Identification of mutations in the prostaglandin transporter gene SLCO2A1 and phenotypic comparison between two subtypes of primary hypertrophic osteoarthropathy (PHO): A single-center study

Pathogenesis of chronic enteropathy associated with the SLCO2A1 gene: Hypotheses and conundrums

Chronic enteropathy associated with the SLCO2A1 gene (CEAS) is a complex gastroenterological condition characterized by multiple ulcers in the small intestine with chronic bleeding and protein loss. This review explores the potential mechanisms underlying the pathogenesis of CEAS, focusing on the role of SLCO2A1-encoded prostaglandin transporter OATP2A1 and its impact on prostaglandin E2 (PGE2) levels. Studies have suggested that elevated PGE2 levels contribute to mucosal damage, inflammation, and disruption of the intestinal barrier. The effects of PGE2 on macrophage activation and Maxi-Cl channel functionality, as well as its interaction with nonsteroidal anti-inflammatory drugs play crucial roles in the progression of CEAS. Understanding the balance between its protective and pro-inflammatory effects and the complex interactions within the gastrointestinal tract can shed light on potential therapeutic targets for CEAS and guide the development of novel, targeted therapies.

Comparison of bone microstructure and strength in the distal radius and tibia between the different types of primary hypertrophic osteoarthropathy: an HR-pQCT study

Primary hypertrophic osteoarthropathy (PHO) is a hereditary bone disease that is grouped into PHO autosomal recessive 1 (PHOAR1) and PHO autosomal recessive 2 (PHOAR2) due to different causative genes. Data comparing bone microstructure between the two subtypes are scarce. This is the first study to find that PHOAR1 patients had inferior bone microstructure compared with PHOAR2 patients.

PURPOSE

The primary goal of this study was to assess bone microarchitecture and strength in PHOAR1 and PHOAR2 patients and to compare them with age- and sex-matched healthy controls (HCs). The secondary goal was to assess the differences between PHOAR1 and PHOAR2 patients.

METHODS

Twenty-seven male Chinese PHO patients (PHOAR1 = 7; PHOAR2 = 20) were recruited from Peking Union Medical College Hospital. The areal bone mineral density (aBMD) was assessed by dual-energy X-ray absorptiometry (DXA). Peripheral bone microarchitecture at the distal radius and tibia were evaluated by high-resolution peripheral quantitative computed tomography (HR-pQCT). Biochemical markers of PGE2, bone turnover, and Dickkopf-1 (DKK1) were investigated.

RESULTS

Compared with HCs, PHOAR1 and PHOAR2 patients had distinctively larger bone geometry, substantially lower vBMD at the radius and tibia, and compromised cortical microstructure at the radius. For trabecular bone, PHOAR1 and PHOAR2 patients showed different changes at the tibia. PHOAR1 patients had significant deficits in the trabecular compartment, resulting in lower estimated bone strength. Conversely, PHOAR2 patients showed a higher trabecular number, narrower trabecular separation, and lower trabecular network inhomogeneity than HCs, translating into preserved or slightly high estimated bone strength.

CONCLUSION

PHOAR1 patients had inferior bone microstructure and strength compared with PHOAR2 patients and HCs. Additionally, this study was the first to find differences in the bone microstructure between PHOAR1 and PHOAR2 patients.

A patient with pachydermoperiostosis harboring SLCO2A1 variants with a history of differentiating from acromegaly

Pachydermoperiostosis (PDP) is a rare hereditary disease characterized by digital clubbing, pachydermia, and periostosis. We describe a Japanese male patient with PDP who was differentially diagnosed with acromegaly by identification of compound heterozygous variants in SLCO2A1. Recent studies have reported various clinical manifestations, as well as skeletal and dermal features, in patients with PDP. Genetic testing provided not only PDP diagnosis and differentiation from acromegaly, but also information about possible complications and comorbidities throughout life.

