PSTPIP1-Associated Myeloid-Related Proteinemia Inflammatory (PAMI) Syndrome: A Systematic Review

PSTPIP1 (proline-serine-threonine phosphatase-interactive protein 1)-associated myeloid-related proteinemia inflammatory (PAMI) syndrome, previously known as Hyperzincemia/Hypercalprotectinemia (Hz/Hc) syndrome, is a recently described, rare auto-inflammatory disorder caused by specific deleterious variants in the PSTPIP1 gene (p.E250K and p.E257K). The disease is characterized by chronic systemic inflammation, cutaneous and osteoarticular manifestations, hepatosplenomegaly, anemia, and neutropenia. Increased blood levels of MRP 8/14 and zinc distinguish this condition from other PSTPIP1-associated inflammatory diseases (PAID). The aim of this systematic review is to provide a comprehensive overview of the disease phenotype, course, treatment, and outcome based on reported cases. This systematic review adheres to the PRISMA guidelines (2020) for reporting. A literature search was performed in Embase, Medline, and Web of Science on 13 October 2022. The quality of the case reports and case series was assessed using the JBI checklists. Out of the 43 included patients with PAMI syndrome, there were 24 females and 19 males. The median age at onset was 3.9 years. The main clinical manifestations included anemia (100%), neutropenia (98%), cutaneous manifestations (74%), osteoarticular manifestations (72%), splenomegaly (70%), growth failure (57%), fever (51%), hepatomegaly (56%), and lymphadenopathy (39%). Systemic inflammation was described in all patients. Marked elevation of zinc and MRP 8/14 blood levels were observed in all tested patients. Response to treatment varied and no consistently effective therapy was identified. The most common therapeutic options were corticosteroids (N = 30), anakinra (N = 13), cyclosporine A (N = 11), canakinumab (N = 6), and anti-TNF (N = 14). Hematopoietic stem cell transplantation has been recently reported to be successful in five patients. Our review highlights the key characteristics of PAMI syndrome and the importance of considering this disease in the differential diagnosis of patients presenting with early-onset systemic inflammation and cytopenia.

The clinical and biological phenotype of PAMI syndrome differentiates this condition from PAPA (pyogenic arthritis, pyoderma gangrenosum [PG], acne) syndrome and the other PSTPIP1-associated inflammatory diseases (PAID).Patients with PAMI syndrome present with chronic systemic inflammation, clinical features of osteoarticular and/or cutaneous manifestations, lymphoproliferation, anemia, and neutropenia.A hallmark of the disease are the increased serum levels of myeloid-related protein (MRP) 8/14 (S100A8/A9 or calprotectin) and zinc [3].
The pathophysiological mechanisms of PAMI syndrome are not completely elucidated.PSTPIP1 is a regulatory phosphatase protein that modulates T-cell and phagocyte activation, cytoskeletal organization, and IL-1 production [1].Specific PSTPIP1 deleterious variants causing PAMI (p.E250K and p.E257K) are thought to lead to an increased binding to the pyrin inflammasome, resulting in inflammasome activation and interleukin (IL)-1β overproduction [1,3].
Although progress has been made in its clinical and genetic characterization, PAMI syndrome is a challenging disease to diagnose because of its rarity, heterogeneity, and overlap with other autoinflammatory conditions.Moreover, clinical management of the disease remains arduous.Various therapeutic approaches have been explored, including non-steroidal anti-inflammatory drugs (NSAIDs), corticosteroids, conventional disease-modifying anti-rheumatic drugs (cDMARDs), and biological disease-modifying anti-rheumatic drugs (bDMARDs), with no effective standard therapy established to date.
Our review aims to provide a comprehensive overview of the disease phenotype, course, treatment, and outcome based on reported cases, and discusses the current understanding of this poorly recognized disease.

Declaration and Protocol
This systematic review is reported following the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) guidelines 2020 [4].
The review protocol was published in the PROSPERO registry database (CRD42022 376098).

Inclusion and Exclusion Criteria 2.2.1. Inclusion Criteria Types of Studies
We included all types of studies (e.g., case reports, case series, prospective observational studies).Only human research and articles with full text available in the English language were included.

