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To the Editor:

Pyoderma gangrenosum (PG) is a skin disorder affecting approximately 2%–5% of patients with inflammatory bowel disease (IBD). PG can also be part of PAPA syndrome (pyogenic arthritis, pyoderma gangrenosum, and acne),1, 2 which is an autosomal dominant disease caused by mutations A230T and E250Q in the threonine phosphatase-interacting protein 1 (PSTPIP1; CD2BP1) gene on chromosome 15.3 The PSTPIP1 mutations lead to elevated levels of interleukin-1β and have been successfully treated with the recombinant human interleukin-1 receptor antagonist, anakinra.1 Recently a microsatellite variation in the promoter region of PSTPIP1 has been also associated with Crohn's disease (CD) and aseptic abscesses.4 We investigated the case of a 42-year-old male diagnosed with ulcerative colitis at the age of 31 who underwent ileal pouch anal anastomosis for medical failure (including failing cyclosporine and infliximab) with the postoperative complication of severe peristomal PG that resolved with stoma closure but then recrudesced 3 years later when he was again given a stoma for proximal small bowel to pouch fistulizing disease. His diagnosis was changed to CD but his severe, near circumferential peristomal PG was nonresponsive to steroid and infliximab treatment. We speculated that this patient may harbor a PSTPIP1 mutation and therefore be responsive to anakinra treatment.

Peripheral blood B cells and Epstein–Barr virus (EBV)-transformed B cell lines were prepared from blood samples from pyoderma and IBD patients and non-IBD controls. Intestinal tissues of IBD patients were obtained at the time of surgery, and intestinal tissues of non-IBD individuals acquired from NDRI (National Disease Resource Interchange, Philadelphia, PA). Genomic DNA and total RNA were isolated with Qiagen (Chatsworth, CA) kits. We genotyped the two known PAPA syndrome-associated mutations of the PSTPIP1 gene, A230T and E250Q, using a polymerase chain reaction (PCR)-based restriction fragment length polymorphism (RFLP method). No mutation was found for either single nucleotide polymorphism (SNP) in the study case, nor in seven additional IBD patients with pyoderma. To confirm the genotyping result and search for any other mutations in the gene, we directly sequenced a 1363 bp of PCR fragment including the entire amino acid coding sequences, 44 nt of 5′ untranslated region (UTR) and 50 nt of 3′ UTR. No mutation was detected from the sequenced regions. Recently, Andre et al4 detected three microsatellite variants (CCTG)4, (CCTG)5, and (CCTG)7 at nt −405 upstream of the translational start codon ATG. The longest form (CCTG)7 was associated with aseptic abscesses syndrome (AA). AA is a relapsing inflammatory condition that is associated with IBD in 66% of cases (mainly CD in 57%), and also with neutrophilic dermatosis (ND) in 20%.4, 5 Similar to a previous study,4 the study case was affected with PG and also IBD. We directly sequenced 370 bp of a PCR fragment containing the microsatellite repeats, and found that the study case was homozygous for (CCTG)5 allele, i.e., did not have the allele shown to be associated with AA.4

Summarizing the results described above, we conclude that the study case did not carry any known mutation in the entire cDNA nor the promoter region of the PSTPIP1 gene. Accordingly, the patient was found to be nonresponsive to anakinra treatment when given a dose of 100 mg/day for over 8 weeks.

However, we hypothesized that the gene PSTPIP1 may play a role in pyoderma pathogenesis through mechanisms other than genetic mutation. We therefore further examined the gene expression using EBV-transformed B-cell lines generated from the study case and other IBD patients blood samples. We consistently observed a higher level of PSTPIP1 transcripts in the study case and other IBD patients compared to non-IBD family members and unrelated healthy controls. The observed difference was not due to the EBV transformation based on the comparison of EBV-transformed B-cell lines with peripheral blood B cells from the same individuals (Fig. 1A). From reverse-transcription polymerase chain reaction (RT-PCR) analysis of PSTPIP1 transcription, we detected two additional PCR products indicated as B and C in Figure 1A. The result of direct sequencing of these PCR products showed that fragment B had 254 nt of the AHCYL1 (adenosylhomocysteinase-like 1) cDNA sequence from amino acid #333 (exon 10) to #418 (exon 13); and the fragment C had 225 nt of the 3′ UTR (nt #4015 to #4230) of the SMG5 (Smg-5 homolog, nonsense mediated mRNA decay factor) cDNA sequence. Both SMG5 and AHCYL1 are located on human chromosome 1, while PSTPIP1 is located on chromosome 15. Recently, a chromosome t(1;15)(p22;q22) translocation has been shown to be a loss of chromosome material proximal to the breakpoint on chromosome 15 contains the PSTPIP1 gene. The breakpoint is on 1p22, while gene AHCYL1 is located on 1p13.3 and SMG5 1q22.6