Novel pathogenic variants in SLCO2A1 causing autosomal dominant primary hypertrophic osteoarthropathy

Primary hypertrophic osteoarthropathy (PHO), or pachydermoperiostosis, is characterized by a clinical association including digital clubbing, periostosis and pachydermia. SLCO2A1 and HPGD genes are both responsible for PHO. The pathology is classically defined as an autosomal recessive disorder with clinical variability ranging from a mild to more severe phenotype. However, the hypothesis for an autosomal dominant form suggested for a long time was only demonstrated for the first time in 2021 for SLCO2A1. We aimed to detect a second pathogenic variant by a deep sequencing of the entire SLCO2A1 and HPGD genes, associated with functional transcription analysis in PHO patients harboring only one heterozygous variant. Among 10 PHO patients, 4 presented a single pathogenic or probably pathogenic novel variant in SLCO2A1 in heterozygous status (NM_005630.3: c.234+1G > A, c.1523_1524delCT, c.1625G > A and c.31delC), and the others carried homozygous pathogenic variants. For heterozygous forms, we found no additional pathogenic variant in HPGD or SLCO2A1. PHO can be a dominant form with age at disease onset later than that for the recessive form. This dominant form is not exceptional in young adults. In conclusion, both modes of inheritance of PHO explain the clinical variability and the difference in age at disease onset. Molecular analysis is especially required in the incomplete form to distinguish it from secondary hypertrophic osteoarthropathy.

Crohn-like disease affecting small bowel due to monogenic SLCO2A1 mutations: First cases of Chronic Enteropathy Associated with SLCO2A1 gene (CEAS) in France

INTRODUCTION

Multiple chronic ulcers of small intestine are mainly ascribed to Crohn's disease. Among possible differential diagnoses are chronic ulcers of small bowel caused by abnormal activation of the prostaglandin pathway either in the archetypal but uncommon non-steroidal anti-inflammatory drug (NSAID)-induced enteropathy, or in rare monogenic disorders due to PLA2G4A and SLCO2A1 mutations. SLCO2A1 variants are responsible for CEAS (Chronic enteropathy associated with SLCO2A1), a syndrome which was exclusively reported in patients of Asian origin. Herein, we report the case of two French female siblings with CEAS.

CASE REPORT

P1 underwent iterative bowel resections (removing 1 meter of small bowel in total) for recurrent strictures and perforations. Her sister P2 had a tight duodenal stricture which required partial duodenectomy. Next-generation sequencing was performed on P1's DNA and identified 2 compound heterozygous variants in exon 12 in SLCO2A1, which were also present in P2.

CONCLUSION

CEAS can be detected within the European population and raise the question of its incidence and recognition outside Asia. Presence of intractable recurrent ulcerations of the small intestine mimicking Crohn's disease with concentric stricture should motivate a genetic search for SLCO2A1 mutations, particularly in the context of family history or consanguinity.

Understanding Musculoskeletal Disorders Through Next-Generation Sequencing

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An insight into musculoskeletal disorders through advancements in next-generation sequencing (NGS) promises to maximize benefits and improve outcomes through improved genetic diagnosis.

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The primary use of whole exome sequencing (WES) for musculoskeletal disorders is to identify functionally relevant variants.

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The current evidence has shown the superiority of NGS over conventional genotyping for identifying novel and rare genetic variants in patients with musculoskeletal disorders, due to its high throughput and low cost.

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Genes identified in patients with scoliosis, osteoporosis, osteoarthritis, and osteogenesis imperfecta using NGS technologies are listed for further reference.

Bone Geometry, Density, Microstructure, and Biomechanical Properties in the Distal Tibia in Patients With Primary Hypertrophic Osteoarthropathy Assessed by Second-Generation High-Resolution Peripheral Quantitative Computed Tomography

