In this study, we found a proband with typical tumor symptoms of MEN1, including a pancreatic tumor, parathyroid tumor, adrenal tumor, and suspicious gastrinoma, as well as pituitary changes. Subsequently, the proband tested the gene of MEN1 by WES, and found that there's a new gene mutation in exon2 of MEN1, which could lead to these clinical symptoms. Due to the heritability of MEN1, the proband's family members tested the MEN1 by Sanger sequence. Subsequently, we found that this Chinese family carry on MEN1 and found a new germline mutation of NM_130802 [c.201delC (p.Ala68Profs*51) on Chr11:64577381 on assembly GRCh37].
Because of the results of gene test, we recommended the proband’s family members be hospitalized for screening disease related to MEN1. Only the proband’s sister (51-year-old) accepted our recommendation for hospitalization. After several examination the same as proband, we found the proband’s sister with typical tumor symptoms of MEN1 as well, including a pancreatic tumor and a parathyroid tumor. The proband and her sister's typically clinical symptoms indicated that the MEN1 gene mutation in this Chinese family. However, due to some force majeure factor, the niece of the proband (III-1) rejected the recommendation of being hospitalized for screening the disease related to MEN1. In addition, any clinical symptoms related to MEN1 hadn't appeared. It may be because the MEN1-related tumor is not serious or her age wasn't too old enough. Therefore, we recommended her to get hospitalized for screening the disease related to MEN1 as soon as possible when she have space time.
As we all know, the MEN1 gene plays a role as a growth suppressor in MEN1 tumorigenesis. In the germline, an inactivated mutation in the MEN1 gene on chromosome 11 causes MEN1 syndrome. About 90% of MEN1 cases are usually inherited from affected parents; the other 10% of cases are due to a de novo mutation (9). The loss of heterozygotes at the MENIN site on chromosome 11q13 showed biallelic inactivation of MEN1 (14). Knudson’s two-hit model of MEN1 gene tumorigenesis (2, 3, 15) is supported by the harmful germline mutations observed in the MEN1 kindreds and the loss of wild-type alleles observed in the tumors of MEN1 patients in a MEN1 family. Since the cloning of the MEN1 gene in 1997, more than 1,000 families have been reported as MEN1 (16). Marini et al. reported an analysis of MEN1 mutations in 410 patients’ germlines. It was found that there were 99 different mutations, of which 41 were frameshift, 26 missense, 13 nonsense, 11 splice site mutations, 4 in-frame small deletions, and 4 large intragenic deletions across one exon (17). In 2008, Lemos and Thakker conducted a comprehensive analysis of 1336 MEN1 mutations that had been reported in the first decade after the identification of the MEN1 gene (16). Paola Concolino et al. reported 208 new germline variants of MEN1 from 2007–2015 (18). No other similar papers were available in the literature apart from these MEN1 genetic mutation-related data. We found the MEN1 genetic mutation c.201delC (p.Ala68Profs*51) to be a new germline mutation site in exon 2 that had not yet been reported.
Interestingly, the very rare situation in this family is that the proband has the genetic mutation in exon 2, with the intron 1 changed meantime. By coincidence, the primer region that we designed for WES was consistent with the changed intron 1 region (MEN1-Exon2-1F, 2F), which led to a homozygous mutation of MEN1 in the genetic detection results, that could not be explained by Mendelian law of inheritance.
In the MEN1 gene, the most mutated exons are 2, 9, and 10. In particular, in exons 2 and 10, the most common type of mutation is a frameshift (18). Most of the frameshift and nonsense mutations cause protein truncation, resulting in the loss of functional domains, including NLSs located at the C-terminal segment. In the past few years, six new intron variants have been found in MEN1 patients. One of the intron variants (IVS3 + 18C > T) relates to a c.1546-1547insC mutation in a Chinese MEN1 family, which was reported by Zha et al. (19). Zhiwei Ning et al. (13) found a germline mutation of a heterozygous G to A variation at the nucleotide position-1 of intron 5 (c.825-1G > A or IVS5-1G > A) in a MEN1 family. In this study, because of the change in intron 1, homozygous mutations were found twice by WES. Therefore, we have reason to believe that intron 1 was also mutated. However, the new intron nucleotide mutation could be a polymorphism, and since introns have limited meaning in the structure of translation products, the mutations in the intron were not detected.
Gross deletions, usually detected by the MLPA technique (20–23), are the rarest kind of MEN1 mutation. The complete MEN1 gene deletion has been considered by different authors (20, 24, 25). The first (exons 1–3) (22, 23), central (exons 5–6) (21), and final (exons 8–10) regions of the gene (26) have been described by other gross deletions. Beijers et al. (12) were the first to report on a family with combined germline and somatic mosaicism for MEN1. They used MLPA to analyze the father and found both germline and somatic mosaicism of MEN1. Hence, it is necessary to use MLPA in MEN1 families who are difficult to diagnose. In this study, the MLPA results confirm that there were no significant gross deletions in the MEN1 gene in this family.