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Biomedical subjects

S N Thibodeau

Publications and source records attributed to S N Thibodeau.

At least 37 records · Page 2Linked to original sources
PubMed2000

Microsatellite instability and hMLH1/hMSH2 expression in young endometrial carcinoma patients: associations with family history and histopathology.

Endometrial cancer is the second most common malignancy in patients with hereditary nonpolyposis colorectal cancer (HNPCC). The age at diagnosis of HNPCC-associated endometrial cancer is approximately 15 years younger than for sporadic endometrial cancer. Our current study was undertaken to determine the frequency of microsatellite instability (MSI) and absence of hMLH1 or hMSH2 protein expression in young patients with endometrial carcinoma and to correlate these findings with histopathologic and clinical features. Endometrial carcinoma from 62 women (23-52 years, median age 46) were assessed for MSI. Twenty-one of the 62 (34%) tumors demonstrated MSI. Of the 21 tumors demonstrating MSI, 12 showed an absence of hMLH1 expression, 4 showed an absence of hMSH2 expression, and 5 demonstrated normal expression of both proteins. All 41 tumors without MSI demonstrated normal hMLH1 and hMSH2 expression. Two patients with MSI tumors fulfilled the Amsterdam criteria for HNPCC, while 2 had histories suggestive of HNPCC. None of the patients with tumors without MSI had a personal or family cancer history suggestive of HNPCC. The MSI phenotype was associated (p < 0.05) with high FIGO stage and grade, cribriform growth pattern, mucinous differentiation and necrosis. Our findings suggest that the frequency of HNPCC in young endometrial cancer patients is relatively low when compared with the frequency of HNPCC in young colorectal cancer patients. Defects of the MMR proteins hMSH2 or hMLH1 account for MSI in most but not all endometrial cancers from young patients.

Adaptor Proteins, Signal Transducing↗
PubMed2000

BRCA1 and BRCA2 have a limited role in familial prostate cancer.

Epidemiological studies have suggested that the breast cancer susceptibility genes, BRCA1 and BRCA2, may be involved in the development of prostate cancer. Several studies have screened prostate cancer populations for the presence of BRCA1 and BRCA2 mutations, with few mutations identified. In this study, 22 high-risk prostate cancer families (at least three cases of prostate cancer) were screened by conformation-sensitive gel electrophoresis (CSGE) for mutations in BRCA1 and BRCA2. To maximize the chance of finding mutations in these two genes, families were also selected for the presence of at least two cases of breast and/or ovarian cancer. We identified one previously reported BRCA2 missense mutation and two previously unreported BRCA2 intron polymorphisms. No BRCA1 or BRCA2 truncating mutations were detected. Thus, BRCA1 and BRCA2 appear to have a limited role in familial prostate cancer, and families with both prostate and breast cancer may result from mutations in other predisposition genes.

Aged↗
PubMed2000

Genetic heterogeneity in Peutz-Jeghers syndrome.

LKB1, the human gene encoding a serine threonine kinase, was recently identified as a susceptibility gene for Peutz-Jeghers syndrome (PJS), a disease characterized by the constellation of intestinal hamartomata, oral mucocutaneous hyperpigmentation, and an increased risk for gastrointestinal as well as extraintestinal malignancies. To date, the majority of individuals with PJS have been found to have genetic alterations in LKB1, most of which result in protein truncation. Additionally, linkage analyses have suggested a modicum of genetic heterogeneity, with the majority of PJS families showing linkage to the LKB1 locus. In this study, we evaluated five kindreds with greater than two affected family members, five PJS probands with only one other affected family member, as well as 23 individuals with sporadic PJS for mutations within the LKB1 gene. Conformation sensitive gel electrophoresis was utilized for the initial screen, followed by direct sequence analysis for characterization. Long-range PCR was used for the detection of larger genetic insertions or deletions. Mutation analysis revealed genetic alterations in LKB1 in two probands who had a family history of PJS. LKB1 mutations were detected in only four of the remaining 23 cases of sporadic PJS. These data suggest the presence of significant genetic heterogeneity for PJS and the involvement of other loci in this syndrome.

AMP-Activated Protein Kinase Kinases↗
PubMed2000

Iron overload in cirrhosis-HFE genotypes and outcome after liver transplantation.

