CHK2 1100delC,IVS2 + 1G>A and I157T mutations are not present in hepatocellular cancer cases from a Turkish population

Aim

The cell cycle checkpoint kinase 2 (CHK2) protein participates in the DNA damage response in many cell types. Germline mutations in CHK2 (1100delC, IVS2 + 1G>A and I157T) have been associated with a range of cancer types. This study aimed to investigate whether CHK2 1100delC, IVS2 + 1G>A and I157T mutations play an important role in the development of hepatocellular carcinoma (HCC) in a Turkish population.

Methods

A total of 165 hepatocellular cancer cases and 446 cancer-free controls were genotyped for CHK2 mutations by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and allele specific-polymerase chain reaction (AS-PCR) methods.

Results

We did not find CHK2 1100delC, IVS2 + 1G>A and I157T mutations in any of 611 Turkish subjects.

Conclusion

Our results demonstrate for the first time that CHK2 1100delC, IVS2 + 1G>A and I157T mutations have not been a genetic susceptibility factor for HCC in the Turkish population. Overall, our data suggests that genotyping of CHK2 mutations in clinical settings in the Turkish population should not be recommended. Independent studies are needed to validate our findings in a larger series, as well as in patients of different ethnic origins.     

Frequency of CHEK2 gene mutations in breast cancer patients from Republic of Bashkortostan

A number of studies demonstrated that mutations in the CHEK2 gene can increase the risk of oncologic diseases, including breast cancer and that the mutational distribution s depends on the genetic structure of populations. In our study we compared the prevalence of c.1100delC, c.444+1G>A, del5395, p.I157T, and p.R145W CHEK2 mutations in 977 breast cancer patients (Russians, Tatars, Bashkirs, Ukrainians, and individual representatives of other ethnic groups) and in women without any oncologic pathology (n = 1069) from the Republic of Bashkortostan. We found CHEK2 del5395 mutation with a frequency of 1.23% (12/977) in breast-cancer patients, whereas in the control group it frequency was 0.09% (1/1069) (OR: 13.28, CI 95%: 1.72–102.33, p = 0.003). Frequencies of c.1100delC and c.444+1G>A mutations in patients and controls were 0.4%, 0.4% (4/977) and 0.09% (1/1069), 0.2% (2/1069), respectively. The p.I157T substitution in CHEK2 gene was the most widespread variant in two studied cohorts (approximately 5%); however, differences in the frequencies between cases and controls did not reach statistical significance. Truncating mutations were mainly found in women of Slavic origin. All three mutations were found in Russians and Ukrainians. CHEK2 mutations c.1100delC and c.444+1G>A were not found in Bashkirs and Tatars; however, the CHEK2 del5395 deletion was present in Tatars.     

CHEK2 gene alterations in the forkhead-associated domain, 1100delC and del5395 do not modify the risk of sporadic pancreatic cancer

Checkpoint kinase 2 gene (CHEK2) alterations increase risk of several cancer types. We analyzed selected CHEK2 alterations in 270 Czech pancreatic cancer patients and in 683 healthy controls. The pancreatic cancer risk was higher in individuals who inherited rare alterations in CHEK2 region involving forkhead-associated domain other than I157T (OR = 5.14; 95% CI = 0.94–28.23) but the observed association was non-significant (p = 0.057). The most frequent I157T mutation did not alter the pancreatic cancer risk and neither the followed deletion of 5395 bp nor c.1100delC were found in any of pancreatic cases. We conclude that the I157T, other alterations in its proximity, del5395 and c.1100delC in CHEK2 do not predispose to pancreatic cancer risk in the Czech population.     