Types of Participants
Patients with any of the following characteristics were included:

•
Confirmed PAMI syndrome in the presence of one of the PAMI-specific PSTPIP1 gene deleterious variants (E250K or E257K).

•
Confirmed Hyperzinceamia and Hypercalprotectineamia syndrome in the presence of one of the PAMI-specific PSTPIP1 gene deleterious variants (E250K or E257K).

•
Clinical features of PAPA syndrome in the presence of one of the PAMI-specific PSTPIP1 gene deleterious variants (E250K or E257K).

•
Clinical features of PAID in the presence of one of the PAMI-specific PSTPIP1 gene deleterious variants (E250K or E257K).

Exclusion Criteria
• Patients with of one of the PAMI-specific PSTPIP1 gene deleterious variants (E250K or E257K), but without any clinical or biological manifestations.

•
Patients reported as carrying the clinical diagnosis PAMI syndrome, but without evidence of PAMI-specific PSTPIP1 gene deleterious variants (E250K or E257K) (i.e., genetic analysis not performed, or alternative deleterious variants identified).
It should be noted that the references by Sampson, Isidor, Fessatou, Sugiura and Demidowich et al. [5][6][7][8][9] were initially excluded, but later included in relation to the genetic results published in the study by Holzinger et al. in 2015 [3].

Search Strategy and Selection Process
A literature search was performed using three Databases (Embase.com,Medline All Ovid and Web of Science Core collection) on 13 October 2022 by a researcher (MM) with the assistance of a medical librarian (CJ).There were no limits regarding the research strategies.The complete search strategies used are shown in Supplementary File S1.
Retrieved records were imported into Endnote 20 (Clarivate Analytics, USA) and duplicates were removed (CJ).Then, MM and KT proceeded to the selection of articles, working independently and in a double-blind way using the Rayyan Web tool [10].The titles and abstracts of all remaining articles were reviewed, and those that were not relevant to the review topic or did not meet the inclusion criteria were excluded.The same two researchers conducted a full reading of the texts and then resolved disagreements through consensus.Finally, the quality of the case reports and case series was assessed by Manel Mejbri using the JBI checklists [11,12].The JBI checklist for the case reports consisted of 8 items with a classification of 'yes', 'no', 'unclear', or 'not applicable'.Items 7 and 8 were not applicable for our review.Only cases with 'yes' items [4][5][6] were included.The JBI checklist for case series consisted of 10 items with a classification of 'yes', 'no', 'unclear', or 'not applicable'.Only cases with 'yes' items [7][8][9][10] were included.A PRISMA flow diagram describing the case selection process is shown in Figure 1 [4].

Data Collection and Data Items
An Excel spreadsheet was used to manage and extract relevant data from the articles included in the review.To test for accuracy, a second researcher reviewed extracted data for at least 50% of the papers.The spreadsheet included details such as publication details

Data Collection and Data Items
An Excel spreadsheet was used to manage and extract relevant data from the articles included in the review.To test for accuracy, a second researcher reviewed extracted data for at least 50% of the papers.The spreadsheet included details such as publication details (year, author, journal), age of onset, sex, family history, general signs, lymphadenopathy/hepatomegaly/splenomegaly, dermatologic signs, osteoarticular signs, hematologic signs, growth failure, other clinical symptoms reported, biologic findings (WBC, ANC, Hb, platelets, CRP, SAA, ESR, plasma zinc, MRP8/14), genetic results, and previous and current treatment (dosage, duration, and adverse events), as well as outcome and evolution, if available.
If the information was not available in the article, it was noted as such.
The demographics and the clinical presentations of the patients are summarized in Table 1.

Demographics
Out of the 43 included patients with PAMI syndrome, 24 were females (56%) and 19 were males (44%), resulting in a male: female ratio of 0.79.Unfortunately, we were unable to determine any clustering of ethnic groups or pattern of consanguinity in these cases, as many articles did not provide this information.
We observed a median age at disease onset to be 3.9 years.In 38% of patients, the first symptoms appeared before their first birthday.In the reported cases, the disease can manifest at any time between birth and 18 years of age; however, over 80% of patients experienced their first symptoms before the age of six years (Figure 2).The age at diagnosis varied widely, ranging from 6 months to 56 years.It is important to highlight that there was often a significant delay from clinical presentation to diagnosis, with a median delay of 9.3 years.