Previously, we found appreciable hepatic iron deposition in one third of our patients undergoing liver transplantation (LTx) with approximately 10% of cases having quantifiable iron in the range of that seen in hereditary hemochromatosis (HHC). The aim of this study was to compare clinical outcome in liver transplant patients with and without iron overload. We also sought to determine the prevalence of HFE mutations in liver transplant patients with iron overload. Of 456 consecutive liver transplants, 41 explants had an hepatic iron index (HII) greater than 1.9, and these cases were compared to 41 matched liver transplant recipients without increased hepatic iron. Posttransplantation complications, along with patient and graft survival were monitored. HFE gene testing was performed using DNA-based techniques. Kaplan-Meier 5-year patient survival after LTx was significantly lower in cases with hepatic iron overload compared to matched controls without iron excess (48% vs. 77%; P =.045). Fatal infections (especially fungal) were more common in patients with iron overload (24% vs. 7%; P =.03). Of the 41 patients with a liver explant HII greater than 1.9, only 4 were C282Y homozygotes. Patients with severe hepatic explant iron overload undergoing LTx have a reduced survival compared to liver transplant recipients without explant iron excess. The reduced survival was attributable mainly to fatal bacterial and fungal infections. Despite the iron overload, HFE gene mutations were uncommon in patients with hepatic explant hemosiderosis.

Female↗
PubMed2000

Higher risk of mismatch repair-deficient colorectal cancer in alpha(1)-antitrypsin deficiency carriers and cigarette smokers.

Microsatellite instability (MSI) is a genomic alteration observed in 15-30% of colorectal cancer (CRC). Two MSI phenotypes have been defined for CRC: MSI-H is characterized by MSI at > or =30% of the examined loci and MSI-L by MSI at 1-30% of the loci. An absence of MSI at any examined loci has been defined as a microsatellite stable (MSS) phenotype. Current data suggest the majority of MSI tumors are the result of defective DNA mismatch repair (MMR). In this study, we have determined the alpha(1)-antitrypsin deficiency carrier (alpha(1)ATD-ht) status of 161 CRC patients whose MSI phenotype and protein expression states had previously been determined. Cases were selected to enrich a larger number of MSI-H cases. Among 51 CRC patients with MSI-H tumors, the alpha(1)ATD-ht rate was 21.6%; among 110 patients with MSI-L/MSS tumors, the rate was 9.1% (MSI-H vs MSI-L/MSS, P = 0.02); and among the 191 population-based controls the alpha(1)ATD-ht rate was 9.4% (MSI-H vs controls, P = 0.02). The estimated relative risk of having MSI-H CRC among alpha(1)ATD-ht was 3.1 after adjusting for age, gender, and smoking history. The risk of having MSI-H CRC among current and past smokers was 6.6 and 2.7, respectively. Patients who were alpha(1)ATD-ht and smoked had a 20-fold increased risk of developing an MSI-H CRC compared to nonsmokers who were homozygous normal at the alpha(1)ATD locus. Our findings suggest an etiologic link between alpha(1)ATD alleles and development of CRC with defective MMR, and a synergistic effect between smoking and alpha(1)ATD allele in the development of MSI-H CRC.

Aged↗
PubMed2000

Isolated supravalvular aortic stenosis: functional haploinsufficiency of the elastin gene as a result of nonsense-mediated decay.

We have used single-strand conformation and heteroduplex analyses of genomic amplimers to identify point mutations within the elastin gene (ELN) in patients with non-syndromic supravalvular aortic stenosis (SVAS) from a total of eight unrelated families. Six novel point mutations were identified. We have collected detailed clinical information on mutation carriers and demonstrated significant non-penetrance in some of the families. Together with the new mutations described here, 14 point mutations have been reported in SVAS patients, and 10 of these result in premature stop codons (PTCs). We have analyzed the expression of ELN alleles in skin fibroblasts from one SVAS patient and shown that PTC mutations indeed result in selective elimination of mutant transcripts. Inhibition of the nonsense-mediated decay mechanism by cycloheximide resulted in the stabilization of mutant elastin mRNA. Allelic inactivation by the ELN mutation in this patient led to an overall decrease of the steady state levels of elastin mRNA. Finally, we have demonstrated reduced synthesis and secretion of tropoelastin by skin fibroblasts from the same SVAS patient. We conclude that PTC mutations in ELN result in nonsense-mediated decay of mutant mRNA in this patient. Given the predominance of PTC mutations in SVAS, we suggest that functional haploinsufficiency may be a pathomechanism underlying most cases of non-syndromic SVAS.

Adolescent↗
PubMed2000

Colorectal cancer screening by detection of altered human DNA in stool: feasibility of a multitarget assay panel.

