Submission Details

ZCCHC8 was first reported in relation to pulmonary fibrosis and/or bone marrow failure, telomere-related, 5 in 2019 (Gable DL et al., PMID:31488579). At least two missense variants have been reported in humans. Evidence supporting this gene-disease relationship includes case-level data, segregation data and experimental data.

Variants in this gene have been reported in at least 3 adult probands in 2 publications (PMIDs:31488579, 38375433). Variants in this gene segregated with disease in 11 additional family members. The individuals carrying these variants presented with pulmonary fibrosis with an adult onset and upon testing were found to have short telomeres. In addition, some of the individuals carrying the variant had bone marrow failure or hematologic disease.

This gene-disease relationship is supported by a mouse model, a cell culture model and immunofluorescent detection of ZCCHC8 in lung tissue (PMIDs: 38375433, 31488579). With transcriptomics and antibody-based proteomics Fagerberg L et al. showed that ZCCHC8 is highly expressed in the bone marrow as compared to other tissues. Groen K, et al. showed that ZCCHC8 is also expressed in alveolar type 2 cells, proSP-C negative cells in the alveoli, and CC10-positive cells in both healthy and affected patient tissues; these expression experiments show that the gene is expressed in the relevant tissues to pulmonary fibrosis and bone marrow failure (PMIDs:24309898, 38375433).

Gable DL et al. created a cell model where they disrupted the ZCCHC8 locus in HCT116 cells by using CRISPR/Cas9 to insert compound heterozygous frameshift mutations in HCT116 cells. The cell model showed both a reduction in telomerase activity and mature telomerase RNA (TR). Similarly, the authors show that knockdown of ZCCHC8 in HeLa cells via shRNA leads to decreased TR levels. In both the knockout cells and in the mutation carrier skin fibroblasts, there was an increase in immature forms of TR, with longer 3’-extensions beyond its mature end, consistent with a role of ZCCHC8 in mediating TR 3’-end processing in the nuclear RNA exosome. , demonstrating the human phenotype, which was confirmed with a control and lymphoblastoid cells from the proband. The same authors then rescued this phenotype, the accumulation of extended telomere RNA with the overexpression of ZCCHC8 in the cells (PMID:31488579).

Using CRISPR/Cas 9 genome editing, Gable DL et al. inserted 33-basepairs in exon 2 of the Zcchc8 gene to introduce a premature stop codon at amino acid 93. Heterozygous knockout mouse intercross breedings led to increased postnatal lethality of homozygous mice with a progressive and fatal neurodevelopmental defect. This is notable because one case exists in the literature of a proband from a consanguineous family carrying homozygous ZCCHC8 nonsense mutations with intellectual disability. This case was excluded from this curation because of the different inheritance pattern, the difference in clinical presentation, and limited phenotypic information (PMID:21937992). The knockout heterozygous and homozygous mice have less telomerase RNA (mTR). The amount of immature mTR is more striking in the homozygous mice, consistent with a dose-dependent role of ZCCHC8 in mediating 3’-end processing of the telomerase RNA.

In summary, there is moderate evidence to support this gene-disease relationship. While more evidence is needed to establish this relationship definitively, no convincing contradictory evidence has emerged. This classification was approved by the ClinGen Interstitial Lung Disease GCEP on the meeting date March 19, 2024 (SOP Version 10).