Variants in CHEK2 other than 1100delC do not make a major contribution to breast cancer susceptibility

We recently reported that a sequence variant in the cell-cycle-checkpoint kinase CHEK2 (CHEK2 1100delC) is a low-penetrance breast cancer-susceptibility allele in noncarriers of BRCA1 or BRCA2 mutations. To investigate whether other CHEK2 variants confer susceptibility to breast cancer, we screened the full CHEK2 coding sequence in BRCA1/2-negative breast cancer cases from 89 pedigrees with three or more cases of breast cancer. We identified one novel germline variant, R117G, in two separate families. To evaluate the possible association of R117G and two germline variants reported elsewhere, R145W and I157T with breast cancer, we screened 737 BRCA1/2-negative familial breast cancer cases from 605 families, 459 BRCA1/2-positive cases from 335 families, and 723 controls from the United Kingdom, the Netherlands, and North America. All three variants were rare in all groups, and none occurred at significantly elevated frequency in familial breast cancer cases compared with controls. These results indicate that 1100delC may be the only CHEK2 allele that makes an appreciable contribution to breast cancer susceptibility.     

Genotyping of BRCA1, BRCA2, and CHEK2 germline mutations in Russian breast cancer patients using diagnostic biochips

The identification of BRCA1/2 and CHEK2 germline mutations is central to the molecular diagnostics of susceptibility to breast or/and ovarian cancer. A microarray-based rapid genotyping technique has been developed for identifying BRCA1 (185delAG, 300T>G, 4153delA, 5382insC, and 4158 A>G, 5382insC), BRCA2 (695insT and 6174delT), and CHEK2 (1100delC) mutations. It was applied for 412 randomly collected breast-cancer specimens from central Russia. In 25 (6.0%) patients, breast cancer was associated with other tumors of, e.g., ovarian, cervical, or colorectal cancer. BRCA1/2 and CHEK2 mutations were detected in 33 breast-cancer patients (8.0%). The most frequent mutations were BRCA1 5382insC, which was found in 16 patients (3.9%), and CHEK2 1100delC, which was detected in seven patients (1.7%). The suggested diagnostic microarray proved to be an efficient means of identifying BRCA1/2 and CHEK2 founder mutations most frequent in central Russia and can be proposed as a high-throughput diagnostic tool for clinical genetic testing.     

Biochip analysis of BRCA1/2 and CHEK2 common mutations in ovarian cancer and primary multiple tumors involving the ovaries (Russian population)

Ovarian cancer (OC) is among the leading causes of cancer-related mortality in women. A high risk of OC (lifetime estimates ranging 10–60%) is determined by BRCA1/2 mutations. The 1100delC variant of CHEK2 is associated with predisposition to breast cancer (BC) in women. With the known spectrum and frequencies of mutations of these genes, it is possible to identify a risk group in a population. Using biochip technology, the frequencies of eight BRCA1/2 and CHEK2 mutations (185delAG, 300T>G, 4153delA, 4158A>G, and 5382insC of BRCA1; 695insT and 6174delT of BRCA2; and 1100delC of CHEK2) were studied in Russian women with OC, including 68 patients with organ-specific OC and 19 with primary multiple tumors (PMTs) involving the ovaries. Four BRCA1 mutations were observed: 185delAG, 300T>G, 4153delA, and 5382insC. The last one was most common in OC, accounting for 87.5% of all cases with mutant BRCA1, and occurred at a frequency of 50.0% in PMT. BRCA2 and CHEK2 mutations were not found in the two groups.     

A CHEK2 genetic variant contributing to a substantial fraction of familial breast cancer

CHEK2 (previously known as "CHK2") is a cell-cycle-checkpoint kinase that phosphorylates p53 and BRCA1 in response to DNA damage. A protein-truncating mutation, 1100delC in exon 10, which abolishes the kinase function of CHEK2, has been found in families with Li-Fraumeni syndrome (LFS) and in those with a cancer phenotype that is suggestive of LFS, including breast cancer. In the present study, we found that the frequency of 1100delC was 2.0% among an unselected population-based cohort of 1,035 patients with breast cancer. This was slightly, but not significantly (P=.182), higher than the 1.4% frequency found among 1,885 population control subjects. However, a significantly elevated frequency was found among those 358 patients with a positive family history (11/358 [3.1%]; odds ratio [OR] 2.27; 95% confidence interval [CI] 1.11-4.63; P=.021, compared with population controls). Furthermore, patients with bilateral breast cancer were sixfold more likely to be 1100delC carriers than were patients with unilateral cancer (95% CI 1.87-20.32; P=.007). Analysis of the 1100delC variant in an independent set of 507 patients with familial breast cancer with no BRCA1 and BRCA2 mutations confirmed a significantly elevated frequency of 1100delC (28/507 [5.5%]; OR 4.2; 95% CI 2.4-7.2; P=.0002), compared with controls, with a high frequency also seen in patients with only a single affected first-degree relative (18/291 [6.2%]). Finally, tissue microarray analysis indicated that breast tumors from patients with 1100delC mutations show reduced CHEK2 immunostaining. The results suggest that CHEK2 acts as a low-penetrance tumor-suppressor gene in breast cancer and that it makes a significant contribution to familial clustering of breast cancer-including families with only two affected relatives, which are more common than families that include larger numbers of affected women.     

