Abstract

Background Dyskeratosis congenita (DC; OMIM: 127550) is a rare inherited bone marrow failure syndrome. TINF2 mutations are the second most common genetic cause of DC, and most cases arise from de novo mutations. Although the TINF2 p.Thr284Pro variant has been reported in isolated cases, its pathogenic role has not been functionally validated, and its potential association with suspected parental gonadal/gonadosomatic mosaicism has not been previously described. Objective To evaluate the functional impact of the TINF2 p.Thr284Pro variant and explore its association with suspected parental gonadal/gonadosomatic mosaicism in a DC pedigree in which two affected sisters were born to clinically unaffected parents. The findings may provide evidence for improved molecular diagnosis and genetic counseling in DC. Methods Clinical and genetic investigations were performed in a family suspected of DC. Multi-tissue sequencing was conducted in the parents and the proband. To evaluate the functional consequences of the variant, wild-type and p.Thr284Pro mutant TINF2 overexpression plasmids were constructed and transfected into HEK293T cells. TINF2 protein expression was analyzed by Western blotting. Cell proliferation was assessed using the CCK-8 assay, telomere length was measured by quantitative PCR, and cellular senescence was evaluated using SA-β-galactosidase staining. Results Both affected sisters exhibited an incomplete classical DC phenotype, characterized primarily by pancytopenia and nail dystrophy. Genetic analysis identified the same heterozygous TINF2 c.850A>C (p.Thr284Pro) variant in both patients. This variant was absent in peripheral blood and other parental tissues (oral mucosa and hair follicles), suggesting an apparently de novo occurrence in the siblings and raising the possibility of suspected parental gonadal/gonadosomatic mosaicism. Functional assays provided preliminary supportive evidence that the mutant construct was associated with low