Periosteosis refers to pathological woven bone formation beneath the cortical bone of the long bones. It is an imaging hallmark of primary hypertrophic osteoarthropathy (PHO) and also considered as one of the major diagnostic criteria of PHO patients. Up to date, detailed information on bone quality changes in long bones of PHO patients is still missing. This study aimed to evaluate bone microarchitecture and bone strength in PHO patients by using high-resolution peripheral quantitative computed tomography (HR-pQCT). The study comprised 20 male PHO patients with the average age of 27.0 years and 20 age- and sex-matched healthy controls. The areal bone mineral density (aBMD) was assessed at the lumbar spine (L₁ -L₄ ) and hip (total hip and femoral neck) by dual-energy X-ray absorptiometry (DXA). Bone geometry, volumetric bone mineral density (vBMD), and microstructure parameters at the distal tibia were evaluated by using HR-pQCT. Bone strength was evaluated by finite element analysis (FEA) based on HR-pQCT screening at distal tibia. Urinary prostaglandin E₂ (PGE₂ ), serum phosphatase (ALP), beta-C-telopeptides of type I collagen (β-CTX), soluble receptor activator of nuclear factor-κB ligand (sRANKL), osteoprotegerin (OPG), and neuronal calcitonin gene-related peptide (CGRP) were investigated. As compared with healthy controls, PHO patients had larger bone cross-sectional areas; lower total, trabecular, and cortical vBMD; compromised bone microstructures with more porous cortices, thinned trabeculae, reduced trabecular connectivity, and relatively more significant resorption of rod-like trabeculae at distal tibia. The apparent Young's modulus was significantly lower in PHO patients. The concentration of PGE₂ , biomarkers of bone resorption (β-CTX and sRANKL/OPG ratio), and the neuropeptide CGRP were higher in PHO patients versus healthy controls. PGE₂ level correlated negatively with vBMD and estimated bone strength and positively with bone geometry at distal tibia. The present HR-pQCT study is the first one illustrating the microarchitecture and bone strength features in long bones. © 2021 American Society for Bone and Mineral Research (ASBMR).

Recent advances in studies of 15-PGDH as a key enzyme for the degradation of prostaglandins

15-hydroxyprostaglandin dehydrogenase (15-PGDH; encoded by HPGD) is ubiquitously expressed in mammalian tissues and catalyzes the degradation of prostaglandins (PGs; mainly PGE2, PGD2, and PGF2α) in a process mediated by solute carrier organic anion transport protein family member 2A1 (SLCO2A1; also known as PGT, OATP2A1, PHOAR2, or SLC21A2). As a key enzyme, 15-PGDH catalyzes the rapid oxidation of 15-hydroxy-PGs into 15-keto-PGs with lower biological activity. Increasing evidence suggests that 15-PGDH plays a key role in many physiological and pathological processes in mammals and is considered a potential pharmacological target for preventing organ damage, promoting bone marrow graft recovery, and enhancing tissue regeneration. Additionally, results of whole-exome analyses suggest that recessive inheritance of an HPGD mutation is associated with idiopathic hypertrophic osteoarthropathy. Interestingly, as a tumor suppressor, 15-PGDH inhibits proliferation and induces the differentiation of cancer cells (including those associated with colorectal, lung, and breast cancers). Furthermore, a recent study identified 15-PGDH as a marker of aging tissue and a potential novel therapeutic target for resisting the complex pathology of aging-associated diseases. Here, we review and summarise recent information on the molecular functions of 15-PGDH and discuss its pathophysiological implications.

Monoallelic mutations in SLCO2A1 cause autosomal dominant primary hypertrophic osteoarthropathy

Primary hypertrophic osteoarthropathy (PHO) is a rare disease inherited as a recessive or irregular dominant trait and characterized by digital clubbing, pachydermia, and periostosis. Biallelic mutations in HPGD and SLCO2A1, disturbing prostaglandin E₂ (PGE₂ ) catabolism and leading to increased circulating PGE₂ level, cause PHO autosomal recessive 1 (PHOAR1) and PHO autosomal recessive 2 (PHOAR2), respectively. However, no causative genes have been reported for PHO autosomal dominant (PHOAD). Here, we performed Sanger sequencing and whole-genome sequencing (WGS) on DNA samples from seven Chinese PHOAD families; after excluding other single-nucleotide variants (SNVs), structural variations (SVs), and copy number variations (CNVs) in the genomes, we reported six SLCO2A1 monoallelic mutations (c.1660G>A [p.G554R], c.664G>A [p.G222R], c.1106G>A [p.G369D], c.1065dupA [p.Q356TfsX77], c.1293delT [p.S432AfsX48], and c.1807C>T [p.R603X]) in the probands and affected family members. Then, in five other PHO families with probands carrying SLCO2A1 biallelic mutations, we verified that parents with SLCO2A1 monoallelic mutations also displayed PHO manifestations, which further confirmed the pathogenicity of SLCO2A1 monoallelic mutations and illustrated the allelic nature of PHOAD and PHOAR2. Subsequently, through comparison of seven PHOAD probands and 50 PHOAR2 patients, we found onset age in puberty and skewed penetrance rate were similar in both PHO types, but symptoms and signs of PHOAD were milder, including less severe pachydermia (p = .027) and periostosis (p = .005), and less frequent cutis verticis gyrata (p = .011), acne (p = .005), arthralgia (p = .037), and anemia (p = .023). The median urinary PGE₂ level in PHOAD probands was almost half that in PHOAR2 patients (PHOAD 277.58 ng/mmoL creatinine, PHOAR2 473.19 ng/mmoL creatinine; p = .038). Moreover, through the 3-month trial of oral administration of etoricoxib, an effective response similar to that we reported previously in PHOAR2 patients was observed in PHOAD probands. In conclusion, our findings confirm that SLCO2A1 monoallelic mutations are the cause of PHOAD and broaden phenotypic spectrum of PHO. © 2021 American Society for Bone and Mineral Research (ASBMR).