Irrelevance of CHEK2 variants to diagnosis of breast/ovarian cancer predisposition in Polish cohort

CHEK2 gen encodes cell cycle checkpoint kinase 2 that participates in the DNA repair pathway, cell cycle regulation and apoptosis. Mutations in CHEK2 gene may result in kinase inactivation or reduce both catalytic activity and capability of binding other proteins. Some studies indicate that alterations in CHEK2 gene confers increase the risk of breast cancer and some other malignancies, while the results of other studies are inconclusive. Thus the significance of CHEK2 mutations in aetiology of breast cancer is still debatable. The aim of our study was to evaluate the relationship between the breast/ovarian cancer and CHEK2 variants by: i) the analysis of the frequency of selected CHEK2 variants in breast and ovarian cancer patients compared to the controls; ii) evaluation of relationships between the certain CHEK2 variants and clinico-histopathological and pedigree data. The study was performed on 284 breast cancer patients, 113 ovarian cancer patients and 287 healthy women. We revealed the presence of 430T > C, del5395 and IVS2 + 1G > A variants but not 1100delC in individuals from both study and control groups. We did not observe significant differences between cancer patients and controls neither in regard to the frequency nor to the type of CHEK2 variants. We discussed the potential application of CHEK2 variants in the evaluation of breast and ovarian cancer predisposition.     

CHEK2*1100delC and susceptibility to breast cancer: a collaborative analysis involving 10,860 breast cancer cases and 9,065 controls from 10 studies

Previous studies of families with multiple cases of breast cancer have indicated that a frameshift alteration in the CHEK2 gene, 1100delC, is associated with an elevated frequency of breast cancer in such families, but the risk associated with the variant in other situations is uncertain. To evaluate the breast cancer risk associated with this variant, 10,860 breast cancer cases and 9,065 controls from 10 case-control studies in five countries were genotyped. CHEK2*1100delC was found in 201 cases (1.9%) and 64 controls (0.7%) (estimated odds ratio 2.34; 95% CI 1.72–3.20; P=.0000001). There was some evidence of a higher prevalence of CHEK2*1100delC among cases with a first-degree relative affected with breast cancer (odds ratio 1.44; 95% CI 0.93–2.23; P=.10) and of a trend for a higher breast cancer odds ratio at younger ages at diagnosis (P=.002). These results confirm that CHEK2*1100delC confers an increased risk of breast cancer and that this risk is apparent in women unselected for family history. The results are consistent with the hypothesis that CHEK2*1100delC multiplies the risks associated with susceptibility alleles in other genes to increase the risk of breast cancer.     

Ethnic Features of Genetic Susceptibility to Breast Cancer

The results of screening for BRCA1, BRCA2, ATM, NBN, CHEK2, PALB2, BLM gene mutations in 1000 breast cancer (BC) patients from the Republic of Bashkortostan (RB) are presented. Germline mutations in these genes accounted for 7.5% of breast cancer patients. The wide spectrum of mutations was found in women of Slavic origin, including: c.5266dupC, c.181T>G, and c.4034delA in BRCA1; c.5932G>T in ATM; c.657_661del5 in NBN; c.444+1G>A, c.1100delC, and dele9,10(5kb) in CHEK2; c.509_510delGA and c.172_175delTTGT in PALB2; and c.1642C>T in BLM gene.     

