Genotypes B and C hepatocellular carcinoma-associated hepatitis B virus pre-S mutants: their detection among F1b and A2 - but not F4 - isolates from Argentina.

Prevalence rates of hepatocellular carcinoma (HCC)-associated hepatitis B virus (HBV) pre-S mutants among most genotypes are still lacking. In this study, viral (sub)genotypes of 70 Argentine nucleotide sequences (33 newly obtained) were determined by phylogenetic analysis, and the presence of such mutants was assessed in the American continent for the first time. Nucleotide substitutions of the pre-S2 start codon were observed in 10% of the HBV/A2 sequences. Ten per cent of the HBV/A2 and 12.5% of the HBV/F1b - but none of HBV/F4 - exhibited a deletion in the pre-S1/pre-S2 region. The contribution of these variants to liver cirrhosis (LC) and/or HCC development among HBV/F and HBV/A isolates deserves further prospective clinical studies.

Cytogenetics in acute lymphoblastic leukemia in Mexican children: an institutional experience.

BACKGROUND: Cytogenetic studies in acute lymphoblastic leukemia (ALL) have identified numerical and structural chromosomal abnormalities related to the disease's pathophysiologic characteristics. These findings correlate with prognosis and response to treatment in ALL patients. The purpose of this study was to define the frequency of chromosomal abnormalities in a group of Mexican children with ALL and to compare these data with those reported in the literature. METHODS: Bone marrow chromosome studies with GTG bands were performed in 150 pediatric patients with ALL who were naive to antileukemic treatment and aged from 5 months to 16 years; the majority was diagnosed as L1. RESULTS: Among 131 patients, 30 (22.9%) karyotypes were normal and the remaining 101 (77.1%) had abnormal karyotypes with numerical and/or structural abnormalities. Among patients with numerical abnormalities, the most frequent karyotypes were hyperdiploidy with 51-65 chromosomes (30 patients) and hyperdiploidy with 47-50 chromosomes (18 patients). Among recurrent, non-random, and primary structural abnormalities, the most frequent was t(9;22), followed by t(1;19). Aberrations involving band 11q23 were not detected, and only one of two patients with L3 had the t(8;14). Of the secondary non-random abnormalities, dup(1q), del(6q), and i(7)(q10) were found. CONCLUSIONS: The frequency and type of chromosomal abnormalities found was comparable to those reported in the literature with similar methodology and pediatric populations; however, the number of cases analyzed should be increased to create a database of Mexican children with ALL, and several patients require molecular analysis to identify chromosomal abnormalities not detected through conventional cytogenetic studies.

Identificación de una nueva anomalía citogenética en el síndrome de duplicación 3q / Identification of a new cytogenetic rearrangement in the duplication 3q syndrome

Se presenta el caso de un paciente masculino con retraso psicomotor y características fenotípicas del síndrome dup (3q). El estudio citogenético reveló un rearreglo cromosómico de novo consistente en una inserción invertida de la región duplicada que resultó en un cariotipo 46,XY, der (3) (pter - q13.3::q27 - q26.1::q13.3 - qter). Esta aberración cromosómica no habria sido descrita previamente en este síndrome

Effect of hydroxyurea and normal plasma on DNA synthesis in lymphocytes from Fanconi anemia patients.

Fanconi anemia (FA) is characterized at the cellular level by a high frequency of spontaneous chromosomal aberrations; crosslinking agents cause an abnormal increase in the frequency of chromosomal damage, and semiconservative DNA synthesis is severely inhibited. Deoxyribonucleotides are needed in both semiconservative and repair DNA synthesis. To investigate the involvement of deoxyribonucleotide pools in the inhibition of DNA synthesis in FA, we evaluated the effect on FA lymphocytes of hydroxyurea (HU), an inhibitor of ribonucleotide reductase which is known to alter the intracellular levels of deoxyribonucleotides. To achieve this goal, lymphocyte cultures of 4 FA patients and 4 normal individuals were used. Cultures were treated with HU and/or mitomycin C and normal human plasma. All cultures were processed to detect the number of DNA synthesizing nuclei by autoradiography. Scoring of 2000 nuclei for each kind of culture every 6 h in the last 24 h of incubation showed that, in long incubation periods, DNA synthesis in FA is largely inhibited by HU and this hypersensitivity may be partially decreased by addition of normal human plasma. It is known that recovery from damage induced by HU involves several enzymes such as flavin oxido-reductase, superoxide dismutase and catalase which are involved in the production or scavenging of O2 radicals; FA cells are deficient in the detoxification of oxygen and this could explain the response of FA cells to HU.

