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PubMedDate not supplied

Mosaic unbalanced structural abnormalities confirmed using FISH on buccal mucosal cells.

Three rare mosaic unbalanced structural rearrangements found in routine peripheral blood analysis were confirmed in buccal mucosal cells using interphase FISH. Case 1 had a de novo mosaic triplication for 13q22q33 found in 22.5 % lymphocytes. D13S585 probe that maps to 13q32q33 confirmed the mosaicism in 41 % of buccal mucosal cells. Case 2 had additional material on a 3q derived from 14q31qter in 83 % of lymphocytes. The 14q-subtelomeric probe was used on buccal smear cells: 86 % had three signals and 14 % had two signals. Case 3 was a mosaic de novo add(5) in 32 % lymphocytes. The additional material was from 3p26pter. The 3p-subtelomere probe confirmed the mosaicism in 40 % buccal epithelial cells. This study shows the applicability of interphase FISH to confirm mosaic unbalanced rearrangements in a second tissue such as buccal mucosal cells.

Abnormalities, Multiple↗
PubMed2002

Trisomy 13 or 18 (mosaicism) in first trimester cytotrophoblast cells: false-positive results in 11 out of 51 cases.

OBJECTIVE: The finding of full or mosaic trisomy 13 or 18 in first trimester chorionic villus sampling (CVS) may be a false-positive result. This report provides incidence and outcome information that may be helpful in counselling individual patients and in choosing adequate follow-up. STUDY DESIGN: From a series of 6820 CVS cases, we retrospectively collected data on all patients (n=51) with full (n=30) or mosaic (n=5) trisomy 18, and full (n=13) or mosaic (n=3) trisomy 13 in cytotrophoblast cells. RESULTS: Five false-positives were seen in patients with full trisomy 18 and three in the mosaic cases. One false-positive result was observed in full trisomy 13 and two false-positives in cases of mosaicism. No false-negative results were reported. CONCLUSION: The diagnosis of trisomy 13 or 18 in cytotrophoblasts should be confirmed in other tissues, unless fetal abnormalities are seen at ultrasound. In case of mosaicism, follow-up amniocentesis is advised.

Amniocentesis↗
PubMed2002

The role of tangential dispersion in retinal mosaic formation.

Individual types of retinal nerve cell are spaced across the retina in an orderly manner, ensuring a uniform sampling of the visual field. This regularity in cellular spacing has been commonly attributed to fate determination mechanisms operating around the time of cell birth, an hypothesis presuming that the position of a nerve cell is fixed within the plane of the retina from the time of its determination. At odds with this view, recent results from X-inactivation mosaic mice indicate that certain classes of retinal nerve cell, those known to form orderly mosaics in the adult retina, disperse tangentially during development. Furthermore, studies defining the spatial characteristics of developing and mature retinal mosaics suggest that cell-cell interactions around the time of morphological differentiation lead to mutual repulsion. Modelling studies in turn show that nothing more than a simple minimal spacing rule between neighboring cells of the same type is sufficient for the creation of the global patterning observed in biological retinal mosaics. For some cell types, the size of this "exclusion zone" surrounding individual cells is shown to be an intrinsic characteristic of each cell type, invariant across the retina, and accounting for the variation in mosaic regularity across changes in cell density. These results show how short-distance movements driven by intercellular interactions at the local level may mediate the emergence of the global patterning characteristic of retinal mosaics during development.

Animals↗
PubMed1999

High frequency of tissue-specific mosaicism in Turner syndrome patients.

Interphase fluorescent studies of X chromosome aneuploidy in cultured and uncultured blood lymphocytes and oral mucosa epithelial cells using X centromere-specific DNA probe in addition to standard karyotype analysis were performed in 50 females with a clinical suspicion of Turner syndrome. All the patients were previously screened for the presence of 'hidden' Y chromosome mosaicism, using the primers DYZ3 and DYZ. The use of fluorescence in situ hybridization (FISH) analysis of interphase nuclei of tissues from different germ layers (lymphocytes from mesoderm and buccal epithelial cells from ectoderm) improves the accuracy of detection of low-level mosaicism. FISH studies on interphase nuclei revealed that 29% of patients with a pure form of monosomy X detected by metaphase analysis are, in fact, mosaics. The level of cells with the normal chromosomal constitution in lymphocytes of these cases as a rule was low, ranging from 3 to 18%, with an average of 7%. Two false-positive cases and one false-negative case of X monosomy mosaicism determined by standard cytogenetic approach were detected using FISH analysis. The majority of patients (92%) with mosaic form of Turner syndrome have considerable tissue-specific differences in levels of X aneuploidy. Our data indicate that in cases when mosaic aneuploidy with low-level frequency is questionable (approximately 10% and lower), the results of standard metaphase analysis should be supplemented with additional FISH studies of interphase nuclei. Tissue-specific differences in contents of different cell lines in the same patients point to the necessity of studying more than one tissue from each patient.

