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L Zahed

Publications and source records attributed to L Zahed.

34 records · Page 2Linked to original sources
PubMed1993

Comparison of mouse Y-chromosomal repetitive sequences isolated from Mus musculus, M. spicilegus, and M. spretus.

The mouse Y chromosome is rich in repetitive sequences. We describe a new highly male-specific BALB/c mouse sequence named 142-5. The distribution of 142-5 related sequences, which appeared to be repeated at least 100 times in the male genome of Mus musculus, was visualized on the Y chromosome by in situ hybridization. Their accumulation patterns in the genus Mus showed that the sequences evolved quickly and suggested that they might prove useful for detecting genetic differences between closely related species. To test this hypothesis, we isolated 20 additional sequences from three mouse species (M. musculus, M. spicilegus, and M. spretus) and compared their nucleotide sequences using three different computer programs. It was found that the sequences were remarkably similar but could be divided into four subgroups, and that each species had a distinct set or sets of sequences that were amplified in the Y chromosome.

Animals↗
PubMed1992

In situ hybridization studies for the detection of common aneuploidies in CVS.

We have attempted to evaluate the efficiency of interphase cytogenetics in the detection of specific aneuploidies in chorionic villus samples. For this purpose, we used alphoid repetitive sequences specific for the chromosomes involved in the common aneuploidies, namely probes for chromosomes 13, 18, 21, X, and Y. These probes were applied to normal and abnormal CVS cases, as well as to a few mosaic cases. Results from these preliminary studies indicate that the technique can be very efficient for the detection of specific aneuploidies and can be particularly useful in the analysis of mosaic cases, which usually requires the screening of a high number of metaphases.

Aneuploidy↗
PubMed1992

Cloning of six new genes with zinc finger motifs mapping to short and long arms of human acrocentric chromosome 22 (p and q11.2).

Zinc finger genes encode proteins containing tandemly repeated zinc-mediated folded structures that are found in several transcriptional regulatory proteins. To identify new zinc finger genes, we have screened at low stringency human cosmid libraries enriched in chromosome 22 sequences with a probe derived from the finger region of the mouse Kruppel-like gene, mKr2. We identified 23 nonoverlapping human cosmids cross-hybridizing with the probe. All sequences obtained from cosmid subclones hybridizing with the probe revealed Kruppel-type consensus sequences. Hybridizations to somatic cell hybrid panels and to metaphase chromosomes revealed that 2 nonoverlapping zinc finger cosmids map to chromosome 22p and 4 map to 22q11.2. The 17 other nonoverlapping cosmids most likely map to other chromosomes. The short arms of acrocentric chromosomes are thought to encode only ribosomal RNA genes. Therefore, the identification of two zinc finger genes on chromosome 22p represents an unexpected finding of unknown significance. The four zinc finger genes that map to 22q11.2 are within the cat eye and DiGeorge syndrome regions and thus provide us with potential candidate genes for these developmental malformations.

Amino Acid Sequence↗
PubMed1992

Molecular characterization of a mouse Y chromosomal repetitive sequence that detects transcripts in the testis.

145SC5 is a Y chromosomal repetitive sequence isolated from a BALB/c mouse and is unique in that it detects poly(A)-containing transcripts in the testis. We determined nucleotide sequences of 145SC5 and a related cDNA clone designated PC11 and compared their sequences to that of pYMT2/B, another related cDNA clone. 145SC5 and PC11 are almost identical (97%), while PC11 and pYMT2/B share 84% identity. In situ hybridization and Southern blot analysis with XXSxr male mice demonstrated that 145SC5-related sequences were distributed over the entire length of the Y chromosome including the short arm. Two types of Y chromosome are present in inbred mouse strains: the Mus musculus musculus type and M.m. domesticus type. Among 26 inbred strains surveyed, 145SC5 detected polymorphims only in the M.m. domesticus Y chromosome.

Amino Acid Sequence↗
PubMed1990

Prenatal diagnosis of chromosome abnormalities. A comparison of the results of various techniques, with special emphasis on mosaicism.

