WRN and Bloom syndrome: The occurrence of OS has been associated with several rare cancer predisposition syndromes including Li–Fraumeni syndrome (mutations of the TP53 gene), hereditary retinoblastoma (mutations of the RB1 gene), Bloom syndrome (mutations of the RECQL3 gene), Werner syndrome (mutations of the RECQL2 (WRN) gene), and Rothmund–Thomson-syndromes (mutations of the RECQL4 gene)5.