Penttinen syndrome-associated PDGFRB Val665Ala variant causes aberrant constitutive STAT1 signalling.

Penttinen syndrome is a rare progeroid disorder caused by mutations in platelet-derived growth factor (PDGF) receptor beta (encoded by the PDGFRB proto-oncogene) and characterized by a prematurely aged appearance with lipoatrophy, skin lesions, thin hair and acro-osteolysis. Activating mutations in PDGFRB have been associated with other human diseases, including Kosaki overgrowth syndrome, infantile myofibromatosis, fusiform aneurysms, acute lymphoblastic leukaemia and myeloproliferative neoplasms associated with eosinophilia. The goal of the present study was to characterize the PDGFRB p.Val665Ala variant associated with Penttinen syndrome at the molecular level. This substitution is located in a conserved loop of the receptor tyrosine kinase domain. We observed that the mutant receptor was expressed at a lower level but showed constitutive activity. In the absence of ligand, the mutant activated STAT1 and elicited an interferon-like transcriptional response. Phosphorylation of STAT3, STAT5, AKT and phospholipase Cγ was weak or undetectable. It was devoid of oncogenic activity in two cell proliferation assays, contrasting with classical PDGF receptor oncogenic mutants. STAT1 activation was not sensitive to ruxolitinib and did not rely on interferon-JAK2 signalling. Another tyrosine kinase inhibitor, imatinib, blocked signalling by the p.Val665Ala variant at a higher concentration compared with the wild-type receptor. Importantly, this concentration remained in the therapeutic range. Dasatinib, nilotinib and ponatinib also inhibited the mutant receptor. In conclusion, the p.Val665Ala variant confers unique features to PDGF receptor ß compared with other characterized gain-of-function mutants, which may in part explain the particular set of symptoms associated with Penttinen syndrome.

Severe hypercalcaemia early after kidney transplantation in two patients with severe secondary hyperparathyroidism previously treated with etelcalcetide.

Cinacalcet and, more recently, etelcalcetide revolutionized the treatment of chronic kidney disease-mineral and bone disorder (CKD-MBD). Kidney transplant (KT) usually improves CKD-MBD. However, a significant proportion of KT recipients have high serum calcium levels, not requiring any treatment. We report two patients previously treated with etelcalcetide who developed severe (>3.3 mmol/L) hypercalcaemia in the early post-KT course, requiring parathyroidectomy. Pathological studies showed parathyroid adenomas and hyperplasia. One patient had a graft biopsy showing numerous intratubular calcium phosphate crystals. These observations should prompt pharmacovigilance studies and careful follow-up of KT recipients previously treated with etelcalcetide.

Novel COL4A1-VEGFD gene fusion in myofibroma.

Myofibroma is a benign pericytic tumour affecting young children. The presence of multicentric myofibromas defines infantile myofibromatosis (IMF), which is a life-threatening condition when associated with visceral involvement. The disease pathophysiology remains poorly characterized. In this study, we performed deep RNA sequencing on eight myofibroma samples, including two from patients with IMF. We identified five different in-frame gene fusions in six patients, including three previously described fusion transcripts, SRF-CITED1, SRF-ICA1L and MTCH2-FNBP4, and a fusion of unknown significance, FN1-TIMP1. We found a novel COL4A1-VEGFD gene fusion in two cases, one of which also carried a PDGFRB mutation. We observed a robust expression of VEGFD by immunofluorescence on the corresponding tumour sections. Finally, we showed that the COL4A1-VEGFD chimeric protein was processed to mature VEGFD growth factor by proteases, such as the FURIN proprotein convertase. In conclusion, our results unravel a new recurrent gene fusion that leads to VEGFD production under the control of the COL4A1 gene promoter in myofibroma. This fusion is highly reminiscent of the COL1A1-PDGFB oncogene associated with dermatofibrosarcoma protuberans. This work has implications for the diagnosis and, possibly, the treatment of a subset of myofibromas.

PDGF receptor mutations in human diseases.

PDGFRA and PDGFRB are classical proto-oncogenes that encode receptor tyrosine kinases responding to platelet-derived growth factor (PDGF). PDGFRA mutations are found in gastrointestinal stromal tumors (GISTs), inflammatory fibroid polyps and gliomas, and PDGFRB mutations drive myofibroma development. In addition, chromosomal rearrangement of either gene causes myeloid neoplasms associated with hypereosinophilia. Recently, mutations in PDGFRB were linked to several noncancerous diseases. Germline heterozygous variants that reduce receptor activity have been identified in primary familial brain calcification, whereas gain-of-function mutants are present in patients with fusiform aneurysms, Kosaki overgrowth syndrome or Penttinen premature aging syndrome. Functional analysis of these variants has led to the preclinical validation of tyrosine kinase inhibitors targeting PDGF receptors, such as imatinib, as a treatment for some of these conditions. This review summarizes the rapidly expanding knowledge in this field.