Missense mutations (p.H371Y, p.D438Y) in gene CHEK2 are associated with breast cancer risk in women of Balochistan origin

CHEK2 encodes a serine/threonine-protein kinase which plays a critical role in DNA damage signaling pathways. CHEK2 directly phosphorylates and regulates the functions of p53 and BRCA1. Most women with breast and/or ovarian cancer are not carriers of mutant BRCA1 or BRCA2. Multiple studies have shown that a CHEK2*1100delC confers about a two-fold increased risk of breast cancer in unselected females and a tenfold increase in males. Moreover, studies have shown that first-degree relatives of bilateral breast cancer cases who carried the CHEK2*1100delC allele had an eight-fold increased risk of breast cancer. It has been suggested that CHEK2 functions as a low-penetrance susceptibility gene for cancers and multiplies the risks associated with other gene(s) to increase cancer risk. The main goal of this study was to evaluate and to compare the role of truncating mutations, splice junction mutations and rare missense substitutions in breast cancer susceptibility gene CHEK2. Present study was performed on 140 individuals including 70 breast cancer patients both with and without family history and 70 normal individuals. Written consent was obtained and 3 ml intravenous blood was drawn from all the subjects. DNA was extracted from all the samples through inorganic method published already. Primers were synthesized for all the 14 exons of CHEK2 gene. Coding and adjacent intronic sequences of CHEK2 gene were amplified and sequenced. Two genetic variants (p.H371Y, p.D438Y) were found in exon 10 and exon 11 of gene CHEK2 which were not found in any of the 70 control individuals from same geographical area and ethnic group. The genetic variant c.1312G>T (p.D438Y) identified in a patient with a family history of breast cancer. To our knowledge, this is first mutation scanning study of gene CHEK2 from Balochistan population.     

Analysis of BRCA1/2 and CHEK2 mutations in ovarian cancer and primary multiple tumors involving the ovaries. Patients of Russian population using biochips

Ovarian cancer (OC) is one of the leading cause of cancer death in women. Inherited BRCA1 and BRCA2 mutations strikingly increase OC risk (with lifetime risk estimates ranging at 10-60%). Mutation 1100delC in CHEK2 gene was shown to be associated with breast cancer in women carrying this mutation. Knowledge of the nature and frequency of population-specific mutations in these genes is a critical step in the development of simple and inexpensive diagnostic approaches to DNA analysis. The frequencies of 185delAG, 300T>G, 4153delA, 4158A>G, 5382insC mutations in BRCA1 gene, 695insT and 6174delT mutations in BRCA2 gene and 1100delC mutation in CHEK2 gene were analyzed using biochips in Russian OC patients. We studied 68 women who received a diagnosis of epithelial OC and 19 women with primary multiple tumors involving the ovaries. The 185delAG, 300T>G, 4153delA and 5382insC in BRCA1 gene were identified. The most prevailing mutation was 5382insC in BRCA1 gene (87.5% of all BRCA1 mutations OC patients, 50.0% in patients with primary multiple tumors involving the ovaries). No mutations in BRCA2 and CHEK2 genes were detected.     

Prevalence of mutations BRCA1 5382insC, and CHEK2 1100delC in the population of Siberian region

Frequencies of the 538insC mutation in the BRCA1 gene and the 1100delC mutation in the CHEK2 gene were compared in the group of breast cancer patients and the large-scale sample, consisting of 7920 DNA specimens from healthy residents of the city of Novosibirsk. Higher frequencies of these mutations in the patient group compared to the control sample (1.95 versus 0.25% for BRCA1 5382insC, and 1.78 versus 0.40% for CHEK2 1100delC) were observed, pointing to their association with susceptibility to breast cancer (OR = = 7.86, 95% CI 3.51-17.30 and OR =4.46, 95% C1 2.04-9.49, respectively).     