Demographics
Out of the 43 included patients with PAMI syndrome, 24 were females (56%) and 19 were males (44%), resulting in a male: female ratio of 0.79.Unfortunately, we were unable to determine any clustering of ethnic groups or pattern of consanguinity in these cases, as many articles did not provide this information.
We observed a median age at disease onset to be 3.9 years.In 38% of patients, the first symptoms appeared before their first birthday.In the reported cases, the disease can manifest at any time between birth and 18 years of age; however, over 80% of patients experienced their first symptoms before the age of six years (Figure 2).The age at diagnosis varied widely, ranging from 6 months to 56 years.It is important to highlight that there was often a significant delay from clinical presentation to diagnosis, with a median delay of 9.3 years.

Clinical Presentation and Disease Course
Patients with PAMI syndrome presented with early-onset systemic inflammation, along with a variety of inflammatory features ranging from mild symptoms to severe presentations.In our review a predominant pattern emerged, with 88% of cases exhibiting serious manifestations characterized by severe cytopenia and/or prominent cutaneous or

Clinical Presentation and Disease Course
Patients with PAMI syndrome presented with early-onset systemic inflammation, along with a variety of inflammatory features ranging from mild symptoms to severe presentations.In our review a predominant pattern emerged, with 88% of cases exhibiting serious manifestations characterized by severe cytopenia and/or prominent cutaneous or osteoarticular symptoms, and in some cases growth failure and organ involvement.A milder phenotype was observed in 12% of cases, characterized by biologic inflammation with mild cytopenia and/or mild skin or osteoarticular symptoms.
Interestingly, phenotypic heterogeneity was observed among family members sharing the same variants [2,3,19,21,29].In most patients, clinical symptoms appeared gradually over a period of several years.
Furthermore, 16 (37%) out of 43 patients were reported to have experienced recurrent infections, two of which were complicated by septic shock.One of these two patients died at 36 years of age due to multiple organ failure.Macrophage activation syndrome (MAS) was reported in 4 patients (9%).
The main clinical manifestations of PAMI syndrome and their frequency are illustrated in Figures 3 and 4. The main clinical manifestations of PAMI syndrome and their frequency are illustrated in Figures 3 and 4

Laboratory, Histology and Genetic Findings
All patients had hematological involvement, i.e., mild to severe anemia in 100% and neutropenia in 98% of cases, respectively (with ranges of Hb = 20-117 g/L and ANC = 0.08 to 1.3 G/L).Thrombocytopenia was present in 41% of cases, while 9% exhibited thrombocytosis.
Systemic inflammation was evidenced in all reported cases using the monitoring of CRP, ESR or SAA.Markedly elevated concentrations of zinc and MRP8/14 were detected in all tested patients.

