Penetrance and Clinical Features of Pheochromocytoma in a Six-Generation Family Carrying a Germline TMEM127 Mutation

Context: The phenotype of familial pheochromocytoma (PHEO) associated with germline TMEM127 mutations (TMEM127-related PHEO) has not been clearly defined. Objective: This study aimed to investigate the penetrance, full phenotypic spectrum and effectiveness of clinical/genetic screening in TMEM127-related PHEO. Design, Setting, and Participants: Clinical and genetic screening, and genetic counseling were offered to 151 individuals from a six-generation family carrying a TMEM127 germline mutation in a referral center. Intervention and Main Outcome Measures: TMEM127 genetic testing was offered to at-risk relatives and clinical surveillance for pheochromocytoma was performed in mutation-positive carriers. Results: Forty seven individuals carried the c.410-2A>C TMEM127 mutation. Clinical data were obtained from 34 TMEM127-mutation carriers followed up for 8.7 +/- 8.1 years (range, 1-20 y). Pheochromocytoma was diagnosed in 11 carriers (32%) at a median age of 43 years. In nine patients, symptoms started at 29 years (range, 10-55 y) and two cases were asymptomatic. Tumors were multicentric in five (45%) and bilateral in five (45%) patients. Six patients (54%) had at least one adrenomedullary nodule less than 10 mm. No paragangliomas, distant metastases, or other manifestations were detected. Cumulative penetrance of pheochromocytoma was 0% at 0-20 years, 3% at 21-30 years, 15% at 31-40 years, 24% at 41-50 years, and 32% at 51-65 years. The youngest case was diagnosed at 22 years and the earliest symptoms were reported at age 10. Conclusions: Tumor multicentricity, nodular adrenomedullary hyperplasia, and the occurrence of symptoms more than a decade earlier than the age at diagnosis are novel findings in TMEM127-related PHEO. The high penetrance of pheochromocytoma in this condition validates the benefits of genetic testing of at-risk relatives. We thus recommend that TMEM127 genetic testing should be offered to at-risk individuals at age 22 years and mutation carriers should undergo clinical surveillance annually.