Biallelic mutations in WRAP53 result in dysfunctional telomeres, Cajal bodies and DNA repair, thereby causing Hoyeraal-Hreidarsson syndrome

Approximately half of all cases of Hoyeraal-Hreidarsson syndrome (HHS), a multisystem disorder characterized by bone marrow failure, developmental defects and very short telomeres, are caused by germline mutations in genes related to telomere biology. However, the varying symptoms and severity of the disease indicate that additional mechanisms are involved. Here, a 3-year-old boy with HHS was found to carry biallelic germline mutations in WRAP53 (WD40 encoding RNA antisense to p53), that altered two highly conserved amino acids (L283F and R398W) in the WD40 scaffold domain of the protein encoded. WRAP53 beta (also known as TCAB1 or WDR79) is involved in intracellular trafficking of telomerase, Cajal body functions and DNA repair. We found that both mutations cause destabilization, mislocalization and faulty interactions of WRAP53 beta, defects linked to misfolding by the TRiC chaperonin complex. Consequently, WRAP53 beta HHS mutants cannot elongate telomeres, maintain Cajal bodies or repair DNA double-strand breaks. These findings provide a molecular explanation for the pathogenesis underlying WRAP53 beta-associated HHS and highlight the potential contribution of DNA damage and/or defects in Cajal bodies to the early onset and/or severity of this disease.