Abnormal splicing of ABCA1 pre-mRNA in Tangier disease due to a IVS2 +5G>C mutation in ABCA1 gene

Two point mutations of ABCA1 gene were found in a patient with Tangier disease (TD): i) G>C in intron 2 (IVS2 +5G>C) and ii) c.844 C>T in exon 9 (R282X). The IVS2 +5G>C mutation was also found in the brother of another deceased TD patient, but not in 78 controls and 33 subjects with low HDL. The IVS2 +5G>C mutation disrupts ABCA1 pre-mRNA splicing in fibroblasts, leading to three abnormal mRNAs: devoid of exon 2 (Ex2-/mRNA), exon 4 (Ex4-/mRNA), or both these exons (Ex2-/Ex4-/mRNA), each containing a translation initiation site. These mRNAs are expected either not to be translated or generate short peptides. To investigate the in vitro effect of IVS2 +5G>C mutation, we constructed two ABCA1 minigenes encompassing Ex1-Ex3 region, one with wild-type (WTgene) and the other with mutant (MTgene) intron 2. These minigenes were transfected into COS1 and NIH3T3, two cell lines with a different ABCA1 gene expression. In COS1 cells, WTgene pre-mRNA was spliced correctly, while the splicing of MTgene pre-mRNA resulted in Ex2-/mRNA. In NIH3T3, no splicing of MTgene pre-mRNA was observed, whereas WTgene pre-mRNA was spliced correctly. These results stress the complexity of ABCA1 pre-mRNA splicing in the presence of splice site mutations.     

Low Prevalence of CHEK2 Gene Mutations in Multiethnic Cohorts of Breast Cancer Patients in Malaysia

CHEK2 is a protein kinase that is involved in cell-cycle checkpoint control after DNA damage. Germline mutations in CHEK2 gene have been associated with increase in breast cancer risk. The aim of this study is to identify the CHEK2 gene germline mutations among high-risk breast cancer patients and its contribution to the multiethnic population in Malaysia. We screened the entire coding region of CHEK2 gene on 59 high-risk breast cancer patients who tested negative for BRCA1/2 germline mutations from UKM Medical Centre (UKMMC), Hospital Kuala Lumpur (HKL) and Hospital Putrajaya (HPJ). Sequence variants identified were screened further in case-control cohorts consisting of 878 unselected invasive breast cancer patients (180 Malays, 526 Chinese and 172 Indian) and 270 healthy individuals (90 Malays, 90 Chinese and 90 Indian). By screening the entire coding region of the CHEK2 gene, two missense mutations, c.480A>G (p.I160M) and c.538C>T (p.R180C) were identified in two unrelated patients (3.4%). Further screening of these missense mutations on the case-control cohorts unveiled the variant p.I160M in 2/172 (1.1%) Indian cases and 1/90 (1.1%) Indian control, variant p.R180C in 2/526 (0.38%) Chinese cases and 0/90 Chinese control, and in 2/180 (1.1%) of Malay cases and 1/90 (1.1%) of Malay control. The results of this study suggest that CHEK2 mutations are rare among high-risk breast cancer patients and may play a minor contributing role in breast carcinogenesis among Malaysian population.     

LKB1基因多态性与2型糖尿病相关性研究

目的:探讨陕西汉族人群中LKB1基因位点rs741765(380CT)及rs6510599(459GA)单核苷酸多态性(SNPs)与2型糖尿病遗传易感性及相关临床代谢指标的关系。方法:采用等位基因特异性引物PCR(SASP-PCR)对2型糖尿病患者130例及健康对照组100例进行LKB1基因内含子6 rs741765(380CT)及内含子1 rs6510599(459GA)两个位点进行基因多态性筛查,并测序鉴定,分析其基因多态性位点与2型糖尿病临床代谢指标关系。结果:rs741765(380CT)基因突变情况:2型糖尿病患者TT基因型频率显著高于健康对照组(P=0.023);TT基因2型糖尿病组中糖化血红蛋白水平及低密度脂蛋白胆固醇水平在型中明显升高(P=0.030;P=0.002);健康对照组中,空腹血糖水平在TT基因型中明显升高(P=0.011)。rs6510599(459GA)基因突变情况:AA基因型频率在2型糖尿病组及健康对照组间无显著性差异(P0.05);该基因位点与临床指标亦无相关性(P0.05)。结论:陕西汉族人群中LKB1基因内含子6 rs741765(380CT)及内含子1 rs6510599(459GA)存在基因多态性。LKB1基因内含子6 rs741765(380CT)基因多态性与2型糖尿病的发病有相关性。LKB1基因内含子1 rs6510599(459GA)基因多态性与2型糖尿病的发病无相关性。     