BACKGROUND & AIMS: Assay of altered DNA exfoliated into stool represents an intriguing approach to screen for colorectal neoplasia, but multiple markers must be targeted because of genetic heterogeneity. We explored the feasibility of a stool assay panel of selected DNA alterations in discriminating subjects with colorectal neoplasia from those without. METHODS: Freezer-archived stools were analyzed in blinded fashion from 22 patients with colorectal cancer, 11 with adenomas > or =1 cm, and 28 with endoscopically normal colons. After isolation of human DNA from stool by sequence-specific hybrid capture, assay targets included point mutations at any of 15 sites on K-ras, p53, and APC genes; Bat-26, a microsatellite instability marker; and highly amplifiable DNA. RESULTS: Analyzable human DNA was recovered from all stools. Sensitivity was 91% (95% confidence interval, 71%-99%) for cancer and 82% (48%-98%) for adenomas > or =1 cm with a specificity of 93% (76%-99%). Excluding K-ras from the panel, sensitivities for cancer were unchanged but decreased slightly for adenomas to 73% (39%-94%), while specificity increased to 100% (88%-100%). CONCLUSIONS: Assay of altered DNA holds promise as a stool screening approach for colorectal neoplasia. Larger clinical investigations are indicated.

Adenocarcinoma↗
PubMed2000

Linkage analyses at the chromosome 1 loci 1q24-25 (HPC1), 1q42.2-43 (PCAP), and 1p36 (CAPB) in families with hereditary prostate cancer.

Recent studies suggest that hereditary prostate cancer (PRCA) is a complex disease, involving multiple susceptibility genes and variable phenotypic expression. Through linkage analysis, potential prostate cancer susceptibility loci have been mapped to 3 regions on chromosome 1. To investigate the reported linkage to these regions, we conducted linkage studies on 144 PRCA families by using microsatellite markers in regions 1q24-25 (HPC1) and 1q42.2-43 (PCAP). We also examined the 1p36 (CAPB) region in 13 PRCA families with at least one case of brain cancer. No significant evidence of linkage to the HPC1 or PCAP region was found when the entire data set was analyzed. However, weak evidence for linkage to HPC1 was observed in the subset of families with male-to-male transmission (n=102; maximum multipoint nonparametric linkage [NPL] 1.99, P=.03). Weak evidence for linkage with heterogeneity within this subset was also observed (HLOD 1.21, P=.02), with approximately 20% of families linked. Although not statistically significant, suggestive evidence for linkage to PCAP was observed for the families (n=21) that met the three criteria of male-to-male transmission, average age of diagnosis <66 years, and >/=5 affected individuals (maximum multipoint NPL 1.45, P=.08). There was no evidence for linkage to CAPB in the brain cancer-prostate cancer subset. These results strengthen the argument that prostate cancer is a heterogeneous disease and that multiple genetic and environmental factors may be important for its etiology.

Aged↗
PubMed2000

Association of Peutz-Jeghers-like mucocutaneous pigmentation with breast and gynecologic carcinomas in women.

Most reports describe an increased risk of malignancy in Peutz-Jeghers syndrome (PJS). We identified individuals with PJS-like pigmentation but no polyposis, designated as isolated mucocutaneous melanotic pigmentation (IMMP), and 1) characterized their clinical features, 2) assessed them for cancer events, and 3) screened a sample of these subjects for mutations in LKB1, a gene responsible for a portion of PJS cases. Review of Mayo Clinic records from 1945 to 1996 identified 26 patients with IMMP. All were then interviewed or their medical records reviewed to determine if cancer had developed. Conformation-sensitive gel electrophoresis (CSGE) screening for LKB1 mutations was followed by direct sequencing. Ten of these 26 individuals (38%) developed 12 malignancies that arose in the cervix (n = 3), endometrium (n = 3), breast (n = 1), kidney (n = 1), lung (n = 2), colon (n = 1), and lymphatic tissue (n = 1). In females with IMMP, the relative risk for cancer was 3.2 (95% CI, 1.2-6.9), while that for males was not increased. The relative risk for breast and gynecologic cancers was 7.8 (95% CI, 2.5-18.1) in affected females. Of 9 individuals tested, no LKB1 mutations were detected. Classical PJS is associated with an increased cancer risk. Our results indicate that IMMP is another lentiginosis with cancer predisposition. In particular, the relative risk for cancer in females with IMMP was significantly increased, as is true in females with PJS. However, LKB1 mutations did not contribute to the development of IMMP in the patients tested.

Adult↗
PubMed2000

Prevalence and clinical significance of HFE gene mutations in patients with iron overload.

