Somatic mutations in MEN type 1 tumors, consistent with the Knudson "two-hit" hypothesis

MEN type 1 is an autosomal dominant disorder characterized by the combined occurrence of tumors of the parathyroids, anterior pituitary, and pancreatic islet cells. The MEN1 gene, which is located on chromosome 11q13, consists of 10 exons and encodes a 610-amino acid protein named MENIN. The observation of LOH involving 11q13 in MEN type 1 tumors and the inactivating germline mutations found in patients suggest that the MEN1 gene acts as a tumor suppressor, in keeping with the "two-hit" model of hereditary cancer. The second hit in MEN type 1 tumors typically involves large chromosomal deletions that include 11q13. However, this only represents one mechanism by which the second hit may occur, and the other mechanisms, such as intragenic deletions or point mutations that inactivate the gene, have not been reported in MEN type 1 tumors. We have therefore undertaken studies to search for such mutations in six MEN type 1 tumors (four parathyroid tumors, one insulinoma, and one lipoma) that did not have LOH at 11q13 as assessed using the flanking markers D11S480, D11S1883 and PYGM centromerically and D11S449 and D11S913 telomerically. This revealed four somatic mutations, which consisted of two missense mutations and two frameshift mutations in two parathyroid tumors, one insulinoma, and one lipoma. Thus, our results, which represent the first small intragenic somatic mutations reported in MEN type 1 tumors, provide further evidence that the role of the MEN1 gene is consistent with that of a tumor suppressor gene, as postulated by Knudson's "two-hit" hypothesis.     

Two novel mutations in the MEN1 gene in subjects with multiple endocrine neoplasia-1

Multiple endocrine neoplasia type 1 (MEN1) is characterized by parathyroid, enteropancreatic endocrine and pituitary adenomas as well as germline mutation of the MEN1 gene. We describe 2 families with MEN1 with novel mutations in the MEN1 gene. One family was of Turkish origin, and the index patient had primary hyperparathyroidism (PHPT) plus a prolactinoma; three relatives had PHPT only. The index patient in the second family was a 46-yr-old woman of Chinese origin living in Taiwan. This patient presented with a complaint of epigastric pain and watery diarrhea over the past 3 months, and had undergone subtotal parathyroidectomy and enucleation of pancreatic islet cell tumor about 10 yr before. There was also a prolactinoma. Sequence analysis of the MEN1 gene from leukocyte genomic DNA revealed heterozygous mutations in both probands. The Turkish patient and her affected relatives all had a heterozygous A to G transition at codon 557 (AAG-->GAG) of exon 10 of MEN1 that results in a replacement of lysine by glutamic acid. The Chinese index patient and one of her siblings had a heterozygous mutation at codon 418 of exon 9 (GAC-->TAT) that results in a substitution of aspartic acid by tyrosine. In conclusion, we have identified 2 novel missense mutations in the MEN1 gene.     

No evidence of germline mutation or somatic deletion of the MEN1 gene in a case of familial multiple endocrine neoplasia type 1 (MEN1)

The MEN1 gene has recently been cloned as the gene responsible for multiple endocrine neoplasia type 1 (MEN1) and its germline mutations have been identified in a number of familial MEN1 patients. However, mutation-negative cases have also been reported in some MEN1 families. We report here a Japanese MEN1 family, including a proband with no evidence of MEN1 gene mutation. The proband (51 y.o., female) had three major MEN1 lesions, including primary hyperparathyroidism (HP), prolactinoma, and pancreatic tumor. Her father and brother had HP, and her daughter had both HP and prolactinoma. When we analyzed the proband for a germline mutation of the MEN1 gene, the direct sequencing analysis showed no mutation in the coding region, on the promoter, 5' and 3' untranslated regions of the MEN1 gene. We next examined the loss of heterozygosity (LOH) in the proband's parathyroid tumors using two benign polymorphisms (C2249G in intron 1 and 2248del3 in exon 10) in the MEN1 gene to detect LOH. LOH was not found in any of the four separate regions of the tumor tissues.     