The breast cancer susceptibility allele CHEK2*1100delC promotes genomic instability in a knock-in mouse model

Allelic variants of CHEK2 contribute to an elevated risk for human breast cancer and possibly other cancer types. In particular, the CHEK2*1100delC polymorphic variant has been identified as a low-penetrance breast cancer susceptibility allele in breast cancer families with wild type BRCA1 and BRCA2. To better understand the molecular basis by which this allele increases risk for disease, we have generated a mouse in which the wild type CHEK2 (Chk2 in mouse) allele has been replaced with the 1100delC variant. Mouse embryo fibroblasts (MEFs) derived from these mice have an altered cell cycle profile in which a far greater proportion of cells are in S-phase and in G2 (4N) compared with wild type cells. The mutant cells show signs of spontaneous genomic instability as indicated by polyploidy and an increase in DNA double strand breaks.     

GJB2 and mitochondrial A1555G gene mutations in nonsyndromic profound hearing loss and carrier frequencies in healthy individuals

This study aimed to assess mutations in GJB2 gene (connexin 26), as well as A1555G mitochondrial mutation in both the patients with profound genetic nonsyndromic hearing loss and healthy controls. Ninety-five patients with profound hearing loss (>90 dB) and 67 healthy controls were included. All patients had genetic nonsyndromic hearing loss. Molecular analyses were performed for connexin 26 (35delG, M34T, L90P, R184P, delE120, 167delT, 235delC and IVS1+1 A-->G) mutations, and for mitochondrial A1555G mutation. Twenty-two connexin 26 mutations were found in 14.7% of the patients, which were 35delG, R184P, del120E and IVS1+1 A-->G. Mitochondrial A1555G mutation was not encountered. The most common GJB2 gene mutation was 35delG, which was followed by del120E, IVS1+1 A-->G and R184P, and 14.3% of the patients segregated with DFNB1. In consanguineous marriages, the most common mutation was 35delG. The carrier frequency for 35delG mutation was 1.4% in the controls. 35delG and del120E populations, seems the most common connexin 26 mutations that cause genetic nonsyndromic hearing loss in this country. Nonsyndromic hearing loss mostly shows DFNB1 form of segregation.     

Mutation and polymorphism analysis of the human homogentisate 1, 2-dioxygenase gene in alkaptonuria patients.

Alkaptonuria (AKU), a rare hereditary disorder of phenylalanine and tyrosine catabolism, was the first disease to be interpreted as an inborn error of metabolism. AKU patients are deficient for homogentisate 1,2 dioxygenase (HGO); this deficiency causes homogentisic aciduria, ochronosis, and arthritis. We cloned the human HGO gene and characterized two loss-of-function mutations, P230S and V300G, in the HGO gene in AKU patients. Here we report haplotype and mutational analysis of the HGO gene in 29 novel AKU chromosomes. We identified 12 novel mutations: 8 (E42A, W97G, D153G, S189I, I216T, R225H, F227S, and M368V) missense mutations that result in amino acid substitutions at positions conserved in HGO in different species, 1 (F10fs) frameshift mutation, 2 intronic mutations (IVS9-56G-->A, IVS9-17G-->A), and 1 splice-site mutation (IVS5+1G-->T). We also report characterization of five polymorphic sites in HGO and describe the haplotypic associations of alleles at these sites in normal and AKU chromosomes. One of these sites, HGO-3, is a variable dinucleotide repeat; IVS2+35T/A, IVS5+25T/C, and IVS6+46C/A are intronic sites at which single nucleotide substitutions (dimorphisms) have been detected; and c407T/A is a relatively frequent nucleotide substitution in the coding sequence, exon 4, resulting in an amino acid change (H80Q). These data provide insight into the origin and evolution of the various AKU alleles.