Genetic testing and surveillance in infantile myofibromatosis: a report from the SIOPE Host Genome Working Group.

Infantile myofibromatosis (IM), which is typically diagnosed in young children, comprises a wide clinical spectrum ranging from inconspicuous solitary soft tissue nodules to multiple disseminated tumors resulting in life-threatening complications. Familial IM follows an autosomal dominant mode of inheritance and is linked to PDGFRB germline variants. Somatic PDGFRB variants were also detected in solitary and multifocal IM lesions. PDGFRB variants associated with IM constitutively activate PDGFRB kinase activity in the absence of its ligand. Germline variants have lower activating capabilities than somatic variants and, thus, require a second cis-acting hit for full receptor activation. Typically, these mutant receptors remain sensitive to tyrosine kinase inhibitors such as imatinib. The SIOPE Host Genome Working Group, consisting of pediatric oncologists, clinical geneticists and scientists, met in January 2020 to discuss recommendations for genetic testing and surveillance for patients who are diagnosed with IM or have a family history of IM/PDGFRB germline variants. This report provides a brief review of the clinical manifestations and genetics of IM and summarizes our interdisciplinary recommendations.

Inflammation-induced cholestasis in cancer cachexia.

BACKGROUND: Cancer cachexia is a debilitating metabolic syndrome contributing to cancer death. Organs other than the muscle may contribute to the pathogenesis of cancer cachexia. This work explores new mechanisms underlying hepatic alterations in cancer cachexia. METHODS: We used transcriptomics to reveal the hepatic gene expression profile in the colon carcinoma 26 cachectic mouse model. We performed bile acid, tissue mRNA, histological, biochemical, and western blot analyses. Two interventional studies were performed using a neutralizing interleukin 6 antibody and a bile acid sequestrant, cholestyramine. Our findings were evaluated in a cohort of 94 colorectal cancer patients with or without cachexia (43/51). RESULTS: In colon carcinoma 26 cachectic mice, we discovered alterations in five inflammatory pathways as well as in other pathways, including bile acid metabolism, fatty acid metabolism, and xenobiotic metabolism (normalized enrichment scores of -1.97, -2.16, and -1.34, respectively; all Padj < 0.05). The hepatobiliary transport system was deeply impaired in cachectic mice, leading to increased systemic and hepatic bile acid levels (+1512 ± 511.6 pmol/mg, P = 0.01) and increased hepatic inflammatory cytokines and neutrophil recruitment to the liver of cachectic mice (+43.36 ± 16.01 neutrophils per square millimetre, P = 0.001). Adaptive mechanisms were set up to counteract this bile acid accumulation by repressing bile acid synthesis and by enhancing alternative routes of basolateral bile acid efflux. Targeting bile acids using cholestyramine reduced hepatic inflammation, without affecting the hepatobiliary transporters (e.g. tumour necrosis factor α signalling via NFκB and inflammatory response pathways, normalized enrichment scores of -1.44 and -1.36, all Padj < 0.05). Reducing interleukin 6 levels counteracted the change in expression of genes involved in the hepatobiliary transport, bile acid synthesis, and inflammation. Serum bile acid levels were increased in cachectic vs. non-cachectic cancer patients (e.g. total bile acids, +5.409 ± 1.834 µM, P = 0.026) and were strongly correlated to systemic inflammation (taurochenodeoxycholic acid and C-reactive protein: ρ = 0.36, Padj = 0.017). CONCLUSIONS: We show alterations in bile acid metabolism and hepatobiliary secretion in cancer cachexia. In this context, we demonstrate the contribution of systemic inflammation to the impairment of the hepatobiliary transport system and the role played by bile acids in the hepatic inflammation. This work paves the way to a better understanding of the role of the liver in cancer cachexia.

Diagnostic limitations and considerations in the imaging evaluation of advanced multicentric infantile myofibromatosis.