Prenatal diagnosis of chromosome abnormalities can be performed on three different samples; chorion villi (CVS), amniotic fluid (AFS) and fetal blood (FBS). We are presenting data from our own experience on the chromosome analysis of 957 CVS, 1000 AFS and 927 FBS. A total of 69 chromosome abnormalities have been detected in the CVS, 38 in the AFS and 115 in the FBS. The type of abnormalities and their frequencies are compared between the three sampling methods. Our findings are in agreement with published data, and the higher incidence of chromosomal aberrations in the FBS group reflect the greater efficiency with which aneuploidies associated with more severe congenital malformation can be detected by ultrasound. Finally, we reported 18 cases of mosaicism in CVS, 76 in AFS and 31 in FBS. Of these cases, only 10 represented a true mosaicism of the fetus, 98 cases have been classified as pseudomosaicisms and 7 identified as maternal contamination. We have encountered 9 cases of mosaicism confined to the chorionic villi and 1 case limited to the amniotic fluid cells. There appeared to be a similarity between trisomies involved in chorion confined mosaicisms and pseudomosaicism cases of the AFS. The chromosome complement of the placenta may play an important role in the development of the pregnancy, and although a mosaic result in prenatal diagnosis could present difficulties in in the prediction of the fetal karyotype, it might give important information on the general condition of the fetus.

Amniocentesis↗
PubMed1989

The application of automated metaphase scanning to direct preparations of chorionic villi.

In order to increase the speed of analysis of metaphases from chorionic villi direct preparations, we have investigated the use of two automatic scanning devices, the Magiscan II and a version of Metafip (the research laboratory precursor of Cytoscan). The speed, efficiency, and ranking system have been compared to manual scanning. Results show that both machines detect approximately 80 per cent of the total analysable metaphases detected by a trained cytogeneticist. There appears to be reasonable agreement in ranking between methods.

Chorionic Villi↗
PubMed1989

Spontaneous and induced chromosome breakage in chorionic villus samples: a cytogenetic approach to first trimester prenatal diagnosis of ataxia telangiectasia syndrome.

Patients with ataxia telangiectasia (AT) syndrome exhibit a high level of spontaneous chromosome aberrations, with hypersensitivity to gamma radiation and radiomimetic chemicals at the chromosomal and cellular level. Previously pregnancies at risk for AT have been screened solely by analysis of amniotic fluid samples. In this report we describe a cytogenetic approach to the prenatal diagnosis of AT using chorionic villus sampling (CVS). Levels of spontaneous and induced (gamma radiation and bleomycin) chromosome breakage were established in direct, semidirect, and culture preparations of CVS samples from normal pregnancies. The methods developed were then successfully applied to the screening of a pregnancy at risk for AT. Semidirect preparations showed normal levels of chromosome breakage, and this result was further confirmed in chorion, amniotic fluid, and lymphocyte cultures. In chorion villus samples, gamma radiation is probably the easiest and most reliable way of discriminating between unaffected fetuses and those with AT.

Adult↗
PubMed1988

Chromosome banding in direct preparations of chorionic villi.

Chorionic villus sampling (CVS) is now currently offered for first trimester prenatal diagnosis of genetic disorders. Chromosome analysis of CVS in direct and culture preparations is possible using modifications of standard banding techniques. We summarize our experience in applying QFQ, GTG, RBG, CBG, DA/DAPI, NOR, and SC differentiation protocols to direct preparations. Characteristic chromosome regions are properly labelled by these techniques, and analysis of 300 band stage karyotypes is consistently achievable on GTG banded direct preparations. However, banding of CVS direct chromosomes has proved to be difficult, and the analysis needs to be backed up by culture preparations.

Chorionic Villi↗
PubMed1988

Cell cycle studies in chorionic villi.

We have studied the cell cycle of cells obtained from chorionic villi in direct and culture preparations by incorporation of the thymidine analogue BrdU to produce late-labelling or sister chromatid differentiation patterns. We have, therefore, been able to estimate the duration of the cell cycle and, more specifically, the length of some of its phases. While results for chorionic villus sample cells in culture resembled those obtained for fibroblasts, data for the spontaneously dividing trophoblastic cells in direct preparations were different. Villi exposed to BrdU immediately after sampling showed a slight delay in the incorporation of the analogue and a lower percentage of labelled cells compared to villi treated after an overnight incubation, probably due to a temporary effect of the sampling technique. Results from semi-direct protocols suggest that cells have a G2 of no more than 4 h, and a mid-S phase of 10-16 h. The G1 period is very variable. After 48 h incubation with BrdU, only 4% of cells reach their second generation, whereas this percentage increases up to 70% after 72 h, indicating that under these experimental conditions most cells have a cell cycle of approximately 36 h. The average number of sister chromatid exchanges was similar in both direct preparations and cultures: 5.2 +/- 2.1 SCE per cell.

Cell Cycle↗
PubMedDate not supplied

A familial case of recurrent hydatidiform molar pregnancies with biparental genomic contribution.