Eicosanoid profiling in patients with complete form of pachydermoperiostosis carrying SLCO2A1 mutations

Pachydermoperiostosis (PDP) is a genetic disease characterized by digital clubbing, periostosis, and pachydermia caused by mutated HPGD or SLCO2A1. Plasma prostaglandin (PG)E₂ levels are increased in these patients. However, other eicosanoids have not been quantitated. We aimed to quantitate plasma eicosanoid levels in four patients carrying SLCO2A1 mutations by high-performance liquid chromatography-tandem mass spectrometry. PGE₂ level was elevated in all patients; PGD₂ and 11β-PGF₂ α levels were also increased in some patients, whereas eicosapentaenoic acid, docosahexaenoic acid, and arachidonic acid levels were decreased in all patients. Our data indicate a dysfunctional eicosanoid homeostasis and varied levels of PG in patients with a complete form of PDP carrying SLCO2A1 mutations. PGE₂ levels seem to mostly affect the symptoms, with other eicosanoids possibly having a minor effect.

Recent advances in studies of SLCO2A1 as a key regulator of the delivery of prostaglandins to their sites of action

Solute carrier organic anion transporter family member 2A1 (SLCO2A1, also known as PGT, OATP2A1, PHOAR2, or SLC21A2) is a plasma membrane transporter consisting of 12 transmembrane domains. It is ubiquitously expressed in tissues, and mediates the membrane transport of prostaglandins (PGs, mainly PGE₂, PGF_2α, PGD₂) and thromboxanes (e.g., TxB₂). SLCO2A1-mediated transport is electrogenic and is facilitated by an outwardly directed gradient of lactate. PGs imported by SLCO2A1 are rapidly oxidized by cytoplasmic 15-hydroxyprostaglandin dehydrogenase (15-PGDH, encoded by HPGD). Accumulated evidence suggests that SLCO2A1 plays critical roles in many physiological processes in mammals, and it is considered a potential pharmacological target for diabetic foot ulcer treatment, antipyresis, and non-hormonal contraception. Furthermore, whole-exome analyses suggest that recessive inheritance of SLCO2A1 mutations is associated with two refractory diseases, primary hypertrophic osteoarthropathy (PHO) and chronic enteropathy associated with SLCO2A1 (CEAS). Intriguingly, SLCO2A1 is also a key component of the Maxi-Cl channel, which regulates fluxes of inorganic and organic anions, including ATP. Further study of the bimodal function of SLCO2A1 as a transporter and ion channel is expected to throw new light on the complex pathology of human diseases. Here, we review and summarize recent information on the molecular functions of SLCO2A1, and we discuss its pathophysiological significance.

