Biomedical subjects

M Robledo

Publications and source records attributed to M Robledo.

At least 37 records · Page 2Linked to original sources

PubMed1999

High prevalence of the C634Y mutation in the RET proto-oncogene in MEN 2A families in Spain.

The RET proto-oncogene encodes a receptor tyrosine kinase expressed in neural crest derived tissues. Germline mutations in the RET proto-oncogene are responsible for three different dominantly inherited cancer syndromes: multiple endocrine neoplasia type 2A (MEN 2A), type 2B (MEN 2B), and familial medullary thyroid carcinoma (FMTC). MTC can also occur sporadically. Molecular characterisation of the RET proto-oncogene has been performed by PCR-SSCP analysis, direct DNA sequencing, and restriction enzyme analysis in 49 unrelated, Spanish, MEN 2 families: 30 MEN 2A families, six FMTC families, and 13 families classified as "other". Germline missense mutations in one of six cysteine codons (609, 611, 618, and 620 in exon 10, and codons 630 and 634 in exon 11), which encode part of the extracellular cysteine rich domain of RET, have been detected in the majority of these families: 100% of MEN 2A families, 67% of FMTC families, and 54% of families classified as "other". No RET mutations in exons 10, 11, 13, 14, 15, or 16 were detected in the remaining families. The most frequent RET mutation in MEN 2A Spanish families is C634Y, occurring in 73% of cases. Haplotype analysis does not exclude the possibility of founder effects in Spanish MEN 2A families with the C634Y mutation.

Chromosomes, Human, Pair 1↗

PubMed1998

Molecular analysis of the six most recurrent mutations in the BRCA1 gene in 87 Spanish breast/ovarian cancer families.

BRCA1 accounts for nearly all families with multiple cases of both early onset breast and ovarian cancer and about 45% of families with breast cancer only. Although to date more than 200 distinct mutations have been described, several have been found to be recurrent in the gene. We have analyzed 87 Spanish breast/ovarian cancer families for the six most recurrent mutations in the BRCA1 gene. The analysis of the five exons where these mutations are located was made using the SSCP and sequenciation techniques. Four mutations were found in our families and only two carried one of the six mutations analyzed. In both cases the mutation identified was 185delAG. Our results suggest that these six mutations are not specially recurrent in the Spanish population and that differences in the geographical origin of the families can influence the type and proportion of mutations identified.

Adult↗

PubMed1998

Hypermethylation of p15/ink4b/MTS2 gene is differentially implicated among non-Hodgkin's lymphomas.

P15 (MTS2) gene is a candidate tumor suppressor gene localized adjacent to the p16 gene at 9p21. Deletions at the 9p21 region frequently affect both p16 and p15 genes, however, mutations in the coding sequence of the p15 gene have not been found in the majority of tumors analyzed, including non-Hodgkin's lymphomas. Abnormal methylation of the promoter region of p15 has been recently described as an alternative mechanism of inactivation of this gene. We analyzed 72 non-Hodgkin's lymphomas (NHL) for methylation at p15 exon 1 by PCR and Southern blot techniques using methylation-sensitive restriction enzymes. Abnormal methylation was found in eight cases (11%), most of them (three MALT, one anaplastic T cell lymphoma, one Burkitt and one follicular lymphoma) showing hypermethylation in the p16 gene also. In contrast, two pleomorphic T cell NHL showed a selective methylation at p15 gene, while the p16 gene remained unmethylated. The results show that methylation at the p15 gene is frequently associated with p16 methylation in NHL, and suggest that selective methylation of p15, although uncommon, could be a specific alteration implicated in T cell NHL.

Carrier Proteins↗

PubMed1998

Molecular analysis of the BRCA2 gene in 16 breast/ovarian cancer Spanish families.

The recent isolated gene BRCA2 is responsible for about 45% of familial breast cancer and the majority of male breast cancer families. In order to evaluate the role of inherited BRCA2 mutations in Spanish families, the complete coding sequence of the gene was screened by SSCP/sequencing in 16 high-risk breast/ovarian cancer families. Four mutations were found that cause a premature termination codon. Two of them have been reported elsewhere and one is a novel mutation. In addition we have found seven polymorphisms, two of which have not been previously described. One of the mutations, 936delAAAC was found in two of our high-risk families. Because this mutation is considered as recurrent, we have tried to estimate its frequency in our breast cancer population. A total of 127 moderate- high-risk families were screened for this mutation and it was also found in another high-risk family. All the families carrying the 936delAAAC mutation harboured part of a common haplotype shared by other reported carriers, suggesting a possible founder effect for this mutation.

Adult↗

PubMed1997

Mutation analysis of the BRCA2 gene in breast/ovarian cancer Spanish families: identification of two new mutations.