Laboratory, Histology and Genetic Findings
All patients had hematological involvement, i.e., mild to severe anemia in 100% and neutropenia in 98% of cases, respectively (with ranges of Hb = 20-117 g/L and ANC = 0.08 to 1.3 G/L).Thrombocytopenia was present in 41% of cases, while 9% exhibited thrombocytosis.
Systemic inflammation was evidenced in all reported cases using the monitoring of CRP, ESR or SAA.Markedly elevated concentrations of zinc and MRP8/14 were detected in all tested patients.
Immunologic investigations revealed the presence of antineutrophil antibodies or laboratory data consistent with autoimmune neutropenia in 53% of the patients studied (8/15).The presence of antinuclear antibodies and rheumatoid factor was reported, respectively, in 13 and 9 patients.Among them, only one patient tested positive for both.This patient also exhibited decreased complement levels (C3, C4) and a positive direct antiglobulin test.
NK cell deficiency was observed in 7 out of 12 studied patients (58%).Additionally, cytokine profiling performed in 15 cases revealed elevated levels of IL-18 in all tested patients (12 out of 12) and high levels of IL-1β in 13 out of 14 cases, with the only case presenting normal IL-1β levels undergoing treatment.Furthermore, an increased expression of type I interferon (IFN)-regulated genes (positive IFN signature) was reported in 3 cases.
Genetic analysis of the PSTPIP1 gene revealed that in a significant majority of cases, 41 out of 43 (95%) exhibited the heterozygous E250K variant.Only two patients in our review had the E257K variant.Among the reviewed cases, 6 out of 26 involved an inheritance from one of their parents, while 20 cases (76%) were carriers of the de novo variants.Unfortunately, information was unavailable for 17 patients.
Genes 2023, 14, x FOR PEER REVIEW 13 of 16 Notably, among the patients who received anti-IL1 therapy, 40% (6/15) showed significant improvement, either when given as monotherapy (4/6), or in combination therapy with cyclosporine (1/6) or tacrolimus and oral steroids (1/6).On the other hand, anti-TNF treatment yielded variable results, with 57% (8/14) of patients showing improvement of osteoarticular and/or cutaneous manifestations and a reduction in biologic inflammation.Half of the patients required a combination treatment; two with steroids, one with methotrexate, and one with methotrexate, cyclosporine and steroids.Tocilizumab was found to be ineffective overall, as only one patient reported an improvement before discontinuing treatment due to lack of persistent efficacy.Cyclosporine A demonstrated partial effectiveness in 9 out of 11 patients, however it was administered in combination with steroids in all cases, with or without another biologic treatment.Interestingly, NSAIDs as monotherapy were found to be effective in addressing systemic inflammation, anemia, and osteoarticular symptoms in three patients.
In 2020, Laberko et al. [20] became the first team to conduct an allogenic hematopoietic stem cell transplantation (HSCT) for five patients with PAMI syndrome.In four of these patients, the indication was lack of PAMI disease control, while the occurrence of myelodysplastic syndrome justified HSCT in the fifth case.HSCT was successful in four cases, while a fifth patient required a second HSCT due to graft rejection.At the last follow-up (median 2.2 years), all five patients were free of PAMI symptoms, with adequate immune recovery.

Discussion
This review describes the phenotype of 43 patients with confirmed PAMI syndrome.PAMI syndrome is characterized by early onset systemic inflammation, cytopenia, lymphoproliferation, cutaneous and/or osteoarticular manifestations.While primarily affecting these areas, our review highlighted that other organs may also be affected considerably.Several authors have reported gastrointestinal involvement, with 16% of cases experiencing flare-ups of colitis and/or chronic diarrhea [3,16,19,20,24,28,29].Notably, 57% of these patients developed the disease within the first few months of life, suggesting that Notably, among the patients who received anti-IL1 therapy, 40% (6/15) showed significant improvement, either when given as monotherapy (4/6), or in combination therapy with cyclosporine (1/6) or tacrolimus and oral steroids (1/6).On the other hand, anti-TNF treatment yielded variable results, with 57% (8/14) of patients showing improvement of osteoarticular and/or cutaneous manifestations and a reduction in biologic inflammation.Half of the patients required a combination treatment; two with steroids, one with methotrexate, and one with methotrexate, cyclosporine and steroids.Tocilizumab was found to be ineffective overall, as only one patient reported an improvement before discontinuing treatment due to lack of persistent efficacy.Cyclosporine A demonstrated partial effectiveness in 9 out of 11 patients, however it was administered in combination with steroids in all cases, with or without another biologic treatment.Interestingly, NSAIDs as monotherapy were found to be effective in addressing systemic inflammation, anemia, and osteoarticular symptoms in three patients.
In 2020, Laberko et al. [20] became the first team to conduct an allogenic hematopoietic stem cell transplantation (HSCT) for five patients with PAMI syndrome.In four of these patients, the indication was lack of PAMI disease control, while the occurrence of myelodysplastic syndrome justified HSCT in the fifth case.HSCT was successful in four cases, while a fifth patient required a second HSCT due to graft rejection.At the last follow-up (median 2.2 years), all five patients were free of PAMI symptoms, with adequate immune recovery.