Infantile myofibromatosis, the most common fibrous tumor of infancy, is classified in 2 forms; as a solitary nodule or as numerous, widely-distributed multicentric lesions with or without visceral involvement. Although benign, multicentric myofibromas are still associated with a high incidence of morbidity and mortality due to the infiltration of critical structures. Herein, we present a case of an infant with aggressive PDGFRB and NOTCH3 mutation-negative myofibromas distributed throughout the vascular, respiratory, and gastrointestinal systems. The extensive disease resulted in pulmonary hypertension, respiratory failure and gastrointestinal obstruction refractory to chemotherapy and unamenable to surgical resection. Despite the presence of numerous highly invasive myofibromas, multiple imaging modalities largely underestimated, or even missed, tumors found at autopsy. This case demonstrates the limitations of radiographic imaging to assess disease burden in multicentric infantile myofibromatosis. The postmortem findings of extensive disease far exceeding what was demonstrated by multiple imaging modalities suggests that pediatricians should have a high index of suspicion for undetected tumors if clinical deterioration is otherwise unexplained.

Association of PDGFRB Mutations With Pediatric Myofibroma and Myofibromatosis.

IMPORTANCE: Myofibroma is the most frequent fibrous tumor in children. Multicentric myofibroma (referred to as infantile myofibromatosis) is a life-threatening disease. OBJECTIVE: To determine the frequency, spectrum, and clinical implications of mutations in the PDGFRB receptor tyrosine kinase found in sporadic myofibroma and myofibromatosis. DESIGN, SETTING, AND PARTICIPANTS: In this retrospective study of 69 patients with sporadic myofibroma or myofibromatosis, 85 tumor samples were obtained and analyzed by targeted deep sequencing of PDGFRB. Mutations were confirmed by an alternative method of sequencing and were experimentally characterized to confirm gain of function and sensitivity to the tyrosine kinase inhibitor imatinib. MAIN OUTCOMES AND MEASURES: Frequency of gain-of-function PDGFRB mutations in sporadic myofibroma and myofibromatosis. Sensitivity to imatinib, as assessed experimentally. RESULTS: Of the 69 patients with tumor samples (mean [SD] age, 7.8 [12.7] years), 60 were children (87%; 29 girls [48%]) and 9 were adults (13%; 4 women [44%]). Gain-of-function PDGFRB mutations were found in samples from 25 children, with no mutation found in samples from adults. Mutations were particularly associated with severe multicentric disease (13 of 19 myofibromatosis cases [68%]). Although patients had no familial history, 3 of 25 mutations (12%) were likely to be germline, suggesting de novo heritable alterations. All of the PDGFRB mutations were associated with ligand-independent receptor activation, and all but one were sensitive to imatinib at clinically relevant concentrations. CONCLUSIONS AND RELEVANCE: Gain-of-function mutations of PDGFRB in myofibromas may affect only children and be more frequent in the multicentric form of disease, albeit present in solitary pediatric myofibromas. These alterations may be sensitive to tyrosine kinase inhibitors. The PDGFRB sequencing appears to have a high value for diagnosis, prognosis, and therapy of soft-tissue tumors in children.

PDGFRB gain-of-function mutations in sporadic infantile myofibromatosis.

Infantile myofibromatosis is one of the most prevalent soft tissue tumors of infancy and childhood. Multifocal nodules with visceral lesions are associated with a poor prognosis. A few familial cases have been linked to mutations in various genes including PDGFRB. In this study, we sequenced PDGFRB, which encodes a receptor tyrosine kinase, in 16 cases of myofibromatosis or solitary myofibroma. Mutations in the coding sequence of PDGFRB were identified in 6 out of 8 patients with the sporadic multicentric form of the disease and in 1 out of 8 patients with isolated myofibroma. Two patients had the same mutation in multiple separated lesions. By contrast, a third patient had three different PDGFRB mutations in the three nodules analyzed. Mutations were located in the transmembrane, juxtamembrane and kinase domains of the receptor. We showed that these mutations activated receptor signaling in the absence of ligand and transformed fibroblasts. In one case, a weakly-activating germline variant was associated with a stronger somatic mutation, suggesting a two-hit model for familial myofibromatosis. Furthermore, the mutant receptors were sensitive to the tyrosine kinase inhibitor imatinib, except D850V, which was inhibited by dasatinib and ponatinib, suggesting a targeted therapy for severe myofibromatosis. In conclusion, we identified gain-of-function PDGFRB mutations in the majority of multifocal infantile myofibromatosis cases, shedding light on the mechanism of disease development, which is reminiscent of multifocal venous malformations induced by TIE2 mutations. Our results provide a genetic test to facilitate diagnosis, and preclinical data for development of molecular therapies.