Germline MEN1 mutations in sixteen Japanese families with multiple endocrine neoplasia type 1 (MEN1)

OBJECTIVE: Multiple endocrine neoplasia type 1 (MEN1) is a syndrome of endocrine tumors involving the parathyroids, anterior pituitary and enteropancreatic neuroendocrine tissues, and is inherited in an autosomal dominant manner. Recently, the gene responsible for this syndrome, MEN1, was positionally cloned in 11q13. We aimed to assess the significance of MEN1 gene diagnostics in families with MEN1. DESIGN: Sixteen probands of familial MEN1 and their 40 family members were subjected to the study. METHODS: Full-length sequencing of the open reading frame and exon-intron boundaries in the MEN1 gene was performed with probands of familial MEN1. Family members were examined for the identified mutation in the proband. RESULTS: We identified heterozygous germline mutations of the MEN1 gene in all of 16 Japanese MEN1 families examined, achieving the highest detectability of MEN1 mutations in familial MEN1 among studies that examined more than 10 families. Eleven kinds of the identified MEN1 germline mutations were novel. More than half were nonsense or frameshift mutations resulting in a premature stop codon (9/15; 60%), and no mutation hot spots or no apparent genotype-phenotype relationships were observed, in support of the results of other studies. We identified 40 mutant MEN1 gene carriers and 16 non-carriers in the course of the present study in those families. CONCLUSIONS: Analysis of the germline mutations in the MEN1 gene, providing significantly useful clinical information to probands and family members of MEN1, should be considered as a standard procedure and categorized as belonging to Group 1 cancer predisposition testing by the American Society of Clinical Oncology.     

Frequent occurrence of an intron 4 mutation in multiple endocrine neoplasia type 1

MEN1 is an autosomal dominant disorder characterized by parathyroid, pituitary, and pancreatic tumors. The MEN1 gene is located on chromosome 11q13 and encodes a 610-amino acid protein. MEN1 mutations are of diverse types and are scattered throughout the coding region, such that almost every MEN1 family will have its individual mutation. To further characterize such mutations we ascertained 34 unrelated MEN1 probands and undertook DNA sequence analysis. This identified 17 different mutations in 24 probands (2 nonsense, 2 missense, 2 in-frame deletions, 5 frameshift deletions, 1 frameshift deletional-insertion, 3 frameshift insertions, 1 donor splice site mutation, and a g-->a transition that resulted in a novel acceptor splice site in intron 4). The intron 4 mutation was found in 7 unrelated families, and the tumors in these families varied considerably, indicating a lack of genotype-phenotype correlation. However, this intron 4 mutation is the most frequently occurring germline MEN1 mutation ( approximately 10% of all mutations), and together with 5 others at codons 83-84, 118-119, 209-211, 418, and 516, accounts for 36.6% of all mutations, a finding that indicates an approach for identifying the widely diverse MEN1 mutations.     

A novel germline mutation of multiple endocrine neoplasia type 1 (MEN1) gene in a Japanese MEN1 patient and her daughter.

Familial multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant inherited disorder characterized by tumors of the parathyroid, anterior pituitary and gastro-entero-pancreatic endocrine tissues. The MEN1 gene has recently been cloned and its germline mutations have been considered to play an important role in the tumorigenesis of MEN1. We analyzed a Japanese MEN1 patient and her daughter for germline mutations of the MEN1 gene. The proband (60 y.o.) had primary hyperparathyroidism (PHP) and gastrinoma, and her daughter (30 y.o.) had prolactinoma. Clinical examinations revealed no evidence of PHP in the daughter. We identified a novel heterozygous germline mutation (712 A del) at codon 201 in exon 3 of the MEN1 gene in the proband. Restriction digestion analysis revealed the same mutation pattern in her daughter. These findings suggest that this family has familial MEN1 including a rare case of MEN1 with a single lesion of the pituitary. Genetic examinations are useful as diagnostic tools for any rare or variant case of familial MEN1.     

RET proto-oncogene mutations are restricted to codons 634 and 918 in mainland Chinese families with MEN2A and MEN2B