The recently isolated gene BRCA2 is responsible for about 45% of familial breast cancer and the majority of male breast cancer families. We have screened 12 high risk breast/ovarian Spanish families for mutations in BRCA2, using SSCP followed by direct sequencing. We have found mutations in four of our 12 families (33.3%), including two with male breast cancer. Three of the mutations were frameshift and one was a missense. Two of the mutations have been previously published and two are new mutations.

Adult↗

PubMed1997

Frequent allelic losses of 9p21 markers and low incidence of mutations at p16(CDKN2) gene in non-Hodgkin lymphomas of B-cell lineage.

We present an allelotype analysis of 35 cases of non-Hodgkin lymphomas and normal pairs using four microsatellite markers that flank the region occupied by the CDKN2 gene locus at 9p21. Frequent allelic losses (LOH) were detected in B-cell lineage NHLs, including Burkitt lymphoma (33.3% of total, if we only consider high grade tumors). In five of these tumors LOH did not include the CDKN2 gene. Mutational analysis of exon 1 and 2 of CDKN2 (SSGP and sequencing of abnormal bands) revealed a nonsense mutation (Arg72Ter) in one tumor (case 10), where the second hit of the Knudson's model consisted of the elimination of the wild type allele. In view of these results, the hypothesis of two different candidate tumor suppressor gene regions around the CDKN2 locus remains an intriguing possibility.

Alleles↗

PubMed1997

A region of allelic imbalance in 1q31-32 in primary breast cancer coincides with a recombination hot spot.

Previous studies have shown that the 1q31-32 region frequently presents allelic imbalance (AI) in various neoplastic diseases, such as breast cancer, medulloblastoma, male germ cell tumors, and renal collecting duct carcinoma, suggesting the presence of a tumor suppressor gene in this location. We used 19 informative microsatellite markers to analyze 33 primary breast tumors for AI in the 1q31-32 region. Our results demonstrate a 10-cM critical region of AI that is present in more than 60% of the tumors. This region is located proximal to the REN locus and is flanked by the CACNL1A3 and D1S2655 markers. Most important, the critical region of AI coincides with a female hot spot of recombination, suggesting a possible correlation between the two regions.

Alleles↗

PubMed1997

[A clinical, cytogenetic and molecular study of 10 patients with the Prader-Willi syndrome].

BACKGROUND: The Prader-Willi syndrome (PWS) is a neurogenetic disorder associated with abnormalities in the chromosomal region 15q11-13 of paternal origin. Most cases (65-85%) have a deletion involving the paternally derived chromosome and the remainder (20-25%) have a maternal uniparental disomy. Some patients have a defect in the imprinting process. We report the results of molecular, cytogenetic and clinical studies on 10 PWS patients. PATIENTS AND METHODS: 18 suspected patients were classified as PWS typical or not typical as they fulfilled or not the clinical criteria for PWS. Cytogenic studies-high resolution chromosome banding analyses (HRGTG) and fluorescence in situ hybridization (FISH) -and molecular chromosome genetic analyses--microsatellite markers and Southern blotting--were carried out from peripheral blood lymphocytes. RESULTS: PWS was confirmed in 10 probands. 8 fulfilled the clinical criteria for PWS and showed cytogenetic and/or molecular abnormalities. In 2 patients without clinical or cytogenetic data, diagnosis was confirmed by molecular methods only. Cytogenetic and molecular findings describe a characteristic clinical picture of PWS. CONCLUSIONS: Cytogenetic techniques (FISH and HRGTG) confirmed PWS diagnosis in 40% of cases, microsatellite studies in 70% of them and Southern blotting (the metilation test) in 100% cases. Southern blotting is the method of choice for rapid diagnostic testing of patients suspected of having PWS.

Adolescent↗

PubMed1997

Correlation between mutations in p53 gene and protein expression in human lymphomas.

A discordance between p53 protein overexpression and the presence of mutations in the gene has been observed in many types of tumors, including human lymphomas. To probe this finding, we have studied a large series of 94 lymphomas of different pathologic types and histologic differentiation. Analyzing exons 5-9, we have found mutations in the p53 gene in 7 of 94 cases distributed in different subtypes: 4/12 (33%) high-grade B-cell non-Hodgkin's lymphomas (B-NHLs), in 1 of 5 (20%) high-grade mucosa-associated lymphomas (MALT), in 1 of 22 (4.5%) anaplastic large cell lymphoma (ALCL), and in 1 of 24 (4%) T-cell NHLs. Immunostaining with anti-p53 antibody DO-7 was possible in 87 lymphomas, and overexpression of p53 protein was observed in 16 cases (18%). A discrepancy between the results of SSCP and immunostaining was detected on 18 tumor samples. Two cases with mutations in the gene showed no altered protein expression and 16 cases overexpressed p53 protein had no point mutations. In these cases, the possibility that mutations occur outside the exons studied has been tested and the entire coding sequence analyzed. Only one case showed a mutation in exon 10, and we found two cases carrying a polymorphism in exon 4 and in intron 10. We conclude that mutations in p53 occur mainly in high-grade B-cell NHLs. Although not limited to a specific subtype of lymphoma, they may be rare in Hodgkin's disease and in low-grade lymphomas. The discrepancies between overexpression and presence of mutations suggest (1) the existence of another mechanism to stabilize the p53 protein, and (2) that the immunohistochemistry cannot be used to predict mutations in the gene.

