Chasing the ubiquitous RET proto-oncogene in South African MEN2 families – implications for the surgeon

Abstract

The RET proto-oncogene (REarranged during Transfection; RET) plays an important role in the causation of many thyroid tumours. Germline RET proto-oncogene missense mutations have been clearly linked to medullary thyroid carcinoma (MTC) and the inherited cancer syndrome multiple endocrine neoplasia type 2 (MEN2A, MEN2B). Methods. We investigated a cohort of MEN2-related patients referred to Tygerberg Hospital, W Cape (2003 - 2009). The study cohort was divided into three groups based on pathology (viz. MEN/MTC, phaeochromocytoma, and a called. Serum calcitonin levels were monitored where indicated. DNA was extracted from whole blood by standard techniques and polymerase chain reaction (PCR) products screened for RET gene variations by heteroduplex singlestrand duplication techniques (heteroduplex single-strand conformation polymorphism analysis) being validated with automated sequencing techniques showing conformational variants in acrylamide gel. Results. We screened 40 persons, male/female ratio 1:1.5. Three ethnic groups were represented (white (12), black (11) and mixed race (17)). Nine were index MTC cases, 5 phaeochromocytoma, 3 Hirschsprung’s disease- MEN associations and 2 miscellaneous (1 neuroblastoma, 1 intestinal neuronal dysplasia), while 1 fell into the MEN2B category. The remaining 19 were unaffected relatives screened for carrier status, among whom a familial recurrence was observed in 7. On genetic testing, an RET point mutation at the highrisk 634 cysteine allele was identified in 11 cases. A further cysteine radical mutation at the 620 position was related to MEN2 in 3 families plus 1 other family referred from elsewhere. Other less-recognised gene variations were detected throughout the RET gene in 70% of cases and included the 691 position on codon 11 (11 cases); the 432 position (4 cases, 1 homozygous) intronic mutations on exon 4 (1 case); and an IVS19-37G/C and a D1017N variation in exon 19 in 2 MEN families. Fifteen MTC patients have had thyroidectomies, of which 2 were prophylactic (C-cell hyperplasia; early occult MTC). A further 3 are awaiting prophylactic surgery. Conclusion. RET gene mutation carries a risk of MEN2 and MTC in all ethnic groups in South Africa. Prophylactic surgery may prevent MTC, so genetic screening is important to identify and treat high-risk patients.