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Figure 1. Gene expression of the genes PSTPIP1, SMG5, and AHCYL1 in patients affected with pyoderma and IBD. (A) Gene expression of PSTPIP1 gene in B cells. Left: Comparison of PSTPIP1 expression between peripheral blood B cells and EBV-transformed B-cell lines. Right: Gene expression of PSTPIP1 in EBV-transformed B-cell lines from pyoderma and IBD patients. PCR primers: PST1s and PST13r. (B) Coamplification of PSTPIP1 with SMG5 by RT-PCR with a primer pair of a PSTPIP1 (PST13r, reverse) and SMG5 (SMG7s, forward) from B cells of pyoderma and IBD patients. (C) Gene expression of SMG5 and AHCYL1 in B cells from pyoderma and IBD patients. PCR primers were SMG6s and SMG9r for SMG5, and AHC2s and AHC4r for AHCYL1. (D) Gene expression of SMG5 and AHCYL1 in intestinal tissues from IBD patients. PCR primers were SMG6s and SMG9r for SMG5, and AHC2s and AHC4r for AHCYL1. Sample labels: M: 100 bp DNA markers; H2O: no DNA control; EBV: EBV B cell lines; PB: peripheral blood B cells; Non-dis and Dis: nondiseased and diseased tissue from patients; N: patient's family members without IBD; H: healthy individuals; SI: small intestine; P: pyoderma; C: Crohn's disease; U: ulcerative colitis; *study case.

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The coamplification of PSTPIP1 with SMG5 was further examined by PCR with a primer pair of PSTPIP1 (forward) and SMG5 (reverse). As shown in Figure 1B, a strong PCR amplification was noted in the study case as well as another UC patient (888-57), but no or very weak PCR products from two other CD patients, two non-IBD siblings, and two unrelated healthy controls. The gene expression of AHCYL1 and SMG5 in B cells is shown in Figure 1C. The study case and other UC patients showed a remarkably strong expression of both genes. We also observed strong gene expression of SMG5 and AHCYL1 in intestinal tissues from IBD patients compared to non-IBD individuals, although intestinal tissues from pyoderma patients were not analyzed.

SMG5 plays a role in nonsense-mediated mRNA decay.7AHCYL1 catalyzes the reaction of S-adenosyl-L-homocysteine to adenosine and L-homocysteine.8 A potential role for SMG5 and AHCYL1 in pyoderma, IBD, AA, ND, or any human disease has not been previously reported. The present observation on SMG5 and AHCYL1 is intriguing. Whether the high expression of SMG5 and AHCYL1 has relevance to PSTPIP1, and thus to pyoderma or IBD, is at this time unclear.

REFERENCES

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    Brenner M, Ruzicka T, Plewig G, et al. Targeted treatment of pyoderma gangrenosum in PAPA (pyogenic arthritis, pyoderma gangrenosum and acne) syndrome with the recombinant human interleukin-1 receptor antagonist anakinra. Br J Dermatol. 2009; 161: 11991201.
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    Lindor NM, Arsenault TM, Solomon H, et al. A new autosomal dominant disorder of pyogenic sterile arthritis, pyoderma gangrenosum, and acne: PAPA syndrome. Mayo Clin Proc. 1997; 72: 611615.
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    André MF, Aumaître O, Grateau G, et al. Longest form of CCTG microsatellite repeat in the promoter of the CD2BP1/PSTPIP1 gene is associated with aseptic abscesses and with Crohn disease in French patients. Dig Dis Sci. 2010; 55: 16811688.
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Zhenwu Lin PhD*, John P. Hegarty PhD*, Tony Lin BSII*, Barbara Ostrov MD†, Yunhua Wang BS*, Wei Yu MD, PhD*, Ashley A. Kelly BA*, Lisa S. Poritz MD*, Walter A. Koltun MD*, * Department of Surgery, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, † Department of Pediatrics and Medicine The Pennsylvania State University College of Medicine Hershey, Pennsylvania.