case of aHUS triggered by pancreatitis in a patient with a heterozygous variant of membrane cofactor protein ( MCP ; P165S), a complement-related gene. Plasma exchange therapy and hemodialysis improved thrombocytopenia and anemia without leading to end-stage kidney disease. This MCP heterozygous variant was insufficient to cause aHUS on its own. Pancreatitis, in addition to a genetic background with a MCP heterozygous variant, led to the manifestation of aHUS. This case supports the “multiple hit theory” that several factors are required for the manifestation of aHUS.

Introduction

In the Kidney Disease: Improving Global Outcomes (KDIGO) classification, TMA is classified into four categories: STEC-HUS induced by Shiga toxin-producing Escherichia coli (STEC) infection, thrombotic thrombocytopenic purpura (TTP), “primary aHUS,” and “secondary aHUS.” TTP is caused by a marked deficiency in a disintegrin-like and metalloproteinase with thrombospondin type 1 motifs 13 (ADAMTS-13) activity, either because of genetic abnormalities or acquired autoantibodies. Conversely, more than 90% of HUS cases are STEC-HUS, and the remaining 10% are aHUS, which does not involve STEC infection (1,2). The term “primary aHUS” is used when an underlying abnormality of the alternative pathway of complement is strongly suspected, and other causes of “secondary aHUS” have been excluded.

Pathogenic genetic variants in a patient with aHUS include complement factor H (CFH), membrane cofactor protein (MCP; CD46), complement factor I (CFI), complement 3 (C3), complement factor B (CFB), thrombomodulin (THBD), complement factor H related protein 1 (CFHR1), complement factor H related protein 5 (CFHR5), and diacylglycerol kinase epsilon (DGKE) (3-6). Fujisawa et al. reported that, in an analysis of 118 aHUS patients in Japan, the frequencies of C3, CFH, MCP and DGKE genetic abnormalities were 32 (27%), 10 (8%), 5 (4%), and 1 (0.8%), respectively, and the frequency of anti-CFH antibodies was 20 (17%). Unidentified genetic abnormalities were reported in 36 patients (30%) (7). However, even in some patients, a complement abnormality could not be identified.

Case Report

The laboratory data are shown in Table 1. After EUS-FNA, the patient complained of left-sided abdominal pain, and the pancreatic amylase level was found to have increased to 1,547 U/L. The patient's vital signs were as follows: body temperature, 37.5°C; and blood pressure, 136/74 mmHg. Contrast-enhanced computed tomography (CT) revealed a contrast-impaired area of the pancreatic tail and increased peripancreatic fatty tissue density (Figure A). The patient was diagnosed with acute pancreatitis after EUS-FNA. Treatment was started with fasting, analgesia with acetaminophen, treatment with nafamostat-mesylate, and large extracellular fluid replacement of 4,000 mL/day. Serum creatinine increased from 0.75 to 1.33 mg/dL, and the estimated glomerular filtration rate (eGFR) decreased from 87 to 46.5, indicating acute kidney injury. The urinary protein excretion was 6.15 g/gCr, and hematuria (3+) was observed. Blood samples showed progression of anemia from Hb 15.5 to 12.4 mg/dL, and platelets decreased from 313,000 to 5,000/μL. Schistocytes were detected at a rate of 50-70/2,000 red blood cells (RBCs), lactate dehydrogenase (LDH) levels were elevated to 2,469 U/L, and haptoglobin was 23 mg/dL.

The patient was found to have suffered a relapse of inflammation and showed elevated pancreatic enzymes on day X+7. CT showed pancreatic swelling and hypo-absorptive areas in the peripancreatic, gastric fold, and transverse colonic mesentery, suggesting the formation of walled-off necrosis (WON) (Figure B). The WON improved with antibiotic treatment. After confirming no recurrence of postprandial abdominal pain, the patient was discharged on day X+26.

We outsourced next-generation sequencing of complement-related genetic abnormalities to the KAZUSA DNA Research Institute. In the laboratory, CFH, CFI, MCP, C3, CFB, THBD, DGKE, and CFHR5 were analyzed using next-generation sequencing hybridization capture methods for rare single nucleotide substitutions and deletions with an allele frequency of <0.5%. In addition, complement function tests (sheep erythrocyte hemolysis test) and anti-CFH antibody tests were performed. The sheep erythrocyte hemolysis test was performed because it is useful for detecting genetic mutations in CFH and anti-CFH antibodies. The results showed the absence of anti-CFH antibodies (8). Genetic testing revealed a 493-base cytosine (C) to thymine (T) mutation in MCP (MCP P165S), a complement-related gene responsible for atypical HUS, resulting in a missense variant of proline-to-serine substitution and a heterozygous mutation in MCP. Based on the MCP findings, we considered this case to potentially be primary aHUS triggered by acute pancreatitis.