Adolescent↗
PubMed2004

Inverted duplications: how many of them are mosaic?

The best-known situation indissolubly linked to mosaicism is the uniparental disomy where a trisomic or monosomic zygote develops at least one cell line with 46 chromosomes. The mosaicism normal/abnormal cell lines may remain confined to placenta or persist in the embryo. Here, we describe a second situation that might also be indissolubly linked to a mosaic condition or at least to a confined placental mosaicism. We analysed the case of a mosaicism del(8p)/inv dup(8p) found in prenatal diagnosis. We had already demonstrated that the first product of the abnormal meiotic recombination at the basis of the inv dup rearrangements is a dicentric chromosome. Its breakage leads to the formation of a deleted and an inv dup chromosome. Although we had previously assumed that the dicentric underwent a breakage at meiosis II so that the zygote inherited the inv dup chromosome, our findings and those of others indeed indicate that the dicentric may be inherited in the zygote and that it might persist as such in early postzygotic stages, then undergoing different breakages in different cells leading to different abnormal chromosomes, either deleted or duplicated. Selection versus the most viable cell line(s) results either in a confined placental mosaicism with the inv dup cell line as the only one present in the embryo or in children with both the deleted and the inv dup cell lines. Phenotype/karyotype relationships in inv dup rearrangements must also take into account the influence of the other abnormal cell line during embryogenesis.

Aborted Fetus↗
PubMed2005

Trisomy 7 mosaicism, maternal uniparental heterodisomy 7 and Hirschsprung's disease in a child with Silver-Russell syndrome.

Prenatal trisomy 7 is usually a cell culture artifact in amniocytes with normal diploid karyotype at birth and normal fetal outcome. In the same way, true prenatal trisomy 7 mosaicism usually results in a normal child except when trisomic cells persist after birth or when trisomy rescue leads to maternal uniparental disomy, which is responsible for 5.5-7% of patients with Silver-Russell syndrome (SRS). We report here on the unusual association of SRS and Hirschsprung's disease (HSCR) in a patient with maternal uniparental heterodisomy 7 and trisomy 7 mosaicism in intestine and skin fibroblasts. HSCR may be fortuitous given its frequency, multifactorial inheritance and genetic heterogeneity. However, the presence of the trisomy 7 mosaicism in intestine as well as in skin fibroblasts suggests that SRS and HSCR might possibly be related. Such an association might result from either an increased dosage of a nonimprinted gene due to trisomy 7 mosaicism in skin fibroblasts (leading to SRS) and in intestine (leading to HSCR), or from an overexpression, through genomic imprinting, of maternally expressed imprinted allele(s) in skin fibroblasts and intestine or from a combination of trisomy 7 mosaicism and genomic imprinting. This report suggests that the SRS phenotype observed in maternal uniparental disomy 7 (mUPD(7)) patients might also result from an undetected low level of trisomy 7 mosaicism. In order to validate this hypothesis, we propose to perform a conventional and molecular cytogenetic analysis in different tissues every time mUPD7 is displayed.

Adult↗
PubMed2000

Confined placental mosaicism and genomic imprinting.

The concept of confined placental mosaicism and its relationship to genomic imprinting and uniparental disomy is explained in this chapter. Clinically significant imprinting syndromes, such as Prader-Willi syndrome, Angelman syndrome, Beckwith-Wiedemann syndrome, Silver-Russell syndrome and transient neonatal diabetes mellitus, potentially associated with confined placental mosaicism are described and referenced. Non-Mendelian inheritance of recessive mutations in uniparental disomy is illustrated. Both skewed X chromosome inactivation and isolated gonadal mosaicism are outlined as newly recognized consequences of post-zygotic chromosomal mutation and confined placental mosaicism. Clinical management of pregnancies with confined placental mosaicism is proposed as well as future research directions in the field of confined placental mosaicism and its consequences.

Abnormalities, Multiple↗
PubMed1996

Spontaneous mutations recovered as mosaics in the mouse specific-locus test.

