Familial medullary thyroid carcinoma and prominent corneal nerves associated with the germline V804M and V778I mutations on the same allele of RET

Editor—Germline mutations in the RET proto-oncogene are associated with multiple endocrine neoplasia (MEN) type 2A, 2B, and familial medullary thyroid carcinoma (FMTC). MEN 2A is characterised primarily by medullary thyroid carcinoma (MTC), parathyroid hyperplasia, and phaeochromocytoma. MEN 2B has additional stigmata including a marfanoid habitus, mucosal neuromas, and corneal nerve thickening. In FMTC, the only lesion present is MTC. Although characteristic of MEN 2B, prominent corneal nerves have been noted in subjects with MEN 2A. We have studied a family presenting with MTC and corneal nerve thickening (CNT), but no evidence of MEN 2 related disease outside the thyroid gland (fig 1). The proband (III.1) was found to have prominent corneal nerves on routine ophthalmological examination in his late 30s. No further action was taken and he presented with a palpable thyroid mass at the age of 53. Figure 1 A truncated pedigree of the family is shown. Filled symbols indicate affected subjects. The letters below the symbols refer to the site of cancer, the numbers following the abbreviations indicate age at diagnosis. MTC, medullary thyroid cancer; PSU, primary site unknown; d, age at death; CNT, corneal nerve thickening. MEN 2B was suspected and he was referred for laboratory screening tests for MTC and phaeochromocytoma. Serum calcitonin was raised at 4090 ng/l (normal range <60 ng/l). Serum calcium and phosphorus were normal. Twenty four hour urinary total catecholamine, metanephrine, and vanillylmandelic acid levels were within normal limits. A thoracic and abdominal CT scan performed before surgery was normal and scanning of the neck confirmed the presence of the right thyroid mass. The patient underwent a total thyroidectomy and pathological examination indicated bilateral MTC with extension beyond the capsule. His endocrinologist referred him for a genetic evaluation with a diagnosis of MEN 2B. However, other than CNT, he and his relatives …