OBJECTIVE: Multiple endocrine neoplasia type 2 is caused by autosomal dominant gain-of-function mutations in the RET proto-oncogene, which includes multiple endocrine neoplasia type 2A (MEN2A), type 2B (MEN 2B), and familial medullary thyroid carcinoma (FMTC). In this paper we present the phenotype-genotype correlation of 20 unrelated Chinese families with 15 cases of MEN2A and five cases of MEN2B. DESIGN: Cross-sectional study. PATIENTS: A total of 147 members from the 20 families were included. Among them, 119 family members were from MEN2A pedigrees (including 15 MEN2A probands) and 28 members from MEN2B pedigrees (including five MEN2B probands). MEASUREMENTS: Genomic DNA was isolated from peripheral blood leucocytes and was amplified using polymerase chain reaction (PCR). DNA analysis for RET mutations in exons 8, 10, 11, 13, 14, 15 and 16 was performed with specific primers. RESULTS: Thirty-seven MEN2A and five MEN2B patients were identified as having RET mutations. The incidence of medullary thyroid carcinoma (MTC), pheochromocytoma (PCC) and hyperparathyroidism (HPT) in the 37 MEN2A patients was 91.9, 56.8 and 10.8%, respectively; the onset of MTC in MEN2A patients was earlier than that of PCC and HPT. Five germline mutations, all located at codon 634 of exon11 in the RET proto-oncogene, were detected in all of the 37 MEN2A patients. The highest frequency of the five germline mutations was C634Y (46.7%), followed by C634R (26.7%), C634W (13.3%), C634F (6.7%) and C634S (6.7%). No statistical significance was found between the incidence of PCC and different genotypes of codon 634 in MEN2A patients, whereas the incidence of HPT was closely associated with C634R and C634Y. The gene mutation (M918T) at exon16 of the RET proto-oncogene was present in five MEN2B probands. CONCLUSIONS: RET proto-oncogene mutations were restricted to codon 634 and 918 in Chinese families with MEN2A and MEN2B. In general the genetic characteristics of these patients with MEN2A and MEN2B reflect the general pattern around the world and it remains to be determined with larger studies in China whether Chinese patients have a different genetic pattern of mutations.     

Novel mutations in the MEN1 gene in subjects with multiple endocrine neoplasia-1

OBJECTIVE: To identify MEN1 gene mutations and characterize clinical manifestations in Chinese kindred with multiple endocrine neoplasia type 1 (MEN1) in Taiwan. PATIENTS AND METHODS: Eight unrelated subjects (one male and seven females, age range 26-70 years) with clinical manifestations of MEN1 were analysed. In addition, 45 relatives that included 10 affected (three males and seven females, age range 32-53 years) and 35 unaffected (17 males and 18 females, age range 15-80 years) subjects were evaluated. Genomic DNA extraction, polymerase chain reaction (PCR) and DNA sequence analysis were performed according to standard procedures. RESULTS: We identified heterozygous MEN1 gene mutations in all eight probands and 10 affected subjects as well as in 13 clinically asymptomatic relatives. Novel mutations included a missense mutation in a heterozygous mutation in exon 9 (GAC --> CAC) resulting in a substitution of aspartic acid by histidine at codon 418 (family 1); a nonsense mutation at codon 556 of exon 10 (GAG --> TAG) resulting in a stop codon and termination (family 2); a missense mutation in exon 2 (GGG --> GAG) causing the substitution of glycine by glutamic acid at codon 110 (family 3); and a deletion/insertion mutation in nucleotide 1200 of exon 8 resulting in frameshift and early termination (family 4). Affected subjects in families 5-7 shared the same C insertion at nucleotide 1650 of exon 10, similar to that previously described as a hotspot for mutation, and proband 8 had a previously described mutation in intron 4 of the MEN1 gene (IVS4-9 G --> A). We also found that 18 (58%) of our 31 MEN1 mutant carriers had clinical symptoms, whereas four (13%) had biochemical abnormalities without clinical symptoms, and nine (29%) were unaffected both clinically and biochemically. CONCLUSIONS: We have identified four novel mutations in the MEN1 gene in patients with MEN1 in Taiwan.     

Germline mutation of the multiple endocrine neoplasia type 1 (MEN1) gene in a family with primary hyperparathyroidism.

Familial primary hyperparathyroidism (FHP) is a rare hereditary disorder characterized by isolated parathyroid tumors without any other lesions related to multiple endocrine neoplasia (MEN). Primary hyperparathyroidism is usually expressed at an early age and is highly penetrated in MEN type 1 (MEN1), suggesting that some FHP may be a variant type or early stage of MEN1. The MEN1 gene has recently been cloned and its germline mutations have been considered to play an important role in the tumorigenesis of MEN1. We studied a Japanese family with primary hyperparathyroidism which included 4 patients. To investigate the possible relationship between primary hyperparathyroidism in this family and the MEN1 gene, we analyzed a proband for a germline mutation of the MEN1 gene in this study. We identified a novel heterozygous mutation (1350del3) at codon 414 in exon 9. Restriction digestion analysis revealed the same mutation pattern in his brother with hyperparathyroidism. These findings suggest that our patients may belong to a variant type of MEN1.     

