Genetic Variant Overlap Analysis Identifies Established and Putative Genes Involved in Pulmonary Fibrosis

Genetic Homogeneity of a TDP1 Variant, c.1478A>G, as the Main Disease-Causing Variant of Spinocerebellar Ataxia With Axonal Neuropathy 1 (SCAN1) in the Middle East: A Systematic Review

BACKGROUND

Spinocerebellar ataxia with axonal neuropathy 1 (SCAN1) is an ultrarare neurodegenerative disorder inherited in an autosomal recessive manner, mainly marked by progressive ataxia and axonal polyneuropathy. SCAN1 is mainly caused by the c.1478A>G:p.His493Arg mutation in the TDP1 gene. In this study, we present the first Iranian family, and the fifth family totally, diagnosed with the SCAN1, which carries the common variant c.1478A>G. Additionally, we conducted a systematic review to identify all reported probably disease-related variants of TDP1.

METHODS

Whole exome sequencing was performed on the proband, who was initially diagnosed with axonal neuropathy. The data were analyzed, and the variant was confirmed via Sanger sequencing. Cosegregation analysis was used to validate the variant within the family. Following PRISMA 2020 guidelines, we performed a systematic review using the terms TDP1, tyrosyl-DNA phosphodiesterase, SCAN1, and spinocerebellar ataxia with axonal neuropathy in four major databases.

RESULTS

Whole exome sequencing results identified the known TDP1:c.1478A>G variant, which correlated with the disease status in the family. Clinical and paraclinical findings were consistent with SCAN1. Our systematic review identified 16 variants in 20 families associated with various neurological or non-neurological disorders. Among these families, four were SCAN1. Although four of five families with SCAN1, including our family, shared the same TDP1 variant, c.1478A>G, they exhibited some clinical heterogeneity.

CONCLUSIONS

Given that all these cases were from the Middle East, we suggested this mutation may be a founder mutation in this region. Since only a few families with SCAN1 have been reported, further research is needed to fully understand this disorder.

Early Pulmonary Fibrosis-like Changes in the Setting of Heat Exposure: DNA Damage and Cell Senescence

It is well known that extreme heat events happen frequently due to climate change. However, studies examining the direct health impacts of increased temperature and heat waves are lacking. Previous reports revealed that heatstroke induced acute lung injury and pulmonary dysfunction. This study aimed to investigate whether heat exposure induced lung fibrosis and to explore the underlying mechanisms. Male C57BL/6 mice were exposed to an ambient temperature of 39.5 ± 0.5 °C until their core temperature reached the maximum or heat exhaustion state. Lung fibrosis was observed in the lungs of heat-exposed mice, with extensive collagen deposition and the elevated expression of fibrosis molecules, including transforming growth factor-β1 (TGF-β1) and Fibronectin (Fn1) (p < 0.05). Moreover, epithelial-mesenchymal transition (EMT) occurred in response to heat exposure, evidenced by E-cadherin, an epithelial marker, which was downregulated, whereas markers of EMT, such as connective tissue growth factor (CTGF) and the zinc finger transcriptional repressor protein Slug, were upregulated in the heat-exposed lung tissues of mice (p < 0.05). Subsequently, cell senescence examination revealed that the levels of both senescence-associated β-galactosidase (SA-β-gal) staining and the cell cycle protein kinase inhibitor p21 were significantly elevated (p < 0.05). Mechanistically, the cGAS-STING signaling pathway evoked by DNA damage was activated in response to heat exposure (p < 0.05). In summary, we reported a new finding that heat exposure contributed to the development of early pulmonary fibrosis-like changes through the DNA damage-activated cGAS-STING pathway followed by cellular senescence.

A new variant in the ZCCHC8 gene: diverse clinical phenotypes and expression in the lung

Introduction

Pulmonary fibrosis is a severe disease which can be familial. A genetic cause can only be found in ∼40% of families. Searching for shared novel genetic variants may aid the discovery of new genetic causes of disease.

Methods

Whole-exome sequencing was performed in 152 unrelated patients with a suspected genetic cause of pulmonary fibrosis from the St Antonius interstitial lung disease biobank. Variants of interest were selected by filtering for novel, potentially deleterious variants that were present in at least three unrelated pulmonary fibrosis patients.

Results

The novel c.586G>A p.(E196K) variant in the ZCCHC8 gene was observed in three unrelated patients: two familial patients and one sporadic patient, who was later genealogically linked to one of the families. The variant was identified in nine additional relatives with pulmonary fibrosis and other telomere-related phenotypes, such as pulmonary arterial venous malformations, emphysema, myelodysplastic syndrome, acute myeloid leukaemia and dyskeratosis congenita. One family showed incomplete segregation, with absence of the variant in one pulmonary fibrosis patient who carried a PARN variant. The majority of ZCCHC8 variant carriers showed short telomeres in blood. ZCCHC8 protein was located in different lung cell types, including alveolar type 2 (AT2) pneumocytes, the culprit cells in pulmonary fibrosis. AT2 cells showed telomere shortening and increased DNA damage, which was comparable to patients with sporadic pulmonary fibrosis and those with pulmonary fibrosis carrying a telomere-related gene variant, respectively.

Discussion

The ZCCHC8 c.586G>A variant confirms the involvement of ZCCHC8 in pulmonary fibrosis and short-telomere syndromes and underlines the importance of including the ZCCHC8 gene in diagnostic gene panels for these diseases.