Head And Neck Paraganglioma Patients With Succinate Dehydrogenase Gene Pathogenic Mutations

Paragangliomas are rare tumors occurring at head and neck area. Recently, it has been revealed that paragangliomas have a relationship with germline mutations of succinate dehydrogenase encoding genes. To evaluate the role and characteristics of SDH gene mutations in Chinese patients, we collected DNA samples of familiar and sporadic patients with head and neck paraganliomas and screened for germline mutations. We also analyzed the pathogenicity of the mutations and genotyped the haplotypes of the patients with same mutations.The study consists of 4 portions:Part 1:Collection of clinical data and DNA samples of HNPGL patientsWe recalled the case records on PGL and select the HNPGL cases confirmed by pathologic diagnosis. We contacted the patients and informed them about our study. With their consents, we registered their detailed clinical and familiar information and we collected blood samples from every patient and the formalin-fixed and paraffin-embedded (FFPE) tissue samples from the department of Pathology. In total,34 blood samples and 83 FFPE tissue samples (including the 34 patients with available blood samples) were collected. DNA was extracted from 34 blood samples (9 males and 25 females) and 30 FFPE tissue samples (13 males and 17 females). Part 2:Genetic assay of SDH genes for point mutations.We designed primers for all of the SDHB, SDHC and SDHD exons according to our requirements. Genetic assays were done for 64 HNPGL patients. Each exon of SDH genes was amplified and direct sequenced. By sequence BLASTing, we revealed that 48.5% of the 64 patients carry SDH mutations (10 SDHB mutations,3 SDHC mutations and 18 SDHD mutations) and 9 novel mutations were identified.Part 3:Large deletion detection for SDH genesFor the 33 patients without any mutation of SDH genes, we detect the large deleton of SDH genes by multiplex ligation-dependent probe amplification. None of these patient was revealed to carry a SDH gene copy number variant.Part 4:Haplotype analysis of patients with a same mutationThree chinese patients were reported to carry the SDHD c.3G>C mutation and another 2 patients with this mutation were identified in our study. We constructed the haplotype for 4 of the 5 families and compared the STR combinations between the families. We also calculated the probabilities of the STR combinations shared by these families in a control group of 75 blood donors and the result showed that the same mutation shared by these families are due to a founder effect.Conclusion:There are 48.5% of the 64 patients carrying SDH mutations, including 10 SDHB mutations,3 SDHC mutations and 18 SDHD mutations. Nine novel mutations were identified. None was found to carry a SDHAF2 gene mutation or copy number variant. SDHD c.3G>C mutation is due to a founder effect.