Multiple endocrine neoplasia type 1 (MEN1) germline mutations in familial isolated primary hyperparathyroidism

BACKGROUND: Familial isolated hyperparathyroidism (FIHP) is an autosomal dominant disorder characterized by uniglandular or multiglandular parathyroid tumours that occur in the absence of other endocrine tumours. The disorder may represent either an early stage of multiple endocrine neoplasia type 1 (MEN1), or an allelic variant of MEN1, or a distinct entity involving another locus. We have explored these possibilities in seven families in whom primary hyperparathyroidism occurred as the sole endocrinopathy. METHODS: Seven FIHP families were ascertained and venous blood samples obtained from 35 members (17 affected and 18 unaffected) for DNA sequence analysis of the MEN1 gene. The mean (+/- SD) follow-up period in the 17 affected members was 15.06 (+/- 8.83) years. RESULTS: Four heterozygous germline mutations of the MEN1 gene were identified. These consisted of two 4-bp intragenic deletions that would result in prematurely truncated proteins, and two missense (Asp153Val and Ala411Pro) mutations. Furthermore, analysis of parathyroid tumour DNA from one individual revealed a loss of the wild-type allele and retention of the mutant allele, consistent with Knudson's 'two-hit' model of hereditary cancer and a tumour suppressor role for MEN1 in FIHP. CONCLUSIONS: Our results provide further support for FIHP being a distinct allelic variant of MEN1, and an analysis of the 16 mutations reported to date indicate that FIHP is associated with a higher frequency of missense MEN1 mutations.     

Ret proto-oncogene mutations in apparently sporadic Turkish medullary thyroid carcinoma patients: Turkmen study

OBJECTIVE: Medullary thyroid carcinoma (MTC) frequently occurs in a sporadic form, but a substantial number of cases are hereditary and appear as part of the multiple endocrine neoplasia type 2 (MEN2) syndromes. Germline mutations in ret proto-oncogene have been shown to be the underlying cause of MEN2 syndromes. DESIGN: We carried out a multi-center study that aimed to perform mutational analysis of so called sporadic MTC patients. METHODS: Fifty-six MTC patients verified by histopathologic examination were subjected to genetic analysis. Exon 10, 11, 13, 14, 15 and 16 of the ret gene were analyzed by DNA sequencing and restriction enzyme digestion method. RESULTS: Among 56 apparently sporadic MTC patients, we identified 6 (10.7%) ret germline mutation carriers. Three individuals carried mutations at codon 634 in exon 11, one at codon 618 in exon 10, and two at codon 804 in exon 14. Identification of the predisposition gene mutation has allowed DNA-based strategy for direct mutation detection in patients with apparently sporadic MTCs. A substantial number of patients with apparently sporadic MTC carried germline mutations and 50% of their first degree relatives are expected to have or to develop MTC and/or other endocrine tumors. CONCLUSIONS: These results indicate the importance of careful genetic surveillance of any patient with apparently sporadic MTCs.     

RET proto-oncogene mutations are restricted to codon 634 and 618 in Korean families with multiple endocrine neoplasia 2A.

Identification of the germline mutation in the RET proto-oncogene is important for the diagnosis of hereditary medullary thyroid carcinoma (MTC). Hereditary forms account for approximately 25%-30% of all cases of MTC. The objective of this study was to evaluate the prevalence of the RET mutation and the genotype-phenotype relation in Korean patients with MTC. Genomic DNAs were obtained from 33 patients with MTC (M:F = 10:23, 39.8 +/- 12.0 years) who underwent total thyroidectomy between 1997 and 2003 at the Samsung Medical Center. Exons 10, 11, 13, 14, 15 and 16 of the RET proto-oncogene were amplified with specific primers using polymerase chain reaction (PCR). Sequence analysis was performed on the polymerase chain reaction (PCR) product using an automatic sequence analyzer. Nine of the 33 patients (M:F = 3:6, 33.3 +/- 10.0 years) were identified as having RET mutations. Six patients had multiple endocrine neoplasia (MEN) 2A and one had familial medullary thyroid carcinoma (FMTC). The remaining two patients were thought to have sporadic MTC. Five of the patients with MEN 2A had RET mutations in codon 634 of exon 11 (3 patients, C634Y; 2 patients, C634R) and the other patient with MEN 2A had a RET mutation in codon 618 of exon 10 (C618R). The patient with FMTC had a mutation in codon 634 (C634W). The two patients with sporadic MTC had RET mutations in codon 634 (1 patient, C634Y; 1 patient, C634S). We were not able to identify any genotype-phenotype relations because of the limited number of patients. Twenty-seven percent (9/33) of the patients with MTC in this study had RET mutations. Taking other studies into account, 77% (10/13) of Korean families with MEN 2A, including 7 other families in three reports from Korea, had RET mutations in codon 634 (5 families, C634Y; 4 families, C634R; 1 family, C634W), and 23% (3/13) had RET mutations in codon 618 (2 families, C618R; 1 family, C618S). RET proto-oncogene mutations were restricted to codon 634 and 618 in Korean families with MEN 2A.     