A novel mutation in the SLCO2A1 gene, encoding a prostaglandin transporter, induces chronic enteropathy

Chronic enteropathy associated with SLCO2A1 gene (CEAS) is caused by loss-of-function mutations in SLCO2A1, which encodes a prostaglandin (PG) transporter. In this study, we report a sibling case of CEAS with a novel pathogenic variant of the SLCO2A1 gene. Compound heterozygous variants in SLCO2A1 were identified in an 8-year-old boy and 12-year-old girl, and multiple chronic nonspecific ulcers were observed in the patients using capsule endoscopy. The splice site mutation (c.940 + 1G>A) of the paternal allele was previously reported to be pathogenic, whereas the missense variant (c.1688T>C) of the maternal allele was novel and had not yet been reported. The affected residue (p.Leu563Pro) is located in the 11th transmembrane domain (helix 11) of SLCO2A1. Because SLCO2A1 mediates the uptake and clearance of PGs, the urinary PG metabolites were measured by liquid chromatography coupled to tandem mass spectrometry. The urinary tetranor-prostaglandin E metabolite levels in the patients were significantly higher than those in unaffected individuals. We established cell lines with doxycycline-inducible expression of wild type SLCO2A1 (WT-SLCO2A1) and the L563P mutant. Immunofluorescence staining showed that WT-SLCO2A1 and the L563P mutant were dominantly expressed on the plasma membranes of these cells. Cells expressing WT-SLCO2A1 exhibited time- and dose-dependent uptake of PGE₂, while the mutant did not show any uptake activity. Residue L563 is very close to the putative substrate-binding site in SLCO2A1, R561 in helix 11. However, in a molecular model of SLCO2A1, the side chain of L563 projected outside of helix 11, indicating that L563 is likely not directly involved in substrate binding. Instead, the substitution of Pro may twist the helix and impair the transporter function. In summary, we identified a novel pathogenic variant of SLCO2A1 that caused loss-of-function and induced CEAS.

Digital clubbing as the predominant manifestation of hypertrophic osteoarthropathy caused by pathogenic variants in HPGD in three Indian families

15-Hydroxyprostaglandin dehydrogenase is NAD-dependent catalytic enzyme involved in prostaglandin biosynthesis pathway encoded by HPGD. The pathogenic variations in HPGD cause primary hypertrophic osteoarthropathy (PHO). The objective of the present study is to identify the genetic basis in patients with digital clubbing due to PHO. We performed detailed clinical and radiographic evaluation and exome sequencing in patients from three unrelated Indian families with PHO. Exome sequencing revealed two novel, c.34G>A (p.Gly12Ser) and c.313C>T (p.Gln105*) and a known variant, c.418G>C (p.Ala140Pro) in HPGD. Herein, we add three Indian families to HPGD mutation spectrum and review the literature on variants in this gene.

Characterization of Mineral and Bone Metabolism Biomarkers in a Chinese Consanguineous Twin Family with Primary Hypertrophic Osteoarthropathy

PURPOSE

Primary hypertrophic osteoarthropathy (PHO) is a rare, autosomal, recessive genetic disease characterized by digital clubbing, periostosis, and pachydermia. The underlying cause for the pathogenesis of this disease is a defect in prostaglandin E2 (PGE2) degradation, caused by mutations in HPGD or SLCO2A1. In this study, we describe the clinical characteristics, SLCO2A1 mutations, and bone metabolic markers of a PHO pedigree from a Chinese consanguineous twin family.

METHODS

Whole blood and urine samples were collected from all the family members. All the exons and exon-intron boundaries of the HPGD and SLCO2A1 genes were amplified using polymerase chain reaction (PCR) and sequenced. The biomarkers of mineral and bone metabolism, including calcium, phosphorus, parathyroid hormone (PTH), 25-hydroxyvitamin D (25(OH)D), bone Gla-protein (BGP), C-terminal telopeptide of type I collagen (β-CTX), and urinary calcium/creatinine ratio (Uca/Ucr) were detected.

RESULTS

A homozygous (nonsense) mutation in the SLCO2A1 gene (c.1807C >T/p.R603 ^∗ ) was detected in the proband. Five heterozygous carriers were also identified among his relatives, including his twin brother. The serum BGP (225.5 ng/ml), β-CTX (4112 pg/ml), and Uca/Ucr (0.63) levels were significantly elevated, while the 25(OH)D (37.1 nmol/L) level was reduced in the proband. The proband's twin brother displayed increased levels of β-CTX (901 pg/ml) and insufficiency of 25(OH)D (67.29 nmol/L), while the other heterozygous carriers only displayed 25(OH)D insufficiency.