[Detection of aneuploidies using in situ hybridization in cells of the oral mucosa]. / Detección de aneuploidías por hibridación in situ en células de mucosa oral.

Aneuploidies have been traditionally diagnosed by chromosome analysis, however this method may be difficult to perform in certain cellular types or in severely ill patients. With the fluorescence in situ hybridization (FISH) technique it is possible to identify the number of specific chromosomes in interphase cells. In the present study we analyzed exfoliated epithelial cells from the oral mucosa of 15 patients with trisomy 21, and in six patients with mosaicism; five normal subjects were included for comparison. To allow the probe to reach its target DNA we first treated the keratin-surrounded membrane with pepsin during 20 minutes. In the 15 cases of trisomy 21, the cells showed five fluorescent signals indicating the presence of three chromosomes 21 and two 13, while the normal subjects showed four signals. In one girl with Turner syndrome and a karyotype 46,X+mar, the FISH analysis in 1000 cells revealed that the marker derived from chromosome X and there was a mosaicism 45,X/46,X,r(X). In the other patients with mosaicisms, we observed variations in the proportions of cells but the differences were not significant. In conclusion, interphase FISH on buccal cells showed to be a rapid, effective and non-invasive method for the diagnosis of chromosome aberrations, particularly when the cytogenetic study on lymphocytes is difficult to perform.

[Fluorescence in situ hybridization in 6 patients with alterations of chromosome 18 and in 7 with marker chromosomes]. / Hibridación in situ con fluorescencia en seis pacientes con alteraciones del cromosoma 18 y en siete con cromosomas marcadores.

The purpose of the present study was to use the FISH method to establish the origin of chromosome aberrations currently unidentifiable by routine banding procedures. It was done in 13 cases with structurally rearranged chromosomes, seven of them with non-satellited marker chromosomes; in two of the latter an isochromosome 18p was identified which was consistent with a clinical picture of a tetrasomy 18p. FISH with chromosome-specific painting probes showed a deletion 18q in a girl with a cytogenetically balanced t(8;18). Two patients with deletions and two with 18 ring chromosomes were studied using a telomeric probe: both deletions had telomeric integrity and telomeric material was not present in the 18 rings. In a patient with an abnormal chromosome 18, the FISH analysis confirmed a pericentric inversion. We conclude from these results that FISH can provide a rapid and unequivocal cytogenetic diagnosis, which may improve genetic counseling.

[Effects of the addition of conditioned media on the response of Fanconi anemia lymphocytes to mitomycin C]. / Efecto de la adición de medios condicionados sobre la respuesta de los linfocitos de anemia de Fanconi a la mitomicina-C.

It has been shown that the addition of normal plasma to Fanconi anemia (FA) lymphocyte cultures significantly decreases the frequency of mitomycin C (MMC) induced chromosome aberrations, suggesting that normal plasma contains a diffusible correction factor (CF) which is able to partially complement FA lymphocytes. On the other hand, there is evidence suggesting that FA cells are defective in the DNA postreplicative repair. CF could then be involved in DNA repair processes and in possible inducible mechanisms. In the present study MMC-treated FA lymphocytes were grown during the last 24 hours of culture, in conditioned media obtained from untreated and MMC-treated normal cells. The purpose was to investigate if MMC-stressed normal cells were induced to produce CF in vitro. The results failed to show a constant decrease of FA cells chromosome aberrations when plasma-free conditioned media from MMC-stressed normal cells were added (experiments 2 and 3). However, when the conditioned media were supplemented with normal plasma (experiments 1 and 4) a partial repair of MMC-induced damage of the FA cells was observed. The results suggest the presence of CF in normal plasma and two possible mechanisms of action are suggested: CF is involved in DNA repair of MMC-damaged FA cells or it induces cellular division selecting the less damaged cell population through mitosis.

[Effect of gamma radiations on robertsonian translocations]. / Acción de las radiaciones gama sobre las traslocaciones robertsonianas.

