Multiple endocrine neoplasia type 2 (MEN2) is a rare, autosomal dominant endocrine disease. Currently, the RET proto-oncogene is the only gene implicated in MEN2A pathogenesis. Once an RET carrier is detected, family members should be screened to enable early detection of medullary thyroid carcinoma, pheochromocytoma, and hyperparatitity. Among these, medullary thyroid carcinoma is the main factor responsible for patient mortality. Accordingly, delineating strategies to inform clinical follow-up and treatment plans based on genes is paramount for clinical practitioners.

Herein, we present RET proto-oncogene mutations, clinical characteristics, and treatment strategies in a family with MEN2A. A family study was conducted on patients diagnosed with MEN2A. DNA was extracted from the peripheral blood of family members, and first-generation exon sequencing of the RET proto-oncogene was conducted. The C634Y mutation was identified in three family members spanning three generations. Two patients were sequentially diagnosed with pheochromocytomas and bilateral medullary thyroid carcinomas. A 9-year-old child harboring the gene mutation was diagnosed with medullary thyroid carcinoma. Surgical resection of the tumors was performed. All family members were advised to undergo complete genetic testing related to the C634Y mutation, and the corresponding treatments administered based on test results and associated clinical guidelines.

Advancements in MEN2A research are important for familial management, assessment of medullary thyroid cancer invasive risk, and deciding surgical timing.

Multiple endocrine neoplasia type 2 (MEN2) is a rare, autosomal dominant endocrine disease. It has two distinct subtypes, MEN2A (95%) and MEN2B (5%)[1,2], with an incidence rate of MEN2A 13–24 per 1000000[1,2]. Currently, the RET proto-oncogene is the only gene implicated in the pathogenesis of MEN2A. With a clear correlation between the genotype and phenotype, the RET proto-oncogene serves as an essential diagnostic tool for MEN2A. Managing patients through RET proto-oncogene testing and genetic counseling can not only optimize the prognosis associated with the genotype but also improve the quality of life of the patient's family members.

In this study, we retrospectively analyzed the clinical characteristics and gene mutation status of three generations of a Han Chinese family diagnosed with MEN2A to explore the significance of RET mutations and their relevance for clinical diagnosis and treatment and determine their pathological characteristics.

Three family members were diagnosed with MEN2 and harbored a c.T1901A mutation in the 11^th exon of RET.

The patient underwent thyroidectomy and was diagnosed with medullary thyroid carcinoma by postoperative pathology.

The patient's father and his son, who was found to harbor a mutation in the RET proto-oncogene, underwent adrenal and thyroid screening. The father was diagnosed with bilateral pheochromocytoma and medullary thyroid carcinoma with metastasis, while the son was diagnosed with medullary thyroid carcinoma.

There is a strong correlation between the incidence and prognosis of MEN2A and mutations in the RET proto-oncogene. Donis-Keller et al[3] were the first to report that mutations in the RET proto-oncogene cause MEN2A. Three years later, the International RET Mutation Consortium compiled and investigated the clinical and pathological characteristics of RET proto-oncogenes in 477 families with MEN2A, MEN2B, and familial medullary thyroid cancer (FMTC) mutations, confirming the pathogenic role of the RET proto-oncogene in MEN2 syndrome. Located on 10q11.2, the RET proto-oncogene, a tyrosine kinase receptor, comprises 21 exons and approximately 1100 amino acid residues. When RET receptors dimerize after binding to the co-receptor (GDNF family receptor alpha), the phosphorylation of intracellular tyrosine residues is triggered, thus playing a role in cell proliferation regulation, cell differentiation, gene expression, and other cellular processes. This cascade can lead to excessive cell proliferation, resulting in carcinogenesis.

To date, over 1000 cases of MEN2A, both sporadic and familial, have been reported globally, with less than 200 cases reported in China, including more than 80 sporadic and 90 familial cases[4-6]. Approximately 95% of patients with classic MEN2A harbor RET gene mutations at codons 634, 609, 611, and 618 of exon 11 and codon 620 of exon 10; of these, 85% are located in codon 634 of exon 11[7]. In a comprehensive global review on MEN2-related RET pathogenic variants, the pathogenic variants at codon 634 are the most prevalent, found in between 30% and 50% of affected patients; for codon 634 mutations, the relative frequency in China is higher than those found in Brazil, France, Germany, Italy, United Kingdom, Japan, or United States[8].

There are four MEN2A variants: Classic MEN2A, MEN2A with cutaneous lichen amyloidosis, MEN2A with Hirschsprung disease, and MEN2A with FMTC[1,2]. Classic MEN2A is the most common type, manifesting primarily as medullary thyroid cancer (MTC), pheochromocytoma, and hyperparathyroidism[7]. Nearly 100% of patients present with multifocal and bilateral MTC, which is typically the first disorder, usually occurring before 30 years of age[9]. Only 15% of MEN2A cases are symptomatic at the time of diagnosis, and the remaining 85% are identified via screening[10].

The occurrence of MEN2A associated with extra-adrenal and malignant pheochromocytomas[11] is rare. Primary hyperparathyroidism may not be prevalent in MEN2A, potentially appearing in as few as 3%-11% of cases[12]. Most cases (56%-88%) are asymptomatic at the time of diagnosis[13], and complications, such as hypercalcemia crisis, are rare. RET gene testing is especially crucial for early MEN2A detection, offering predictive diagnosis and treatment for family members.