CONCLUSION

The patients with PHO displayed an active state of bone reconstruction. There may be a lack of vitamin D, accompanied by an increase in BGP and β-CTX levels. Heterozygous mutations of SLCO2A1 might lead to mild PHO.

Impaired bone microarchitecture in distal interphalangeal joints in patients with primary hypertrophic osteoarthropathy assessed by high-resolution peripheral quantitative computed tomography

This study aimed to investigate the bone impairment in finger joints in PHO patients by HR-pQCT. Results showed distinguished differences in bone architecture and biomechanics parameters at DIPs between PHO patients and healthy controls using HR-pQCT assessment. Besides, serum PGE2, hsCRP and ESR levels were found negatively correlated with total vBMD.

INTRODUCTION

This study aimed to investigate the bone impairment in finger joints in primary hypertrophic osteoarthropathy (PHO) patients firstly by high-resolution peripheral quantitative computed tomography (HR-pQCT).

METHODS

Fifteen PHO patients and 15 healthy controls were enrolled in this study. Bone erosions in hands at distal interphalangeal joints (DIPs) in both PHO patients and controls were evaluated by X-ray. Bone geometry, vBMD, microstructure parameters, and size of individual bone erosion were also measured at the 3rd DIP by HR-pQCT as well. Blood biochemistry levels between the two groups were also compared.

RESULTS

Compared to X-ray, HR-pQCT assessment were more sensitive for detection of bone erosions, with 14 PHO patients by HR-pQCT versus ten PHO patients by X-ray judged at the 3rd DIP. The average depth, width, and volume of erosions size in PHO patients were 1.38 ± 0.80 mm, 0.79 ± 0.27 mm, and 1.71 ± 0.52 mm³, respectively. The bone cross-areas including total area (+ 25.3%, p ≤ 0.05), trabecular area (+ 56.2%, p ≤ 0.05), and cortical perimeter (+ 10.7%, p ≤ 0.05) at the defined region of interest of 3rd DIP was significantly larger than controls. Total vBMD was 11.9% lower in PHO patients compared with the controls (p ≤ 0.05). Biochemical test results showed the increased levels of inflammatory cytokines, bone resorption markers, and joint degeneration markers in PHO patients. Serum prostaglandin PGE2, high-sensitive C-reactive protein (hsCRP) and erythrocyte sedimentation rate (ESR) levels were found negatively correlated with total vBMD.

CONCLUSIONS

This study demonstrated higher sensitivity of the HR-pQCT measurement at DIPs by showing the differences in architecture and biomechanics parameters at DIPs between the PHO patients and healthy controls, which would be of interest clinically to investigate bone deterioration in PHO patients.

Primary hypertrophic osteoarthropathy related gastrointestinal complication has distinctive clinical and pathological characteristics: two cases report and review of the literature

BACKGROUND

Primary hypertrophic osteoarthropathy (PHO) is a rare disease related to HPGD and SLCO2A1 gene mutation. Gastrointestinal involvement of PHO is even rarer with unknown pathogenesis. Clinical features of GI complication in PHO mimics other auto-immune based bowel entities, such as inflammatory bowel diseases and cryptogenic multifocal ulcerous stenosing enteritis (CMUSE). We aimed to analyze the clinical, genetic, radiological and pathological features of Chinese patients with PHO and determine the difference between PHO patients presenting with and without GI involvement.

METHODS

We reported two PHO cases with gastrointestinal involvement and reviewed all the studies of PHO in Chinese population published from January 1, 2000, to April 30, 2018. Clinical and genetic presentations of PHO in Chinese patients were analyzed. We compared the characteristics of those patients with gastrointestinal involvement against those without.

RESULTS

The two patients were both males with complete-form PHO for more than 10 years. GI related symptoms included diarrhea, chronic gastrointestinal hemorrhage, incomplete intestinal obstruction, anemia, and edema, which were unresponsive to etoricoxib treatment. Radiological examinations revealed segmental intestinal stenosis and thickened intestinal wall. Endoscopic findings included multiple ulcers and mucosal inflammation. Both patients had mutations of SLCO2A1 according to sequence analysis. The surgical pathology revealed chronic inflammation involving the intestinal mucosa and submucosa, similar to histological changes in CMUSE. According to the systemic review of 158 Chinese patients with PHO, 17.2% had gastrointestinal involvement, including peptic ulcer, gastric polyps, hypertrophic gastritis, and segmental intestinal stenosis. Patients with gastrointestinal involvement were more likely to have anemia (40.0% vs. 4.5%, P < 0.001), hypoalbuminemia (16.7% vs. 0.9%, P = 0.003), and myelofibrosis (19.0% vs. 0.9%, P = 0.002) than those without. Most patients with gastrointestinal complication had SLCO2A1 mutation (86.7%, 13 /15).