OBJECTIVE: The HFE gene contains two mutant alleles; C282Y and H63D. The C282Y mutation occurs in 55-100% of patients with hereditary hemochromatosis. The aim of our study was to re-examine the frequencies of the C282Y and H63D mutations in patients with mild and marked iron overload and in normal subjects. METHODS: A total of 82 patients with iron overload were included in this study and had hepatic iron index determination and/or quantitation of iron stores by phlebotomy. The control group consisted of 81 healthy blood donors. HFE mutation analysis was performed on leukocyte DNA using PCR-amplified genomic DNA. RESULTS: Of patients with iron overload, 70/82 (85%) were homozygous for C282Y versus 2/81 (2.5%) in the control population. Four patients had no HFE mutations despite significant iron overload, including a sister and brother (brother not included in the study group) with hepatic iron concentrations >500 micromoles/g dry weight. CONCLUSIONS: In all, 85% of our patients with iron overload were C282Y homozygotes, although a few had no HFE gene mutations. Pooled data and analysis of chromosomes considered to be at risk for H63D indicate that H63D is associated with iron overload.

Aged↗
PubMed2000

Differential expression and allelotyping of the p73 gene in neuroblastoma.

p73 has recently been identified as a candidate imprinted tumor suppressor gene in neuroblastoma. To determine the possible involvement of this gene in the pathogenesis of neuroblastoma, we analyzed allelic expression, screened for mutations and determined MYCN copy numbers in 31 primary neuroblastoma tumor samples. Interestingly, the gene was biallelically expressed in 50% (4/8) of informative neuroblastomas, which suggests that activation of the normally silenced allele of this gene plays an important role in the tumorigenesis of neuroblastoma. However, no tumor-specific mutations were identified although 15 polymorphisms were detected in this gene. We also detected a very strong association between a C91T polymorphism and MYCN copy number in this tumor. The T allele was detected in 8/17 (47%) neuroblastomas without MYCN amplifications but not detected in cases with MYCN amplifications (0/14). The biological significance of this association, however, is unknown. Overall the data suggest that p73 may play an important role in the pathogenesis of neuroblastoma but that the true tumor suppressor gene localized to this area still remains to be identified.

Alleles↗
PubMed1999

Identification of the molecular genetic defect of patients with methemoglobin M-Kankakee (M-Iwate), alpha87 (F8) His --> Tyr: evidence for an electrostatic model of alphaM hemoglobin assembly.

We determined that the molecular defect of 2 patients with hemoglobin (Hb) M-Kankakee [Hb M-Iwate, alpha87 (F8) His --> Tyr] resides in the alpha1-globin gene. The proportion of Hb M observed is higher than that predicted for an alpha1-globin variant. Our evidence suggests that the greater-than-expected proportion of Hb M-Kankakee results from preferential association of the electronegative beta-globin chains with the alpha(M)-globin chains that are more electropositive than normal alpha-globin chains.

Female↗
PubMed1999

Microsatellite instability and 8p allelic imbalance in stage B2 and C colorectal cancers.

BACKGROUND: Microsatellite instability (MSI) and allelic imbalance involving chromosome arms 5q, 8p, 17p, and 18q are genetic alterations commonly found in colorectal cancer. We investigated whether the presence or absence of these genetic alterations would allow stratification of patients with Astler-Coller stage B2 or C colorectal cancer into favorable and unfavorable prognostic groups. METHODS: Tumors from 508 patients were evaluated for MSI and allelic imbalance by use of 11 microsatellite markers located on chromosome arms 5q, 8p, 15q, 17p, and 18q. Genetic alterations involving each of these markers were examined for associations with survival and disease recurrence. All P values are two-sided. RESULTS: In univariate analyses, high MSI (MSI-H), i.e., MSI at 30% or more of the loci examined, was associated with improved survival (P =.02) and time to recurrence (P =.01). The group of patients whose tumors exhibited allelic imbalance at chromosome 8p had decreased survival (P =.02) and time to recurrence (P =.004). No statistically significant associations with survival or time to recurrence were observed for markers on chromosome arms 5q, 15q, 17p, or 18q. In multivariate analyses, MSI-H was an independent predictor of improved survival (hazard ratio [HR] = 0.51; 95% confidence interval [CI] = 0.31-0.82; P =.006) and time to recurrence (HR = 0.42; 95% CI = 0.24-0.74; P =.003), and 8p allelic imbalance was an independent predictor of decreased survival (HR = 1.89; 95% CI = 1.25-2.83; P =. 002) and time to recurrence (HR = 2.07; 95% CI = 1.32-3.25; P =.002). CONCLUSIONS: Patients whose tumors exhibited MSI-H had a favorable prognosis, whereas those with 8p allelic imbalance had a poor prognosis; both alterations served as independent prognostic factors. To our knowledge, this is the first report of an association between 8p allelic imbalance and survival in patients with colorectal cancer.