Centromeric breaks and the dissociation of Robertsonian translocations have been regarded as the possible cause of a few reported cases of mosaicism. In a previous study we suggested that the dissociative phenomenon is influenced by an instability of the point of fusion, when it is located on a heterochromatic region, which appears to be a preferential mitomycin C (MMC) breakpoint. In this study lymphocytes from 6 robertsonian translocation carriers were treated with gamma rays. In one case who was a mosaic, the MMC induced a statistically significant increase in the number of cells with the dissociation. In the remaining cases, centromeric breaks or complete fissions were observed in 1.8% of the cells. In addition, the analysis of the distribution of breakage points on heterochromatic or euchromatic regions showed that almost 50% of the breaks on translocation chromosomes were located on pericentromeric heterochromatin. We postulate that the dissociation which occurs in robertsonian translocations may be caused by instability of the point of fusion since it is located on a heterochromatic region, susceptible to breakage by clastogenic agents such as MMC and gamma rays.

[Effect of mitomycin C (MMC) on the fusion points of reciprocal translocations]. / Acción de la mitomicina C (MMC) sobre los puntos de fusión de translocaciones recíprocas.

Lymphocytes from five patients having a reciprocal translocation were exposed to MMC to test the stability of the point of reunion which was localized in an euchromatic region. The results showed that the point of fusion in this type of translocations in not a preferential breakpoint. In a patient carrier of a (1;7) translocation, the derivate chromosome showed a significant increased number of breaks compared with the homologous chromosomes. No explanation is available for this finding. Our results support the hypothesis that the observed dissociation of Robertsonian translocation is related to the fact that the point of reunion is located in a heterochromatic region.

[Synergism of bromodeoxyuridine and mitomycin C in the production of chromosomal aberrations in Fanconi's anemia]. / Sinergismo bromodesoxiuridina-mitomicina C en la produccion de aberraciones cromósomicas en anemia de Fanconi.

Synergism of BrdU and MMC on the production of chromosome aberrations in lymphocytes of patients with Fanconi's anemia (FA) was studied. With this purpose, the lymphocytes of an FA patient and of a normal subject were cultured and exposed to BrdU and to MMC in 6 different experiments. The results showed no synergism of these two agents in normal cells. However FA cells exposed to BrdU and MMC showed an increased frequency of aberrations suggesting synergism. Furthermore the chromosome damage produced by MMC was significantly increased by the presence of BrdU in the medium. These results support the hypothesis of a defect of DNA repair in FA cells.

Utilidad de la prueba de exposicion de linfocitos a mitomicina C en el diagnostico de anemia de Fanconi. / Usefulness of the test exposing lymphocytes to mitomycin C in the diagnosis of Fanconi's anemia

Con el objeto de valorar la utilidad de la prueba con MMC en el diagnostico de AF, se estudiaron 3 grupos de individuos: normales, con anemia aplastica con o sin malformaciones esqueleticas y con alteraciones de radio y/o pulgar, pero sin pancitopenia. Los linfocitos de cada individuo se cultivaron con y sin mitomicina C (MMC) para cuantificar el porcentaje de aberraciones cromosomicas espontaneas e inducidas con la MMC, a la cual las celulas de anemia de Fanconi muestran una alta susceptibilidade. Los resultados mostraron en un paciente del grupo con anemia aplastica un porcentaje de aberraciones inducidas 10 veces mayor que los normales y en el grupo de pacientes con alteraciones de radio y/o pulgar, dos de ellos mostraron una respuesta anormalmente elevada a la MMC, con un numero de aberraciones cromosomicas tan alto, que se clasifico como incontable.Con base en estos resultados, y a las caracteristicas clinicas se diagnosticaron 3 casos de anemia de Fanconi y se propone la existencia de heterogeneidad genetica entre ellos

La citogenetica en pediatria: experiencia de 10 anos / Cytogenetics in pediatric practice: a 10 years' experience

Se reviso la experiencia del laboratorio de citogenetica del Instituto Nacional de Pediatria DIF desde el 1o de enero de 1971 hasta el 1o de junio de 1980. Se practico cariotipo con fines diagnosticos a 2,122 probandos y 366 familiares de los mismos. Se encontro anormalidad cromosomica en el 38.1% de los casos indice y en el 13,4% de los familiares.Ademas 18 probandos presentaron inestabilidad cromosomicas entre las primeras la mas frecuente fue la trisomia 21 y entre las segundas la monosomia X. En el trabajo se detallan los cariotipos anormales y se describe su frecuencia en la poblacion estudiada.Al igual que otros estudios similares se demuestra la utilidad de las tecnicas citogeneticas en pediatria