Abstract Thyroid cancer is the 12th most common cancer in the USA. Four main types exist: the majority (85-90%) is papillary thyroid cancer (PTC). Familial form of PTC represents 5 to 15 % of all thyroid cancers. We have access to 155 PTC families including clinical data and biological samples. Our aim was to search for highly penetrant gene variants in 17 PTC families. Data from one of the families in which PTC is segregating in three generations are described here. Whole genome sequencing was performed in three family members affected by PTC. Sanger sequencing at germline DNA and RNA levels followed by TOPO cloning was used to study the effects of mutations. We found 4 different either novel or ultra-rare mutations in the ITGAD, AARS and PDPR genes on chromosome 16 (Table). All mutations segregated perfectly with PTC in family members (n=4) and were absent in unaffected members (n=3). We Sanger sequenced cDNA from two of the PTC patients and cloned the products into the pCR 2.1-® TOPO vector. Based on the cDNA sequencing and cloning results, all of the mutations will create a premature stop codon leading to a truncated protein. We will verify the effects of the mutations by protein analysis as well. In addition, structural variation analysis will be done to exclude large genomic rearrangements. The germline events leading to PTC are neither well known nor extensively researched. When occurring in families PTC regularly shows autosomal dominant inheritance with incomplete penetrance. Only a few of probable mutations have been reported. Nevertheless, our finding of the truncating mutations in 3 genes on chromosome 16 that are cosegregating with PTC in a 3-generation family is surprising. Even more so: is the localization of the three genes in one chromosome coincidental? Preliminary findings in some of the other 16 PTC families suggest that the occurrence of more than one truncating mutation is not a unique event. We look forward to answer the question whether combination of two or more mutant genes can be responsible for one disease segregating in families. Citation Format: Taina T. Nieminen, Daniel F. Comiskey, Yanqiang Wang, Sandya Liyanarachchi, Pamela Brock, Paivi Peltomaki, Huiling He, Albert de la Chapelle. Multiple rare germline variants in a thyroid cancer family [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4156.