Antibodies, Monoclonal↗

PubMed1997

A high-resolution map of the regulator of the complement activation gene cluster on 1q32 that integrates new genes and markers.

Sixteen microsatellite markers, including two described here, were used to construct a high-resolution map of the 1q32 region encompassing the regulator of the complement activation (RCA) gene cluster. The RCA genes are a group of related genes coding for plasma and membrane associated proteins that collectively control activation of the complement component C3. We provide here the location of two new genes within the RCA gene cluster. These genes are PFKFB2 that maps 15 kilobases (kb) upstream of the C4BPB gene, and a gene located 4 kb downstream of C4BPA, which seems to code for the 72 000 Mr component of the signal recognition particle (SRP72). Neither of these two genes is related structurally or functionally to the RCA genes. In addition, our map shows the centromere-telomere orientation of the C4BPB/MCP linkage group, which is: centromere-PFKFB2-C4BPB-C4BPA-SRP72-C4BPAL1++ +-C4BPAL2-telomere, and outlines an interval with a significant female-male recombination difference which suggests the presence of a female-specific hotspot(s) of recombination.

Chromosome Mapping↗

PubMed1997

Detection of trisomy 8 using conventional cytogenetic techniques and interphase FISH analysis in 34 myeloid disorders: a comparative study.

Trisomy for chromosome 8 is one of the most common chromosome abnormalities detected in myeloid disorders. However, and despite its great incidence, its biologic significance remains poorly understood. Recently, some reports have shown the existence of masked trisomy 8 in myeloid disorders. To try to detect occult trisomy 8, we performed a study in which 34 myeloid disorders with apparent normal karyotypes using conventional cytogenetic techniques were analyzed using fluorescence in situ hybridization (FISH) analysis. Masked trisomy 8 was not detected in any of the 34 cases studied. This suggests that trisomy 8 may be a rare event in myeloid disorders in which an optimal conventional cytogenetic analysis has been performed. The acquisition of trisomy 8 either in early neoplastic stages in some cases or in late neoplastic stages in others and the absence of masked trisomy 8 suggest that this chromosome alteration may not be essential to the development of myeloid disorders.

Bone Marrow↗

PubMed1997

Cytogenetic and molecular studies of siblings with ataxia telangiectasia followed for 7 years.

We present cytogenetic, immunologic, and molecular data obtained over 7 years from a family with ataxia telangiectasia (AT) including 2 affected children and their unaffected sibling, and their obligate heterozygous parents. In a period of 3 years, the T lymphocytes from both AT patients showed clonal rearrangements of chromosomes 7 and 14 at specific bands (7p13, 7q35, 14q12, and 14q32), where loci for the Ig and TCH genes are located. A molecular study was carried out on peripheral blood and bone marrow samples from both patients using Southern blot and PCR for Ig and TCR genes. A monoclonal population for TCR gamma was observed in one of the two affected children, but only in peripheral blood.

Adolescent↗

PubMed1997

Hypermethylation of a 5' CpG island of p16 is a frequent event in non-Hodgkin's lymphoma.

Hypermethylation of a 5' CpG island of p16 gene has been recently described as a possible way of inactivation of this tumor suppressor gene, alternative to deletions and mutations. We have investigated if hypermethylation of a 5' CpG island of p16 occurs in non-Hodgkin's lymphoma (NHL) and normal lymphoid tissue. A total of 82 NHLs were examined for p16 methylation by Southern blot and PCR analysis. Hypermethylation was detected in approximately 20% of B cell lymphomas of both low and high grade and in 15% of T cell NHL. The highest rate of p16 gene methylation in tumors was found among MALT (mucosa-associated lymphoid tissue) lymphomas in which the percentage of cases with p16 gene methylation reached 67%. However, normal lymphoid tissue was always unmethylated at p16 locus. These results indicate that p16 gene methylation is a frequent event in NHLs, mainly in MALT lymphomas, and suggest that it could be an important mechanism of inactivation of this gene.

Binding Sites↗

PubMed1997

The 12 base pair duplication/insertion alteration could be a regulatory mutation.