Mortality in MEN 2 is primarily attributed to MTC. The 10-year overall survival for patients with MTC has been estimated to be 64%[14]. Guidelines from the American, British, and European Thyroid Associations endorse RET analysis for all patients with confirmed MTC. Over 50% of patients with MTC with lymph node involvement experience disease relapse leading to death, which is the primary cause of mortality in patients with MEN2A[15]. A large long-term follow-up study demonstrated that prophylactic thyroidectomy in patients with MEN2A harboring the C634Y mutation enables disease cure without inducing any long-term complications[16]. Therefore, the prognosis of MEN2A primarily depends on the status of MTC. Currently, surgery is the only effective treatment for MTC. Prophylactic thyroidectomy in patients with early asymptomatic MEN2A is crucial to prevent carcinogenesis and its complications and improve survival rates.

When considering prophylactic thyroidectomy, the focus is on the RET mutation type, age, and calcitonin level. The American Thyroid Association classifies RET mutations into three categories based on the invasive risk of MTC: Medium, high, and extremely high. The more invasive the tumor, the earlier the prophylactic thyroidectomy should be performed and the larger the range of the thyroid necessitating surgical removal. Based on this categorization, different surgical indications have been proposed for patient treatment depending on the risk level[7,17]. The classic MEN2A 634 chromosomal mutation is a high-risk mutation; high-risk mutations transition from normal to C-cell hyperplasia within an average of 5 years, and to MTC N0 and MTC N1 within 19 and 31 years, respectively[18]. Prophylactic thyroidectomy is recommended before the age of 5 years. However, clinicians must carefully weigh the risk of surgical complications in children, increased recurrence rates during lymph node dissection, and the probability of cure[19,20]. Monitoring calcitonin level is another crucial evaluation standard. A French study of 170 young patients aged < 21 years confirmed the major role of calcitonin testing in prophylactic thyroidectomies, indicating that all preoperative patients with calcitonin levels < 30 pg/mL, regardless of whether their MTC was classified as extremely high-, high-, or medium-risk, were cured after thyroidectomy[21].

Raue and Frank-Raue[22] suggested a three-point management strategy for patients with MEN2: (1) Confirm the pathogenic RET gene mutation type; (2) classify MTC risk groups; and (3) determine preoperative calcitonin levels to ensure that asymptomatic carriers undergo timely MTC removal. Both high- and moderate-risk groups could determine the timing of surgery based on calcitonin level[21-24]. Once the calcitonin levels surpass the upper limit of normal level, surgery can be performed. This approach may postpone thyroidectomy until the patient reaches full growth, thereby reducing surgical complications, such as permanent hypoparathyroidism and recurrent laryngeal nerve injury, and preventing overtreatment.

In the family with MEN2A discussed in this study, three members harbored a heterozygous mutation of nucleotide c.T1901A, which caused the 634^th amino acid of the encoded protein to mutate from cysteine to tyrosine. Among the mutations in codon 634, the C634Y mutation is uncommon and may present a more indolent clinical course. In this family with the high-risk C634Y mutation, proband IIa first presented with pheochromocytoma. Given the patient’s age of 30 years, the atypical presentation of calcitonin levels, and color Doppler ultrasound findings, a thyroidectomy was performed. Postoperative pathological examination confirmed the presence of MTC without lymph node metastasis. A 5-year follow-up revealed normal calcitonin levels and thyroid color Doppler ultrasound findings, with no signs of recurrence. Regular follow-ups with abdominal CT and MN levels were also normal, with no pheochromocytoma or pheochromocytic tissue, suggesting a benign pheochromocytoma. The proband's father, who had a history of hypertension and did not participate in regular health examinations, was found to have an RET gene C634Y mutation through genetic testing. This finding led to surgical intervention for the pheochromocytoma and MTC, both of which were pathologically confirmed. However, owing to the advanced age at which testing was conducted, the MTC had already metastasized to the lymph nodes, necessitating stringent monitoring of calcitonin levels to prevent recurrence. The gene mutation carrier IIIa harbors a high-risk mutation. According to the guidelines, total thyroidectomy can be performed before the age of 5 years; however, given the child's growth and developmental needs, along with relatively higher surgical risks, and in accordance with the family's wishes, we opted to closely monitor calcitonin level and thyroid color Doppler ultrasound. After 5 years of follow-up, an increase in calcitonin level was detected when the child turned 9 years old, necessitating a prophylactic thyroidectomy. Subsequent pathological examination confirmed the presence of MTC.

The thyroid conditions of the three aforementioned patients were managed in accordance with the American Thyroid Association guidelines, considering the genotype–phenotype relationship of MEN2A, which effectively guided clinical diagnosis and treatment. At the time of diagnosis of the disease in the proband, she was diagnosed with bilateral pheochromocytomas, whereas her father had a unilateral pheochromocytoma. These findings align with previous reports on MEN2A pheochromocytomas, which can be either unilateral or bilateral, with rare malignancies. None of the three patients exhibited signs of hyperparathyroidism, thereby necessitating long-term monitoring of blood calcium and PTH levels and parathyroid color Doppler ultrasonography.

In this report, we highlight that gene detection in three generations of a family can be used for early screening of related diseases, especially for the diagnosis and treatment of early medullary thyroid cancer. However, owing to the limited number of patients, there are certain limitations, and it will be more meaningful to screen the genes and related diseases in Ia parents and siblings.

In summary, RET proto-oncogene mutations play crucial roles in determining the clinical phenotype and prognosis of patients with MEN2A. In a clinical setting, advancements in genetic research on MEN2A can be leveraged for familial management; assess the invasive risk of MTC based on RET gene mutation types, age, and calcitonin levels; and decide the timing of surgery. This study offers considerable guidance regarding the onset, progression, and prognosis of pheochromocytoma and hyperparathyroidism.

We thank the doctors and nurses at the Department of Endocrinology, Guangzhou University of Chinese Medicine, Dongguan TCM Hospital for their help in this study. We express gratitude to our partner, Beijing Hongwei Testing Co., Ltd, for their excellent cooperation and technical support.