CONCLUSIONS

Digestive tract involvement is uncommon in patients with PHO and often presents with anemia, and hypoalbuminemia resulted from intestinal inflammation. The intestinal pathologic characteristics are distinct from Crohn's disease but similar to CMUSE. Mutations in SLCO2A1 might be the pathogenic cause of GI involvement of PHO. NSAIDs may not be effective for PHO patients with gastrointestinal complications.

Novel SLCO2A1compound heterozygous mutation causing primary hypertrophic osteoarthropathy with Bartter-like hypokalemia in a Chinese family

PURPOSE

Primary hypertrophic osteoarthropathy (PHO) is an inherited disease characterized by digital clubbing, periostosis and pachydermia with defects in the degradation of prostaglandin E2 (PGE2). Mutations in SLCO2A1 gene-encoding prostaglandin transporter (PGT) resulted in PHO, autosomal recessive 2 (PHOAR2). The spectrum of mutations and variable clinical complications of PHOAR2 has been delineated. In this study, we investigated a Chinese PHO family with a manifestation of Bartter-like hypokalemia.

METHODS

Clinical manifestations were collected and genetic analyses were performed in the PHO family.

RESULTS

The 33-year-old male proband had severe hypokalemia due to potassium loss from the kidney, while his brother had mild hypokalemia. After being treated with etoricoxib, the serum potassium level of the patient increased rapidly to the normal range which corresponded with the reduction in his serum PGE2 and PE2 metabolite (PGEM) levels. A novel SLCO2A1 compound heterozygous mutation of p.I284V and p.C459R was identified in two PHO patients in this family.

CONCLUSIONS

The present findings supported that the Bartter-like hypokalemia is a new complication of PHOAR2 caused by the high level of PGE2. Etoricoxib was demonstrated to be effective for the renal hypokalemia in PHO patients.

The first case of primary hypertrophic osteoarthropathy with soft tissue giant tumors caused by HPGD loss-of-function mutation

BACKGROUND

Primary hypertrophic osteoarthropathy (PHO) is a rare genetic multi-organic disease characterized by digital clubbing, periostosis and pachydermia. Two genes, HPGD and SLCO2A1, which encodes 15-hydroxyprostaglandin dehydrogenase (15-PGDH) and prostaglandin transporter (PGT), respectively, have been reported to be related to PHO. Deficiency of aforementioned two genes leads to failure of prostaglandin E2 (PGE2) degradation and thereby elevated levels of PGE2. PGE2 plays an important role in tumorigenesis. Studies revealed a tumor suppressor activity of 15-PGDH in tumors, such as lung, bladder and breast cancers. However, to date, no HPGD-mutated PHO patients presenting concomitant tumor has been documented. In the present study, we reported the first case of HPGD-mutated PHO patient with soft tissue giant tumors at lower legs and evaluated the efficacy of selective COX-2 inhibitor (etoricoxib) treatment in the patient.

METHODS

In this study, we summarized the clinical data, collected the serum and urine samples for biochemical test and analyzed the HPGD gene in our patient.

RESULTS

A common HPGD mutation c.310_311delCT was identified in the patient. In addition to typical clinical features (digital clubbing, periostosis and pachydermia), the patient demonstrated a new clinical manifestation, a giant soft tissue tumor on the left lower leg which has not been reported in HPGD-mutated PHO patient before. After 6-month treatment with etoricoxib, the patient showed decreased PGE2 levels and improved PHO-related symptoms. Though the soft tissue tumor persisted, it seemed to be controlled under the etoricoxib treatment.

CONCLUSION

This finding expanded the clinical spectrum of PHO and provided unique insights into the HPGD-mutated PHO.