Hydatidiform mole is a benign trophoblastic neoplasia characterized by an abnormal development of the embryo and proliferation of placental villi. Using microsatellite markers amplified by the polymerase chain reaction, we have performed a genetic study on eight independent molar tissues occurring in two sisters. Karyotype and genotype data demonstrate a diploid and biparental constitution in seven of the analyzed moles suggesting a common mechanism underlying the etiology of the various molar pregnancies in this family. The data reported here suggest that complete and partial hydatidiform moles are not always separate entities and that women with familial recurrent hydatidiform moles are homozygous for an autosomal recessive mutation.

Diploidy↗
PubMedDate not supplied

The spectrum of beta-thalassaemia mutations in the Lebanon.

We screened 110 DNA samples from carriers of beta-thalassaemia, using the ARMS-PCR technique with primers for common Mediterranean mutations. Unidentified samples were subjected to a heteroduplex analysis with Universal Heteroduplex Generators covering the beta-globin gene, followed by DNA sequencing. In total, 16 different mutations were detected, the most frequent being IVSI-110 (40%), followed by other common Mediterranean mutations (IVSI-1, IVSII-1, IVSI-6). Other mutations detected were of Lebanese, Turkish, Iranian, Kurdish, Bulgarian and Asian Indian origin. The most heterogeneous religious group seems to be the Sunni Muslims, with 13 mutations, while only 2 mutations were detected among the Christian Maronites. Results from this study are compared with those from other Mediterranean and neighbouring countries.

Community Medicine↗
PubMedDate not supplied

[Retrospective study of nine Lebanese families with fragile X syndrome and review of the literature].

The Fragile X syndrome is the most common inherited form of mental retardation. Despite its incidence, which is estimated at 1/4000 boys, only 9 families have been documented so far in Lebanon, of which 3 have been partially investigated. This syndrome therefore seems to be largely ignored by physicians. Although no treatment is yet available for the Fragile X syndrome, the diagnosis of the disorder in a child is essential in order to provide the family with genetic counselling. The most critical point is still to convince the family of the need for such an evaluation and relieve the parents of any feeling of guilt.

Adult↗
PubMedDate not supplied

Karyotype of amniotic fluid cells at the AUB-MC results on 2000 cases.

We report results on 2000 cases of amniotic fluid referred for karyotype analysis. Referrals were advanced maternal age in 64% of cases and abnormal ultrasound in 12% of cases. The frequency of chromosome aneuploidy was 2.4% in the first category and that of chromosome abnormalities 8% in the second. The incidence of marker chromosomes was 0.25%, that of mosaicism 0.3%, and maternal cell contamination was observed in 0.6% of cases. The overall culture failure rate was 0.9%. Our results are mostly in accordance with figures from larger surveys, published in the literature and differences might be due to the smaller number of samples in this series and variation in referral and/or sampling protocols.

Academic Medical Centers↗
PubMedDate not supplied

Constitutional chromosome abnormalities among patients referred for blood karyotype analysis: a 5-year study at the AUBMC.

We report results on 2010 cases of blood referred for constitutional karyotype analysis. Referrals were grouped into 16 different categories, of which reproductive failure represented the highest percentage (33%), followed by structural congenital abnormalities (14.17%), developmental delay (11.34%), Down syndrome (9.65%), and abnormal sexual development (8.16%), while other categories represented smaller percentages. The total rate of abnormality was 16%, and the highest abnormality rates were among the clinically-recognizable chromosomal syndromes, while lower percentages were detected among less specific referrals. However, abnormality rates were generally different from the typical reported rates, probably due to the inclusion of cases not requiring chromosome analysis or the failure to recognize specific chromosomal syndromes. Other identified problems included lack of proper phenotypic description and difficulty in obtaining familial follow-up for proper diagnosis and genetic counseling.

Chromosome Aberrations↗
PubMedDate not supplied

Karyotype analysis in chronic myelogenous leukemia. A three-year experience at the American University of Beirut Medical Center (AUBMC).

We report the results of karyotype analysis on cases referred to our laboratory for chronic myelogenous leukemia (CML) over a period of three years. A total of 68 patient were referred and a karyotype was successfully obtained in all cases except one. Thirty-one percent of cases were found to have a normal karyotype, 58.5% were Philadelphia (Ph1) positive while 10.5% of cases had chromosome abnormalities other than Ph1. Among the Ph1 positive cases, 92% had the standard translocation (9;22), 7.7% had a variant translocation and 12.8% had additional chromosome abnormalities. Our results are compared to those generally reported in the literature and the comparisons are discussed.

Adult↗