Discussion

In the present case, the patient had a missense variant of MCP (MCP P165S). A previous report indicated a 50% reduction in MCP expression in leukocytes in patients with the MCP P165S variant (9). Another study reported that a 50% reduction in MCP expression leads to a decrease in the binding ability of C3b to <50% compared to normal MCP expression (10). The MCP P165S variant is not registered in Clinvar but is categorized as “likely pathogenic” according to the The American College of Medical Genetics and Genomics guidelines (ACMG guidelines) (11). Esparaza-Gordillio et al. reported families with the same genetic variant as this case and found that patients with only the MCP variant did not manifest aHUS, whereas those with coexisting the CFI mutation and MCPggaac single-nucleotide variant haplotype block, another variant of MCP, did manifest aHUS (9,12,13). The clinical characteristics of the patients with the MCP P165S variant are summarized in Table 2. In the present case, only the protein-coding region exons of CFH, CFI, CD46, C3, CFB, THBD, and DGKE and their intron boundaries were searched using the next-generation sequencer, and the multiple ligation-dependent probe amplification (MLPA) method was not used to detect structural variants. The lack of a genetic analysis using MLPA is considered a limitation of this case (14).

Several triggers are thought to be involved in the manifestation of aHUS, in addition to genetic mutations, including infection, pregnancy, transplantation, metabolic diseases, vasculitis, and pancreatitis, called the “multiple hit hypothesis” (13,15-17). Among the reported triggers, cases of aHUS triggered by pancreatitis are rare, accounting for just 3% (4/110) of secondary aHUS cases (18-21). Previously reported cases of aHUS triggered by pancreatitis were not specifically investigated for complement-related gene mutations, so whether or not complement-related gene mutations other than pancreatitis have any effects on the manifestation of aHUS is unclear.

In the present case, aHUS developed in a patient with a genetic variant (MCP P165S) that originally did not meet the threshold for aHUS development due to pancreatitis after EUS-FNA. This shows that several triggers, not just genetic mutations, are involved in the development of aHUS, supporting the “multiple hit hypothesis.” Patients with MCP variants have a better prognosis and lower probability of developing end-stage kidney disease (ESKD) and death than patients with other genetic mutations, such as CFH, CFI, C3, and THBD (13,17,22).

The patient in this case responded well to plasma exchange therapy and PE. He recovered his kidney function, supporting the relatively good prognosis of patients with MCP mutations compared to other aHUS-related gene mutations. Although the efficacy of eculizumab as a treatment for aHUS has been described in recent years, eculizumab was not used in this case, as the patient had a good clinical course with plasma exchange therapy and HD (17,19,21). In addition, infection with WON after pancreatitis was suspected on day X+7; therefore, it was difficult to use eculizumab, which produces immunosuppressive effects. However, the use of eculizumab should be considered in the future if aHUS relapse is triggered by some event.

Tables

Table 1. Progress of Lab-date in This Case.

Variable		DAY0		DAY2		DAY3		DAY4		DAY7		DAY11		DAY14
WBC (×103/μL)		54		112		105		107		210		171		77
Haemoglobin (g/dL)		15.5		12.4		10.5		8.8		7.2		7.9		8.3
Platelets (×104/μL)		31.3		0.5		2.1		1.6		19.6		63.8		83
Cr (mg/dL)		0.75		1.33		1.51		1.67		1.34		1		0.98
LDH (U/L)		151		2,469		2,513		2,024		550		447		362
T-Bil (mg/dL)		0.77		4.35		4.57		4.49		1.98		1		0.82
P-Amy (U/L)		34		1,632		1,080		302		196		134		173
CRP (mg/dL)		0.47		16.76		25.95		15.21		21.22		5.52		1.43
Haptoglobin (mg/dL)		23						<10						88

Table 2. Profiles of the Patients with MCP P165S Variant.

patient	MCP mutation	Other gene variant	sex	Age at onset (yr)	Triggers	onset of aHUS	outcome at first episode	reference
This case	P165S		M	49	pancreatitis	+	Remission
HUS68	P165S	CFI(T538X) MCP ggaac	F	57	n.a.	+	Remission	(9)
HUS84	P165S	CFI(T538X) MCP ggaac	F	41	No trigger	+	Remission	(9)
III-10	P165S		M	52		-		(9)
III-11	P165S	CFI(T538X)	M	54		-		(9)
IV-1	P165S	CFI(T538X)	F	37		-		(9)
IV-2	P165S	CFI(T538X)	M	35		-		(9)
IV-3	P165S		F	30		-		(9)

Figures

Figure. Abdominal computed tomography (CT) findings in this patient. (A) Day X+2 after performing endoscopic ultrasound-guided fine needle aspiration (EUS-FNA). The pancreatic body tail has a mildly reduced contrast effect in the arterial phase, consistent with the findings of acute pancreatitis. (B) Day X+7. CT indicates a low-absorption area suspected of being walled-off necrosis (WON) around the peripancreatic to the gastric body and gastric antrum.