Discussion
This review describes the phenotype of 43 patients with confirmed PAMI syndrome.PAMI syndrome is characterized by early onset systemic inflammation, cytopenia, lymphoproliferation, cutaneous and/or osteoarticular manifestations.While primarily affecting these areas, our review highlighted that other organs may also be affected considerably.
Several authors have reported gastrointestinal involvement, with 16% of cases experiencing flare-ups of colitis and/or chronic diarrhea [3,16,19,20,24,28,29].Notably, 57% of these patients developed the disease within the first few months of life, suggesting that PAMI syndrome should be considered in the differential diagnosis of early onset inflammatory bowel disease (IBD).Similarly, kidney involvement has been identified in PAMI syndrome, as indicated by Borgia et al. [23].They found that heterogenous nephropathies can be part of the clinical spectrum of the syndrome, underlining the importance of regular renal evaluations.The same authors suggested canakinumab as a possible treatment for these manifestations.Another significant aspect of PAMI syndrome is neurologic impairment, with 11% of cases exhibiting developmental delay.Del Borello et al. recently reported a case showing significant improvement in the neurobehavioral profile and resolution of cerebral atrophy six months after initiating anakinra treatment [22].These findings highlight the broad spectrum of clinical manifestations associated with PAMI syndrome, which can vary from mild cases without skin and/or osteoarticular manifestations to severe cases with a progressive course and organ involvement.Interestingly, even within the same family with an identical variant, the phenotype showed variability, probably due to an incomplete penetrance [29], as also reported in PAPA syndrome.Despite the distinct clinical presentations and the phenotypic variability, our review affirms that cytopenia, systemic inflammation, and elevated levels of zinc and MRP8/14 consistently emerge as the hallmark features observed in all patients.These markers may be used as screening tests for suspected cases in order to facilitate prompt diagnosis and an earlier disease control.
The pathophysiology of hematologic findings in PAMI syndrome remains unclear.Interestingly, neutropenia remained unchanged in all patients under treatment, despite the improvement of anemia and the resolution of systemic inflammation reported in some cases.
Interestingly, among the 43 PAMI cases reported in this review, one presented with a lupus-like phenotype (patient N • 8, Table 1) [17,31], suggesting that including the PSTPIP1 gene in lupus genetic panels might be of interest.Broadening the scope of genetic testing in patients presenting with the PAMI phenotype may lead to the discovery of new PAMIspecific variants in the future.Recently, a novel PSTP1 variant (N236K) has been reported to be associated with the PAMI phenotype, suggesting that E250K and E257K may not be the only PAMI-specific PSTPIP1 gene deleterious variants [32].
No consistently effective therapy has yet been identified for PAMI syndrome.The response to anti-cytokine therapies varies among cases, with some patients demonstrating significant improvement upon initiation of such treatments, while others show no response.Globally, anti-TNF therapy appears to be more effective than anti-IL-1 therapy, with 57% of patients experiencing improvement compared to 40% with anti-IL-1 therapy.These improvements include skin and osteoarticular manifestations, as well as systemic inflammation, lymphoproliferation, and anemia.However, the efficacy of anti-TNF agents was more often observed in a combination treatment with steroids and/or cDMARDs, while anti-IL-1 therapy seems to be more frequently effective as a monotherapy.Notably, anti-IL-1 therapy has shown promising efficacy even for severe manifestations involving the neurologic, gastrointestinal and renal systems [19,22,23].Our review also suggests that there may also be a role for NSAID, corticosteroids, or cyclosporine in the symptomatic treatment of this condition.
HSCT demonstrated successful outcomes in a small number of patients treated to date, leading to the resolution of PAMI symptoms, normalization of inflammatory markers and zinc levels, and discontinuation of specific therapies.This is in line with the prevailing view that the effectiveness of HSCT in autoinflammatory diseases is still uncertain.HSCT could be considered for patients with an incomplete response to conventional therapies, including those requiring G-CSF therapy.However, further research with larger patient numbers and longer follow-up is essential to determine whether HSCT may provide a curative option for a subset of PAMI patients with a severe disease course.

Figure 4 .
Figure 4. Distribution of the clinical manifestations of PAMI syndrome.

Figure 4 .
Figure 4. Distribution of the clinical manifestations of PAMI syndrome.

Figure 5 .
Figure 5. Response to different treatment.

Figure 5 .
Figure 5. Response to different treatment.

Table 1 .
Clinical features of patients with PAMI syndrome.
* Complete description of the patient in the Supplementary File S2.