Adult↗
PubMed1999

Preclinical memory decline in cognitively normal apolipoprotein E-epsilon4 homozygotes.

OBJECTIVE: To determine, in a cross-sectional evaluation of nondemented individuals, if age-related memory decline is influenced by apolipoprotein E (apoE) genotype. BACKGROUND: The apoE-4 allele is an important risk factor for AD. PET in cognitively normal apoE-4 carriers (mean age, 56 years) shows reduced cerebral metabolism suggestive of very early AD that precedes clinically evident memory loss or MRI-based hippocampal atrophy. METHODS: Tests of immediate and delayed recall (primary outcome measures) and other neuropsychological measures (secondary outcome measures) were given to three genetically defined groups of cognitively normal individuals (age, 49 to 69 years) including apoE-4 homozygotes (n = 25), apoE-4 heterozygotes (n = 25, all epsilon3/4), and apoE-4 noncarriers (n = 50). Groups were matched for age, gender, and educational background. Cross-sectional comparisons between the genetic subgroups of the relationship between age and test score were performed for each neuropsychological measure. RESULTS: There were no intergroup differences in mean scores on any neuropsychological measure, but tests sensitive to immediate and delayed recall showed a significant negative correlation with age in the apoE-4 homozygote group relative to the noncarrier group. CONCLUSION: Consistent with previous neuropsychological studies of early AD, this cross-sectional study suggests that age-related memory decline occurs earlier in cognitively healthy apoE-4 homozygotes than in apoE-4 heterozygotes and noncarriers, and precedes clinically detectable AD.

Age Factors↗
PubMed1999

Supravalvular aortic stenosis: a splice site mutation within the elastin gene results in reduced expression of two aberrantly spliced transcripts.

We have screened the elastin gene for mutations responsible for supravalvular aortic stenosis (SVAS) in two large, independently collected families with isolated (nonsyndromic) SVAS. By single-strand conformation polymorphism and heteroduplex analysis, we have identified a C to G transversion within the acceptor splice site of exon 16 in SVAS patients from both families. This mutation segregates in both families with high penetrance of SVAS, and all affected individuals carry the mutation. Haplotype analysis by using closely linked polymorphisms, including a previously unreported BfaI restriction fragment length polymorphism within the 3'-UTR of the elastin gene, indicates that the mutations found in the two apparently non-overlapping kindreds are identical by descent. To study the effect of the mutation on the expression of the mutant allele, we have established a primary skin fibroblast culture from one of the affected individuals. Reverse transcription/polymerase chain reaction analysis of elastin mRNA species indicates that the mutation results in two abnormal elastin mRNA species. One mutant elastin mRNA is generated by the activation of a cryptic splice site that lies within intron 15 and that adds 44 bp of intronic sequence to the sequence encoded by exon 16. This insertion creates a frame shift that results in a 59-amino-acid-long abnormal protein sequence and leads to a termination codon in the mRNA sequence encoded by exon 17. The smaller abnormal mRNA species arises as a consequence of the skipping of exon 16. This study demonstrates, for the first time, the expression of mutant alleles of the elastin gene in patients with isolated SVAS.

Alternative Splicing↗
PubMed1999

Origin of microsatellite instability in gastric cancer.

Microsatellite instability (MSI) is observed in 13-44% of gastric carcinoma. The etiology of MSI in gastric carcinoma has not been clearly defined. To assess the role of mismatch repair in the development of MSI in gastric cancer, expression of hMSH2 and hMLH1 was explored. We examined 117 gastric carcinomas for MSI and observed instability at one or more loci in 19 (16%) of these tumors. Of the 19 tumors with MSI, nine exhibited low-rate MSI (MSI-L) with instability at <17% of loci, whereas the remaining 10 exhibited high-rate MSI (MSI-H) with instability at >33% of loci examined. Immunohistochemical staining for hMLH1 and hMSH2 was performed on eight of the tumors with MSI-H, five with MSI-L, and 15 tumors without MSI. All eight tumors with MSI-H showed loss of staining for either hMLH1 (n = 5) or hMSH2 (n = 3). In contrast, tumors with MSI-L or without MSI all showed normal hMSH2 and hMLH1 protein expression patterns. Moreover, all eight of the tumors with MSI-H also showed instability at BAT-26, whereas none of the MSI-L tumors or tumors without instability showed instability at BAT-26. These findings suggest that the majority of high-level MSI in gastric cancer is associated with defects of the mismatch repair pathway. Although larger studies are needed, BAT-26 appears to be a sensitive and specific marker for the MSI-H phenotype in gastric carcinoma.

Adaptor Proteins, Signal Transducing↗