References

• TH Goodship; HT Cook; F Fakhouri; . Atypical hemolytic uremic syndrome and C3 glomerulopathy: conclusions from a “kidney disease: improving global outcomes” (KDIGO) Controversies Conference.. Kidney Int (2017)
• M Noris; G Remuzzi. Atypical hemolytic-uremic syndrome.. N Engl J Med (2009)
• J Caprioli; M Noris; S Brioschi; . Genetics of HUS: the impact of MCP, CFH, and IF mutations on clinical presentation, response to treatment, and outcome.. Blood (2006)
• CJ Fang; V Fremeaux-Bacchi; MK Liszewski; . Membrane cofactor protein mutations in atypical hemolytic uremic syndrome (aHUS), fatal Stx-HUS, C3 glomerulonephritis, and the HELLP syndrome.. Blood (2008)
• V Fremeaux-Bacchi; EA Moulton; D Kavanagh; . Genetic and functional analyses of membrane cofactor protein (CD46) mutations in atypical hemolytic uremic syndrome.. J Am Soc Nephrol (2006)
• V Fremeaux-Bacchi; MA Dragon-Durey; J Blouin; . Complement factor I: a susceptibility gene for atypical haemolytic uraemic syndrome.. J Med Genet (2004)
• M Fujisawa; H Kato; Y Yoshida; . Clinical characteristics and genetic backgrounds of Japanese patients with atypical hemolytic uremic syndrome.. Clin Exp Nephrol (2018)
• Y Yoshida; T Miyata; M Matsumoto; . A novel quantitative hemolytic assay coupled with restriction fragment length polymorphisms analysis enabled early diagnosis of atypical hemolytic uremic syndrome and identified unique predisposing mutations in Japan.. PLoS One (2015)
• J Esparza-Gordillo; EG Jorge; CA Garrido; . Insights into hemolytic uremic syndrome: segregation of three independent predisposition factors in a large, multiple affected pedigree.. Mol Immunol (2006)
• A Richards; EJ Kemp; MK Liszewski; . Mutations in human complement regulator, membrane cofactor protein (CD46), predispose to development of familial hemolytic uremic syndrome.. Proc Natl Acad Sci U S A (2003)
• S Richards; N Aziz; S Bale; . Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology.. Genet Med (2015)
• J Esparza-Gordillo; E Goicoechea de Jorge; A Buil; . Predisposition to atypical hemolytic uremic syndrome involves the concurrence of different susceptibility alleles in the regulators of complement activation gene cluster in 1q32.. Hum Mol Genet (2005)
• E Bresin; E Rurali; J Caprioli; . Combined complement gene mutations in atypical hemolytic uremic syndrome influence clinical phenotype.. J Am Soc Nephrol (2013)
• Y Sugawara; H Kato; M Nagasaki; . CFH-CFHR1 hybrid genes in two cases of atypical hemolytic uremic syndrome.. J Hum Genet (2023)
• M Riedl; F Fakhouri; Quintrec M Le; . Spectrum of complement-mediated thrombotic microangiopathies: pathogenetic insights identifying novel treatment approaches.. Semin Thromb Hemost (2014)
• F Fakhouri; L Roumenina; F Provot; . Pregnancy-associated hemolytic uremic syndrome revisited in the era of complement gene mutations.. J Am Soc Nephrol (2010)
• JM Campistol; M Arias; G Ariceta; . An update for atypical haemolytic uraemic syndrome: diagnosis and treatment. A consensus document.. Nefrologia (2015)
• Clech A Le; N Simon-Tillaux; F Provôt; . Atypical and secondary hemolytic uremic syndromes have a distinct presentation and no common genetic risk factors.. Kidney Int (2019)
• J Barish; P Kopparthy; B Fletcher. Atypical haemolytic uremic syndrome secondary to acute pancreatitis: a unique presentation.. BMJ Case Rep (2019)
• T Kajiyama; M Fukuda; Y Rikitake; O Takasu. Atypical hemolytic uremic syndrome secondary to pancreatitis: a case report.. Cureus (2023)
• O Taton; M Delhaye; P Stordeur; T Goodship; Moine A Le; A Massart. An unusual case of haemolytic uraemic syndrome following endoscopic retrograde cholangiopancreatography rapidly improved with eculizumab.. Acta Gastroenterol Belg (2016)
• M Noris; J Caprioli; E Bresin; . Relative role of genetic complement abnormalities in sporadic and familial aHUS and their impact on clinical phenotype.. Clin J Am Soc Nephrol (2010)