A 4-Year-Old Boy with an Accidentally Detected Mutation in the RET Proto-Oncogene and Mutation in the Gene Encoding the Ryanodine Receptor1 (RyR1)-Case Report.

Multiple endocrine neoplasia 2B (MEN2B) is a rare syndrome with prevalence estimated at approximately 0.2 per 100,000; it is caused by mutation of the RET proto-oncogene. MEN2B is characterized by early-onset medullary thyroid carcinoma (MTC), ganglioneuromatosis of the aerodigestive tract, marfanoid habitus, ophthalmologic abnormalities, and pheochromocytoma in adulthood. Mutations in the RyR1 gene manifest clinically in congenital myopathies and/or malignant hyperthermia susceptibility. We present a case of a 4-year-old boy with an accidentally detected RET and RyR1 mutations in the course of diagnostic approach of short stature and delayed motor development. Due to a poor and blurred clinical picture of MEN2B syndrome, accompanied by RyR1 mutation symptoms, the diagnostic path was extended. Our patient had no family history of MTC. In the imaging studies of the thyroid gland, no abnormalities were found, whereas the serum level of calcitonin was elevated to 34 pg/mL (N < 5.0). The patient qualified for total thyroidectomy, and the histopathological examination confirmed the diagnosis of MTC. The postoperative serum calcitonin level dropped to normal ranges. This case shows how new genetic diagnostic procedures could be crucial in accidentally diagnosing rare endocrine disease with atypical symptoms, giving an opportunity for relatively early intervention.