The specific-locus test (SLT) detects new mutants among mice heterozygous for seven recessive visible markers. Spontaneous mutations can be manifested not only as singleton whole-body mutants in controls (for which we report new data), but as mosaics-either visible (manifesting mottled coat color) in the scored generation (G2) or masked, among the wild-type parental generation (G1). Masked G1 mosaics reveal themselves by producing clusters of whole-body mutants in G2. We provide evidence that most, if not all, mosaics detected in the SLT (both radiation and control progenies) result from a single-strand spontaneous mutation subsequent to the last premeiotic mitosis and before the first postmeiotic one of a parental genome-the "perigametic interval." Such events in the genomes of the G1 and Gzero results, respectively, in visible and masked 50:50 mosaics. Per cell cycle, the spontaneous mutation rate in the perigametic interval is much higher than that in pregamete mitotic divisions. A clearly different locus spectrum further supports the hypothesis of different origin, and casts further doubt on the validity of the doubling-dose risk-estimation method. Because mosaics cannot have arisen in mitotic germ cells, and are not induced by radiation exposure in the perigametic interval, they should not be included in calculations of radiation-induced germ-line mutation rates. For per-generation calculations, inclusion of mosaics yields a spontaneous frequency 1.7 times that calculated from singletons alone for mutations contributed by males; including both sexes, the multiple is 2.2.

Animals↗
PubMed1995

Somatic mosaicism in sperm is associated with intergenerational (CAG)n changes in Huntington disease.

We have analysed the CAG repeat in the Huntington disease (HD) gene in sperm and blood from 20 unrelated HD patients. Although the CAG repeat displayed significant mosaicism in sperm from all individuals, there were marked differences in the degree of repeat instability. Individuals who had either inherited or transmitted an expanded CAG repeat displayed the highest levels of repeat mosaicism, whereas individuals who had inherited or transmitted a contracted repeat had very limited CAG mosaicism in sperm. A strong association between intergenerational change in CAG allele size and the level of sperm repeat mosaicism was determined (P = 0.019). In contrast, neither blood CAG size nor repeat mosaicism in blood, were significantly associated with intergenerational CAG changes. These data suggest the presence of a cis-acting factor, separate from CAG size, that strongly influences the intergenerational behaviour of the CAG repeat. Additional studies are needed to determine whether analysis of CAG mosaicism in sperm is useful for assessing an individual's risk for transmitting large expansions or contractions to his offspring.

Adolescent↗
PubMed2004

Detailed FISH analysis of day 5 human embryos reveals the mechanisms leading to mosaic aneuploidy.

BACKGROUND: Fluorescence in situ hybridization (FISH) analysis has shown that human embryos display a high level of chromosomal mosaicism at all preimplantation stages. The aim of this study was to investigate the mechanisms involved by the use of two probes for each of three autosomes at different loci and to determine the true level of aneuploid mosaicism by excluding FISH artefacts. METHODS: Embryos were cultured in two different types of medium: group I were cultured in standard cleavage medium for up to day 5 and group II were cultured from day 3 to day 5 in blastocyst medium. Three rounds of FISH were performed. In round 1, the probes used were 1pTel, 11qTel and 18CEP; in round 2, the probes used were 1satII/III, 11CEP and 18qTel; in round 3, the probes used were 18CEP, XCEP and YCEP. RESULTS: A total of 21 embryos were analysed in each group. The FISH results revealed one uniformly diploid and 20 mosaic embryos for group I, and two uniformly diploid and 19 mosaic embryos for group II. The predominant type of mosaicism was diploid/aneuploid. The use of two different probes per autosome was able to distinguish FISH artefacts affecting 5% of nuclei from true single cell anomalies. CONCLUSIONS: Post-zygotic chromosome loss was the most common mechanism leading to aneuploidy mosaicism for both groups, followed by chromosome gain, with fewer examples of mitotic non-disjunction.

Adult↗
PubMedDate not supplied

Broad resistance to tobamoviruses is mediated by a modified tobacco mosaic virus replicase transgene.

Tobacco plants made transgenic to express the wild type tobacco mosaic virus (TMV) 183-kDa replicase gene were not resistant to TMV. However, transgenic plants containing essentially the same sequences, but with an additional insertion that would terminate translation in the middle of the 183-kDa gene, were highly resistant to systemic infection by TMV and other tobamoviruses. The 1.4-kbp insertion in the replicase open reading frame (ORF) of the resistant plants was shown by DNA sequencing to be an IS10-like transposable element, which apparently inserted itself into the TMV sequence at nucleotide 2875 sometime during the propagation of this replicase ORF plasmid (pREP21). Because of four stop codons, in frame with the TMV replicase ORF on the immediate 5' border of the IS insertion, REP21 effectively represents domain 1 (putative methylase domain) and a portion of domain 2 (putative helicase domain) of the TMV replicase ORF. REP21 Xanthi tobacco plants had a level of resistance to TMV similar to other reported transgenic replicase plants. No TMV was detected in upper leaves of these plants at 1-mo postinoculation. In addition, REP21 plants were resistant to an unusually broad range of tobamoviruses including tomato mosaic virus, tobacco mild green mosaic virus, TMV-U5, green tomato atypical mosaic virus, and ribgrass mosaic virus. These plants were not resistant to cucumber mosaic cucumovirus. The lack of systemic infection by TMV was due to reduced multiplication in inoculated leaves rather than complete prevention of replication.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1994

Chromosome mosaicism in human embryos.