Genetic analyses in patients with familial isolated hyperparathyroidism and hyperparathyroidism-jaw tumour syndrome

BACKGROUND: A subset of familial isolated primary hyperparathyroidism (FIHP) is a variant of hyperparathyroidism-jaw tumour syndrome (HPT-JT). AIM/PATIENTS AND METHODS: We investigated the involvement of the HRPT2, MEN1 and CASR genes in 11 provisional FIHP families and two HPT-JT families. RESULTS: Germline mutations of HRPT2 were found in two of the 11 FIHP families and one of the two HPT-JT families. One FIHP family with parathyroid carcinoma and atypical adenomas and another FIHP family with cystic parathyroid adenoma had novel frameshift mutations of 518-521del and 62-66del, respectively. In a patient with HPT-JT, a de novo germline mutation of 39delC was detected. Novel somatic HRPT2 mutations of 70-73del and 95-102del were found in two of five parathyroid tumours in a family with a 518-521del mutation. Biallelic inactivation of HRPT2 by a combination of germline and somatic mutation was confirmed in the parathyroid tumours. The finding that two families diagnosed with FIHP carried HRPT2 mutations suggests that they have occult HPT-JT. In the remaining 10 families, one family had a missense MEN1 mutation. No mutations of CASR were detected. CONCLUSION: Our results confirm the need to test for HRPT2 in FIHP families, especially those with parathyroid carcinomas, atypical adenomas or adenomas with cystic change.     

Coexistence of multiple endocrine neoplasia type 1 and type 2 in a large Italian family

To describe the coexistence of mutations of both the multiple endocrine neoplasia type 1 (MEN1) and type 2 (MEN2) genes in a large Italian family and evaluate if it could be associated with more aggressive clinical manifestations of the two syndromes. Blood samples were obtained for genetic and biochemical analyses. The RET gene exons (8, 10, 11, 13, 14, 15, 16, 18) and the MEN1 coding regions, including the exon-intron boundaries, were amplified by PCR and directly sequenced. We identified two germline mutations in the proband: the first one, K666M, located at the exon 11 of RET proto-oncogene and the second one, IVS4+1G>T, located in the MEN1 gene. The functional characterization of IVS4+1G>T variation, located in the splicing donor site of exon 4 of MEN1 gene, caused the in-frame junction of exon 3 to exon 5, thus obtaining a shorter protein. The same proband's germline mutations were found in 16 relatives out of 21 screened subjects: 8 carried IVS4+1G>T, 4 RET K666M, and 4 both the mutations. This is the second report in literature of coexistence in the same family of germline mutations of both RET proto-oncogene and MEN1 gene. The simultaneous presence of the two mutations was not apparently associated with more aggressive diseases, since at last follow-up all patients appeared to be disease-free or well compensated by medical therapy; finally, no one exhibited metastatic diseases.     

Frequency of somatic MEN1 gene mutations in monoclonal parathyroid tumours of patients with primary hyperparathyroidism

