[Pulmonary fibrosis associated with hereditary fibrosing poikiloderma caused by FAM111B mutation: A case report]

Loss of FAM111B protease mutated in hereditary fibrosing poikiloderma negatively regulates telomere length

Hereditary fibrosing poikiloderma (HFP) is a rare human dominant negative disorder caused by mutations in the FAM111B gene that encodes a nuclear trypsin-like serine protease. HFP patients present with symptoms including skin abnormalities, tendon contractures, myopathy and lung fibrosis. We characterized the cellular roles of human FAM111B using U2OS and MCF7 cell lines and report here that the protease interacts with components of the nuclear pore complex. Loss of FAM111B expression resulted in abnormal nuclear shape and reduced telomeric DNA content suggesting that FAM111B protease is required for normal telomere length; we show that this function is independent of telomerase or recombination driven telomere extension. Even though FAM111B-deficient cells were proficient in DNA repair, they showed hallmarks of genomic instability such as increased levels of micronuclei and ultra-fine DNA bridges. When mutated as in HFP, FAM111B was more frequently localized to the nuclear envelope, suggesting that accumulation of the mutated protease at the nuclear periphery may drive the disease pathology.

Case report: Discovery of a de novo FAM111B pathogenic variant in a patient with an APECED-like clinical phenotype

Introduction

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) and poikiloderma in association with tendon contractures, myopathy, and pulmonary fibrosis (POIKTMP) are rare inherited syndromes resulting from biallelic pathogenic variants in AIRE and heterozygous pathogenic variants in FAM111B, respectively. The clinical diagnosis of APECED and POIKTMP rely on the development of two or more characteristic disease manifestations that define the corresponding syndromes. We discuss the shared and distinct clinical, radiographic, and histological features between APECED and POIKTMP presented in our patient case and describe his treatment response to azathioprine for POIKTMP-associated hepatitis, myositis, and pneumonitis.

Methods

Through informed consent and enrollment onto IRB-approved protocols (NCT01386437, NCT03206099) the patient underwent a comprehensive clinical evaluation at the NIH Clinical Center alongside exome sequencing, copy number variation analysis, autoantibody surveys, peripheral blood immunophenotyping, and salivary cytokine analyses.

Results

We report the presentation and evaluation of a 9-year-old boy who was referred to the NIH Clinical Center with an APECED-like clinical phenotype that included the classic APECED dyad of CMC and hypoparathyroidism. He was found to meet clinical diagnostic criteria for POIKTMP featuring poikiloderma, tendon contractures, myopathy, and pneumonitis, and exome sequencing revealed a de novo c.1292T>C heterozygous pathogenic variant in FAM111B but no deleterious single nucleotide variants or copy number variants in AIRE.

Discussion

This report expands upon the available genetic, clinical, autoantibody, immunological, and treatment response information on POIKTMP.

Hereditary fibrosing poikiloderma (POIKTMP syndrome) report of a new mutation and review of the literature

Hereditary fibrosing poikiloderma with tendon contractures, myopathy, and pulmonary fibrosis (POIKTMP) is a genodermatosis with autosomal dominant inheritance caused by mutations in FAM111B. We report another case with a new pathogenic variant and analyze all previously published 34 cases with a focus on sequence of clinical presentation and genotype-phenotype correlation. POIKTMP is characterized by marked age-dependent clinical expressivity. FAM111B encodes a catalytic nuclear protein, expressed in many tissues, which contributes to impaired DNA repair affecting multiple systems. Specific inhibition of catalytic activity might be a future strategy to halt progression of this otherwise untreatable disease. Given the relentless progression of the disease, it would make sense to start such treatment as early as possible. In order to achieve this objective, children with suspected POIKTMP should therefore undergo early imaging of all relevant organ systems.

FAM111B dysregulation promotes malignancy in fibrosarcoma and POIKTMP and a low-cost method for its mutation screening

INTRODUCTION

Mutations in the uncharacterised human FAM111B gene are associated with POIKTMP, a rare multi-organ fibrosing disease. Recent studies also reported the overexpression of FAM111B in specific cancers. Moreover, FAM111B mutation screening may prove expensive in under-resourced facilities. Therefore, this study investigated its cellular function and dysfunction and described an inexpensive mutation screening method.

MATERIALS AND METHODS

FAM111B expression was assessed in silico and validated in vitro in cell lines and primary skin fibroblasts from a South African POIKTMP-patient with the heterozygous FAM111B gene mutation: NM_198947.4: c.1861T>G (p. Tyr621Asp or Y621D) by qPCR and western blot. The cellular function of FAM111B was studied in HT1080 using various cell-based functional assays, and the Y621D mutation was genotyped by PCR-RFLP.

