Pulmonary non-tuberculous mycobacterial infection in congenital contractural arachnodactyly

A patient with pleuroparenchymal fibroelastosis carrying a novel fibrillin-2 gene variant

Pleuroparenchymal fibroelastosis is a recently recognized clinical entity characterized by interstitial pneumonia with proliferating elastin in the upper lung regions. Pleuroparenchymal fibroelastosis is categorized as idiopathic or reported depending on the coexistent initiating factors; however, congenital contractural arachnodactyly, which is caused by abnormal production of elastin based on a mutation in the fibrillin-2 gene, is rarely reported with lung lesion resembling pleuroparenchymal fibroelastosis. We present a case of pleuroparenchymal fibroelastosis in a patient with a novel mutation in the fibrillin-2 gene, which encodes the prenatal fibrillin-2 protein as a scaffold for elastin.

Mycobacterium abscessus: It’s Complex

Mycobacterium abscessus (M. abscessus) is an opportunistic pathogen usually colonizing abnormal lung airways and is often seen in patients with cystic fibrosis. Currently, there is no vaccine available for M. abscessus in clinical development. The treatment of M. abscessus-related pulmonary diseases is peculiar due to intrinsic resistance to several commonly used antibiotics. The development of either prophylactic or therapeutic interventions for M. abscessus pulmonary infections is hindered by the absence of an adequate experimental animal model. In this review, we outline the critical elements related to M. abscessus virulence mechanisms, host–pathogen interactions, and treatment challenges associated with M. abscessus pulmonary infections. The challenges of effectively combating this pathogen include developing appropriate preclinical animal models of infection, developing proper diagnostics, and designing novel strategies for treating drug-resistant M. abscessus.

Adding Another Piece to the Puzzle of Why NTM Infections Are Relatively Uncommon despite Their Ubiquitous Nature

Since nontuberculous mycobacteria (NTM) are pervasive in the environment and NTM infections are relatively uncommon, underlying hereditary or acquired host susceptibility factors should be sought for in most NTM-infected patients. To facilitate identification of underlying risk factors, it is useful to classify NTM disease into skin-soft tissue infections, isolated NTM lung disease, and extrapulmonary viscera-disseminated disease because the latter two categories have unique sets of underlying host risk factors.

Since nontuberculous mycobacteria (NTM) are pervasive in the environment and NTM infections are relatively uncommon, underlying hereditary or acquired host susceptibility factors should be sought for in most NTM-infected patients. To facilitate identification of underlying risk factors, it is useful to classify NTM disease into skin-soft tissue infections, isolated NTM lung disease, and extrapulmonary visceral/disseminated disease because the latter two categories have unique sets of underlying host risk factors. Nakajima and coworkers (M. Nakajima, M. Matsuyama, M. Kawaguchi, T. Kiwamoto, et al., mBio 12:e01947-20, 2021, https://doi.org/10.1128/mBio.01947-20) in a recent issue of mBio found that Nrf2 (nuclear factor erythroid 2-related factor 2), a transcription factor that is induced by oxidative stress but induces antioxidant molecules, provides protection against an NTM infection in a murine model. While they showed that Nrf2 induction of Nramp-1 enhanced phagosome-lysosome fusion, we discuss other potential mechanisms by which oxidative stress predisposes to and Nrf2 protects against NTM infections.

Enlarged Dural Sac in Idiopathic Bronchiectasis Implicates Heritable Connective Tissue Gene Variants

RATIONALE

Patients with idiopathic bronchiectasis are predominantly female and have an asthenic body morphotype and frequent nontuberculous mycobacterial respiratory infections. They also demonstrate phenotypic features (scoliosis, pectus deformity, mitral valve prolapse) that are commonly seen in individuals with heritable connective tissue disorders.

OBJECTIVES

To determine whether lumbar dural sac size is increased in patients with idiopathic bronchiectasis as compared with control subjects, and to assess whether dural sac size is correlated with phenotypic characteristics seen in individuals with heritable connective tissue disorders.

METHODS

Two readers blinded to diagnosis measured anterior-posterior and transverse dural sac diameter using L1-L5 magnetic resonance images of 71 patients with idiopathic bronchiectasis, 72 control subjects without lung disease, 29 patients with cystic fibrosis, and 24 patients with Marfan syndrome. We compared groups by pairwise analysis of means, using Tukey's method to adjust for multiple comparisons. Dural sac diameter association with phenotypic and clinical features was also tested.

MEASUREMENTS AND MAIN RESULTS

The L1-L5 (average) anterior-posterior dural sac diameter of the idiopathic bronchiectasis group was larger than those of the control group (P < 0.001) and the cystic fibrosis group (P = 0.002). There was a strong correlation between increased dural sac size and the presence of pulmonary nontuberculous mycobacterial infection (P = 0.007) and long fingers (P = 0.003). A trend toward larger dural sac diameter was seen in those with scoliosis (P = 0.130) and those with a family history of idiopathic bronchiectasis (P = 0.149).