OBJECTIVES: Investigation of small numbers of parathyroid tumours by X-chromosome inactivation analysis suggests that the majority of them are monoclonal lesions most likely caused by a somatic mutation. Somatic mutations in the MEN1 gene located on chromosome 11q13 have recently been identified in 12-17% of solitary parathyroid tumours in patients with sporadic primary hyperparathyroidism, and they may be the precipitating genetic defect leading to monoclonal cell proliferation in these tumours. DESIGN: To determine the prevalence of MEN1 gene mutations in monoclonal parathyroid neoplasias we investigated 33 parathyroid tumours of patients with primary hyperparathyroidism for clonality and mutations in the MEN1 gene. METHODS: X-chromosome inactivation analysis was used to assess the clonal status of the tumours, direct sequencing of the complete coding region was applied to identify mutations in the MEN1 gene. RESULTS: Twenty-eight female patients (26 patients with solitary adenoma, 2 patients with hyperplasia) were informative for the polymorphism of the androgen receptor on the X-chromosome and could be tested for inactivation pattern. Nineteen of twenty-six (73%) solitary adenomas were monoclonal. Somatic mutations in the MEN1 gene were identified in nine cases. Six of them were found in the relatively large second exon of the MEN1 gene (A49D, 193del36, 402delC, 482del22, 547delT, W126X). One was found in exon 5 (904del9), one in exon 7 (Y327X) and one in exon 9 (R415X). Of the monoclonal tumours, 5 out of 19 (26%) harboured a somatic MEN1 gene mutation. CONCLUSIONS: In summary, 73% of the solitary parathyroid adenomas were monoclonal. In 26% of the monoclonal tumours a somatic MEN1 gene mutation has been identified. However, for 74% of monoclonal tumours of the parathyroids the underlying genetic defects are still not known.     

Novel somatic MEN1 gene alterations in sporadic primary hyperparathyroidism and correlation with clinical characteristics

Primary hyperparathyroidism (pHPT) is a common endocrine disease that in more than 95% of cases is sporadic and only in some cases is caused by inherited disorders, isolated or as part of multiple endocrine neoplasia (MEN1 and 2). Somatic mutations of MEN1 gene have also been described in sporadic parathyroid tumors. In our study, we examined the presence of alterations in MEN1 gene in a series of 39 patients who had undergone surgery for sporadic pHPT (35 with parathyroid adenoma or hyperplasia, 4 with a carcinoma). A genotype-phenotype correlation was also analysed. After DNA extraction from paraffin-embedded tissues, we amplified by PCR and sequenced the exons 2-10 of the MEN1 gene. Somatic MEN1 mutations were detected in 6 of the 35 patients with a benign parathyroid lesion examined (17.1%), whereas no alterations were found in the carcinomas. Four novel MEN1 gene mutations were identified as follows: one frameshift mutation (222insT, exon 2), one frameshift deletion (912delTA, exon 5), one in-frame deletion (835del18, exon 4) and one missense mutation (P291A, exon 6). In addition, one missense mutation (L89R, exon 2) and one nonsense mutation (Q536X, exon 10) were previously reported. Moreover, two polymorphisms were also found: one allele carried a R171Q polymorphism (1/39 tumors), while a D418D polymorphism (GAC/GAT) was found in 15 and 8 tumors in hetero (CT) and homozygosity (TT), respectively. In no case (mutations and/or polymorphisms) did we find a genotype-phenotype correlation. In conclusion, our data demonstrate the presence of somatic alterations of the MEN1 tumor suppressor gene in about one fifth of benign sporadic parathyroid tumors. The absence of a genotype-phenotype correlation, however, suggests the involvement of other genetic/epigenetic factors for the full expression of the disease.     

Two novel germline mutations of MLH1 and investigation of their pathobiology in hereditary non-polyposis colorectal cancer families in China

AIM： To detect germline mutations of MLH1, and investigate microsatellite instability and expression of MLH1 in tumor tissues of hereditary non-polyposis colorectal cancer （HNPCC） with two novel germline mutations, and further investigate the pathobiology of the two novel mutations of MLH1. METHODS： RNA was extracted from the peripheral blood of 12 patients from 12 different families that fulfilled the Amsterdam 11 Criteria for HNPCC. Germline mutations of MLH1 were determined by RT-PCR, followed by cDNA sequencing analysis. PCR-GeneScan analysis was used to investigate microsatellite instability with a panel of five microsatellite markers （BAT26, BAT25, D5S346, D2S123 and mfd15）, along with immunohistochemical staining to detect the expression of MLH1 protein in two patients＇ tumor tissues with novel mutations. RESULTS： Three germline mutations were found in four patients, one of the mutations has previously been reported, but the other two, CGC→TGC at codon 217 of exon 8 and CCG→CTG at codon 581 of exon 16, have not been reported. The two patients＇ tumor tissues with novel mutations had high-frequency microsatellite instability that showed more than two unstable loci, and both tumors lost their MLH1 protein expression. CONCLUSION： The two novel germline mutations of MLH1 in HNPCC families i.e. CGC→TGC at codon 217 of exon 8 and CCG→CTG at codon 581 of exon 16, are very likely to have pathological significance.