Pachydermoperiostosis: A clinicopathological description

Purpose

To report a case of pachydermoperiostosis (PDP) and a review of the literature.

Methods

A 32-year-old man was referred to our clinic with bilateral eyelid swelling and blepharoptosis. On examination, marked blepharoptosis was noted, and his eyelids were found to be floppy. Systemic examination was significant for clubbing of digits, coarse acromegalic facial features, and furrowing and oiliness of the skin of scalp and forehead.

Results

The patient was diagnosed as a case of PDP. On the brain MRI, the pituitary gland was enlarged, and the border of clivus was irregular. Pituitary and thyroid hormone levels were normal. He underwent bilateral lateral tarsal strip (LTS) procedure to address the eyelid laxity. Histopathologic examination revealed marked sebaceous gland hyperplasia with mucin deposition in the dermis.

Conclusion

Floppy eyelid syndrome, clubbing, and acromegaloid face are main features that could lead to the diagnosis of PDP.

Safety and efficacy of cyclooxygenase-2 inhibition for treatment of primary hypertrophic osteoarthropathy: A single-arm intervention trial

Background

Primary hypertrophic osteoarthropathy (PHO) is a rare disease involving joint, bone and skin. Two underlying genes responsible for this disease-hydroxyprostaglandin dehydrogenase (HPGD) and solute carrier organic anion transporter family, member 2A1 (SLCO2A1)-are both associated with aberrant accumulation of prostaglandin E2 (PGE2). Cyclooxygenase-2 (COX-2) is a key enzyme in PGE2 synthesis. This study was intended to evaluate the safety and efficacy of COX-2 inhibitor in the treatment of PHO.

Methods

We recruited patients presenting to Peking Union Medical Hospital between January 2009 and December 2016 who were diagnosed with PHO. Participants were given the COX-2 inhibitor etoricoxib (60 mg once daily) and followed up for 9 months. Gene analysis was performed at baseline. The following data were collected at baseline and during treatment: visual analogue score (VAS), volume of the distal middle finger (VDMF), knee joint circumference (KJC), serum and urinary levels of prostaglandin E2 (PGE2) and PGE metabolite (PGE-M) and serum levels of inflammatory markers.

Results

A total of 27 patients were recruited, including seven patients with PHO type I (PHOAR1) carrying HPGD gene mutations and 20 patients with PHO type II (PHOAR2) carrying SLCO2A1 gene mutations. After treatment with etoricoxib, the majority of patients experienced resolution of symptoms including pachydermia (60.9%), joint swelling (100%), digital clubbing (74.1%) and hyperhidrosis (55.0%). In both the PHO subtypes, serum and urinary levels of PGE2 were elevated at baseline and declined sharply upon treatment. For PHOAR1 patients, serum and urinary PGE-M levels were relatively low and demonstrated minimal response to COX-2 inhibition. Among PHOAR2 patients, mean serum and urinary levels of PGE-M presented at a high level at baseline and were normalized after 3 months of treatment. No severe adverse effects were reported during the study period.

Conclusions

We found COX-2 inhibitor to be safe and effective for the treatment of PHO in our cohort.

The translational potential of this article

The underlying genes responsible for PHO suggest COX inhibitor as potential therapy, and our study demonstrates the efficacy and safety of this treatment.

Novel SLCO2A1 mutations cause gender differentiated pachydermoperiostosis

Primary hypertrophic osteoarthropathy (PHO) is a rare familial disorder with reduced penetrance for females. The genetic mutations associated with PHO have been identified in HPGD and SLCO2A1 which involved in prostaglandin E2 metabolism. Here we report 5 PHO patients from 4 non-consanguineous families. Two heterozygous mutations in solute carrier organic anion transporter family member 2A1 (SLCO2A1) were identified in two brothers by whole-exome sequencing. Three heterozygous mutations and 1 homozygous mutation were identified in other 3 PHO families by Sanger sequencing. However, there was no mutation in HPGD. These findings confirmed that homozygous or compound heterozygous mutations of SLCO2A1 were the pathogenic cause of PHO. A female individual shared the same mutations in SLCO2A1 with her PHO brother but did not have any typical PHO symptoms. The influence of sex hormones on the pathogenesis of PHO and its implication were discussed.