CONCLUSIONS

Individuals with idiopathic bronchiectasis have an enlarged dural sac diameter, which is associated with pulmonary nontuberculous mycobacterial infection, long fingers, and family history of idiopathic bronchiectasis. These findings support our hypothesis that "idiopathic" bronchiectasis development reflects complex genetic variation in heritable connective tissue and associated transforming growth factor-β-related pathway genes.

Whole exome sequencing identifies a novel missense FBN2 mutation co-segregating in a four-generation Chinese family with congenital contractural arachnodactyly

BACKGROUND

Congenital contractural arachnodactyly (CCA) is an autosomal dominant rare genetic disease, estimated to be less than 1 in 10,000 worldwide. People with this condition often have permanently bent joints (contractures), like bent fingers and toes (camptodactyly).

CASE PRESENTATION

In this study, we investigated the genetic aetiology of CCA in a four-generation Chinese family. The blood samples were collected from 22 living members of the family in the Yangquan County, Shanxi Province, China. Of those, eight individuals across 3 generations have CCA. Whole exome sequencing (WES) identified a missense mutation involving a T-to-G transition at position 3229 (c.3229 T > G) in exon 25 of the FBN2 gene, resulting in a Cys 1077 to Gly change (p.C1077G). This previously unreported mutation was found in all 8 affected individuals, but absent in 14 unaffected family members. SIFT/PolyPhen prediction and protein conservation analysis suggest that this novel mutation is pathogenic. Our study extended causative mutation spectrum of FBN2 gene in CCA patients.

CONCLUSIONS

This study has identified a novel missense mutation in FBN2 gene (p.C1077G) resulting in CCA in a family of China.

A novel FBN2 mutation in a Chinese family with congenital contractural arachnodactyly

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We identified a novel FBN2 mutation (C1406R) in a Chinese family with CCA.

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The mutation presented in the patients of this family but not in unaffected members.

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SIFT and PolyPhen analyses suggested that the mutation was pathogenic.

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The mutation was located in the calcium-binding epidermal growth factor-like domain.

Congenital contractural arachnodactyly (CCA, OMIM: 121050) is an autosomal dominant condition that shares skeletal features with Marfan syndrome (MFS, OMIM: 154700), including contractures, arachnodactyly, dolichostenomelia, scoliosis, crumpled ears and pectus deformities but excluding the ocular and cardiovascular complications that characterize MFS. These two similar syndromes result from mutations in two genes belonging to the fibrillin family, FBN1 and FBN2, respectively. We successfully identified a novel FBN2 mutation (C1406R) in a Chinese family with CCA for over five generations. This mutation was detected in the patients of this family but not in the seven unaffected family members or 100 normal individuals. SIFT and PolyPhen analyses suggested that the mutation was pathogenic. We identified a missense mutation in the calcium binding-epidermal growth factor (cbEGF)-like domain. Our study extends the mutation spectrum of CCA and confirms a relationship between mutations in the FBN2 gene and the clinical findings of CCA.

Pathogenesis and risk factors for nontuberculous mycobacterial lung disease

Nontuberculous mycobacteria (NTM) infections are broadly classified as skin and soft tissue infections, isolated lung disease, and visceral or disseminated disease. The degree of underlying immune abnormalities varies between each classification. Skin and soft tissue infections are usually the result of iatrogenic or accidental inoculation of NTM in otherwise normal hosts. Visceral and disseminated NTM disease invariably occurs in individuals with more severe immunosuppression. Although the focus of this article is to discuss the pathogenesis of NTM lung disease, the risk factors of visceral/disseminated NTM disease are also summarized, as they provide insights into host-defense mechanisms against these organisms.

Patients with nontuberculous mycobacterial lung disease exhibit unique body and immune phenotypes

RATIONALE

Among patients with nontuberculous mycobacterial lung disease is a subset of previously healthy women with a slender body morphotype, often with scoliosis and/or pectus excavatum. We hypothesize that unidentified factors predispose these individuals to pulmonary nontuberculous mycobacterial disease.

OBJECTIVES

To compare body morphotype, serum adipokine levels, and whole-blood cytokine responses of patients with pulmonary nontuberculous mycobacteria (pNTM) with contemporary control subjects who are well matched demographically.

METHODS

We enrolled 103 patients with pNTM and 101 uninfected control subjects of similar demographics. Body mass index and body fat were quantified. All patients with pNTM and a subset of control subjects were evaluated for scoliosis and pectus excavatum. Serum leptin and adiponectin were measured. Specific cytokines important to host-defense against mycobacteria were measured in whole blood before and after stimulation.

MEASUREMENTS AND MAIN RESULTS

Patients with pNTM and control subjects were well matched for age, gender, and race. Patients with pNTM had significantly lower body mass index and body fat and were significantly taller than control subjects. Scoliosis and pectus excavatum were significantly more prevalent in patients with pNTM. The normal relationships between the adipokines and body fat were lost in the patients with pNTM, a novel finding. IFN-γ and IL-10 levels were significantly suppressed in stimulated whole blood of patients with pNTM.

CONCLUSIONS

This is the first study to comprehensively compare body morphotype, adipokines, and cytokine responses between patients with NTM lung disease and demographically matched controls. Our findings suggest a novel, predisposing immunophenotype that should be mechanistically defined.