RESULTS

Expression studies showed upregulated FAM111B mRNA and protein in the cancer cells. High FAM111B expression with robust nuclear localization occurred in HT1080. Additionally, expression data and cell-based assays indicated that FAM111B led to the upregulation of cell migration, decreased cell apoptosis, and modulatory effects on cell proliferation. Y621D mutation showed similar effects on cell migration but minimal impact on cell apoptosis. FAM111B mRNA and protein expression were markedly downregulated (p ≤ 0.05) in the POIKTMP-patient's fibroblasts. The PCR-RFLP method successfully genotyped Y621D gene mutation.

DISCUSSION

FAM111B is a cancer-associated nuclear protein: Its modulation by mutations or overexpression may contribute to the malignancy of cancers and POIKTMP/fibrosis and poor clinical outcomes and represents a viable prognostic marker or therapeutic target. Furthermore, the PCR-RFLP method could prove a valuable tool for FAM111B mutation validation or screening in resource-constrained laboratories.

Proposed Cellular Function of the Human FAM111B Protein and Dysregulation in Fibrosis and Cancer

FAM111B gene mutations are associated with a hereditary fibrosing poikiloderma known to cause poikiloderma, tendon contracture, myopathy, and pulmonary fibrosis (POIKTMP). In addition, the overexpression of FAM111B has been associated with cancer progression and poor prognosis. This review inferred the molecular function of this gene's protein product and mutational dysfunction in fibrosis and cancer based on recent findings from studies on this gene. In conclusion, FAM111B represents an uncharacterized protease involved in DNA repair, cell cycle regulation, and apoptosis. The dysregulation of this protein ultimately leads to fibrotic diseases like POIKTMP and cancers via the disruption of these cellular processes by the mutation of the FAM111B gene. Hence, it should be studied in the context of these diseases as a possible therapeutic target.

Case Report: Hereditary Fibrosing Poikiloderma With Tendon Contractures, Myopathy, and Pulmonary Fibrosis (POIKTMP) Presenting With Liver Cirrhosis and Steroid-Responsive Interstitial Pneumonia

Background: Hereditary fibrosing poikiloderma with tendon contractures, myopathy, and pulmonary fibrosis (POIKTMP) is an extremely rare disease caused by mutations in FAM111B, and only approximately 30 cases have been reported worldwide. Some patients develop interstitial pneumonia, which may lead to progressive pulmonary fibrosis and poor prognosis. However, no effective treatment for interstitial pneumonia associated with POIKTMP has been reported. Here, we report an autopsy case of POIKTMP, wherein interstitial pneumonia was improved by corticosteroids. Case Presentation: A 44-year-old Japanese man was referred to our hospital due to poikiloderma, hypotrichosis, and interstitial pneumonia. He developed progressive poikiloderma and muscle weakness since infancy. He also had tendon contractures, short stature, liver cirrhosis, and interstitial pneumonia. Mutation analysis of FAM111B revealed a novel and de novo heterozygous missense mutation, c.1886T > G (p(Phe629Cys)), through which we were able to diagnose the patient with POIKTMP. 3 years after the POIKTMP diagnosis, interstitial pneumonia had worsened. After 2 weeks of administrating 40 mg/day of prednisolone, his symptoms and lung shadows improved. However, he subsequently developed severe hepatic encephalopathy and eventually died of respiratory failure due to bacterial pneumonia and pulmonary edema. Autopsy revealed an unclassifiable pattern of interstitial pneumonia, as well as the presence of fibrosis and fatty degeneration in several organs, including the liver, kidney, skeletal muscle, heart, pancreas, and thyroid. Conclusions: We report a case of POIKTMP in which interstitial pneumonia was improved by corticosteroids, suggesting that corticosteroids could be an option for the treatment of interstitial pneumonia associated with this disease.

Spontaneous chromosomal instability in peripheral blood lymphocytes from two molecularly confirmed Italian patients with Hereditary Fibrosis Poikiloderma: insights into cancer predisposition

Two Italian patients with the initial clinical diagnosis of Rothmund-Thomson syndrome were negative for RECQL4 mutations but showed in peripheral blood cells a spontaneous chromosomal instability significantly higher than controls. Revisiting after time their clinical phenotype, the suggestive matching with the autosomal dominant syndrome Poikiloderma, Hereditary Fibrosing with Tendon Contracture, Myopathy and Pulmonary fibrosis (POIKTMP) was confirmed by identification of the c.1879A>G (p.Arg627Gly) alteration in FAM111B. We compare the overall clinical signs of our patients with those of reported carriers of the same mutation and present the up-to-date mutational repertoire of FAM111B and the related phenotypic spectrum. Our snapshot highlights the age-dependent clinical expressivity of POIKTMP and the need to follow-up patients to monitor the multi-tissue impairment caused by FAM111B alterations. We link our chromosomal instability data to the role of FAM111B in cancer predisposition, pointed out by its implication in DNA-repair pathways and the outcome of pancreatic cancer in 2 out of 17 adult POIKTMP patients. The chromosomal instability herein highlighted well connects POIKTMP to cancer-predisposing syndromes, such as Rothmund-Thomson which represents the first hereditary poikiloderma entering in differential diagnosis with POIKTMP.