A wide array of mutations now numbering more than 200 have been identified in the BRCA1 gene, one of the two breast cancer susceptibility genes identified so far. In addition, there have been several variants described but it is not known if they really represent functionally significant mutations of the BRCA1 gene. We report evidence to show that the duplication/ insertion of 12 base pairs in intron 20 could have a real effect on expression of the BRCA1 gene, although it was also present in 1% of our control population.

Adult↗

PubMed1997

[Detection of t(15;17) using cytogenetic, fluorescent in situ hybridization, and molecular techniques. Comparative study of 11 patients with acute promyelocytic leukemia].

OBJECTIVES: Analysis and comparison of the sensitivity for the detection of t(15; 17) with conventional cytogenetic (CC), Southern blotting (SB), metaphase fluorescence in situ hybridization (M-FISH), interphase fluorescence in situ hybridization (I-FISH) and polymerase chain reaction (PCR) techniques. PATIENTS AND METHODS: 11 acute promyelocytic leukaemia (APL) patients (9 M3 and 2 M3v) were studied at diagnosis and partial remission and analyzed with CC (11 cases), SB (7 cases), I-FISH (2 cases) and PCR (3 cases) techniques. RESULTS: The percentages of detection of t(15;17) were: 90.9% (CC), 71.4% (SB), 85.7% (M-FISH) and 100% (I-FISH and PCR). Additional chromosomal abnormalities were detected in 2 cases with CC techniques. CONCLUSIONS: 1.- There is a very good correlation in the detection of t(15; 17) between the techniques analyzed. 2.- At diagnosis, partial remission and relapse, M-FISH and PCR provide a reliable diagnosis of t(15; 17). Nevertheless, it is important to perform a CC analysis because it enables the recognition of additional chromosome abnormalities with putative prognostic importance. 3.- At complete remission, I-FISH and PCR provide a rapid and safe screening of putative residual cells. 4.- The great sensibility of the techniques available for the detection of t(15; 17) translocation allows the use in each laboratory of the most appropriate techniques according to their substructure and the patients' clinical stage.

Chromosomes, Human, Pair 15↗

PubMed1996

Novel rhodopsin mutation in an autosomal dominant retinitis pigmentosa family: phenotypic variation in both heterozygote and homozygote Val137Met mutant patients.

A family affected with autosomal dominant retinitis pigmentosa (RP) is presented. Two clinically affected patients (mother and daughter) were heterozygous for the same novel missense mutation (Val137Met) of the rhodopsin gene (RHO). Both heterozygous and homozygous cases were observed among their few symptomatic relatives. Wide clinical variation was exhibited among the individuals with mutations in this family. None of the controls showed this change in RHO, nor has it been previously reported in other RP families. No other RHO mutation was observed. Additional genetic or environmental factors could play a role in modulating the penetrance and clinical expression of this RHO mutation.

Base Sequence↗

PubMed1996

Incidence of homogeneously staining regions in non-Hodgkin lymphomas.

We report a series of 86 non-Hodgkin's lymphomas (NHL) studied cytogenetically in which two cases with a homogeneously staining region (HSR) located on chromosome 19 and on chromosome 1, respectively, were observed. The low incidence detected (2.3%) suggests that HSR are rare events in NHL. An oncogenetic amplification study was performed with probes for genes that are currently known to undergo amplification and with probes for two genes located on chromosome 19q (AKT2 and BCL-3). We detected no amplification except for AKT2 putative oncogene in the lymphoma in which the HSR was located on chromosome 19. Because amplification of AKT2 putative oncogene has been detected in ovarian carcinomas bearing HSR and in this case NHL, we believe that this gene may be implicated in the pathogenesis of other neoplasias in cooperation with other genes. Further investigation is needed to confirm the low incidence of HSR in NHL and the origin of the amplified material.

Adult↗

PubMed1996

Rearrangement of one RAR-alpha gene in an acute promyelocytic leukemia case with t(15;17) and t(6;17) involving chromosomes 17 band q21.

Acute promyelocytic leukemia (APL) is a specific type of acute myelogenous leukemia characterized by a typical morphology and by a translocation between chromosomes 15 and 17, t(15;17)(q22;q21). Because this translocation is not found in other subtypes of acute myelogenous leukemias, it has become an important marker in the diagnosis and treatment of APL. Here we report a case with apparent absence of t(15;17) cells by cytogenetic techniques at diagnosis. At relapse, a metaphase FISH analysis (not dependent on chromosomal quality), followed by G-banding, was performed. t(15;17) was detected in 60% of the metaphases. In 30% of metaphases, an additional t(6;17) was detected involving the other chromosome 17 at band q21. In parallel, a molecular study (using the Southern blotting technique) was carried out and a single molecular rearrangement of the RAR-alpha gene was detected implying that RAR-alpha was not rearranged in the t(6;17) translocation.

Adult↗