In the human, mosaicism may occur before implantation; but, to determine when it first occurs, it is necessary to study the chromosomal complement of all blastomeres. Full karyotypes of blastomeres from 2- to 8-cell human embryos by conventional karyotyping of metaphase spreads are difficult to obtain. The aim of this study was to assess the stage at which mosaicism occurred in preimplantation human embryos through use of fluorescence in situ hybridization (FISH) with multiple probes. All or most blastomeres from 2- to 12-cell human embryos were analyzed by FISH using probes for gonosomes and chromosome 18. FISH was performed on blastomeres from 117 morphologically normal monospermic embryos that were not transferred after preimplantation diagnosis because of their risk of carrying X-linked disease; 20 (17.1%) of these embryos were mosaic. Another group of 163 arrested or morphologically abnormal monospermic embryos were also analyzed by FISH; 47 (28.8%) of these embryos were mosaic. In addition, 37 dispermic embryos were analyzed, and 28 (75.7%) of these were found to be mosaic. Mosaicism first occurred at the second cleavage division when the monospermic embryo was mostly diploid and at the first cleavage division when the embryo was mostly haploid, polyploid, or dispermic.

Blastomeres↗
PubMed2000

Modeling of mosaic patterns in chimeric liver and adrenal cortex: algorithmic organogenesis?

If organogenesis were a completely deterministic process, then the amount of information required to store the spatial position and fate of every cell in vertebrate organisms would be larger than the total information that could be contained in their genomes. This suggests that the instructions of developmental mechanisms involved in organogenesis, coded in DNA, must be at least in part procedural or algorithmically based. Chimeric mosaic patterns in rat livers have been shown to be isotropic and to have fractal profiles (D approximately 1.3) whereas adrenal gland mosaics show a less irregular radial pattern, with lower fractal dimension (D approximately 1.2) than in the liver. These findings suggested a possible model of parenchyma generation. We propose that during organogenesis in both liver and adrenal cortex, the same basic mechanism is directed to organ mass enlargement, whereas the differences observed in mosaic patterns between the organs could be due to the control of a single parameter, namely, a form of contact inhibition. Computer simulations in two dimensions returned comparable results in both the fractal dimension value of mosaic patches and appearance of the mosaic 'tissues', as observed histologically in chimeras. This suggests that position information and locomotion of cells would not be required to produce the mosaic pattern observed in chimeras.

Adrenal Cortex↗
PubMed2002

Prenatal diagnosis of mosaic trisomy 20 in New Zealand.

OBJECTIVE: Mosaic trisomy 20 is not an uncommon finding on amniocentesis or CVS. Unlike other mosaic aneuploidies it is a relatively benign abnormality which, along with a lack of long-term follow-up of cases, has led to uncertainty when counselling parents. We aimed to identify known mosaic trisomy 20 pregnancies in New Zealand in the last 10 years and document their outcome. DESIGN: Retrospective database review with prospective clinical follow-up. METHODS: Cases were identified from the databases of the two clinical genetic services, as well as the four regional cytogenetics laboratories. Medical records were reviewed and where patients were available they were offered follow-up. RESULTS: Fourteen cases were identified (13 on amniocentesis, one on CVS), all with low levels of mosaicism (8-50%). In 12 cases, the children were physically and developmentally normal, with the longest follow-up being 10 years. Minor anomalies were noted in two cases. There were no major malformations noted in any of the cases and where repeat karyotypes were performed on blood or urine cytology these were normal. CONCLUSIONS: This series confirms a much lower incidence of phenotypic abnormalities associated with mosaic trisomy 20 compared to other forms of mosaic aneuploidy. Attempts to predict which of these pregnancies will have poor outcomes have not proven to be reliable. We recommend that, if a detailed anatomy scan is normal, parents be counselled that the risk of abnormality is less than 10%. Further tests should be performed only on the basis of a clinical indication.

Adult↗
PubMedDate not supplied

Postnatal confirmation of prenatally diagnosed trisomy 20 mosaicism in a patient with linear and whorled nevoid hypermelanosis.

Linear and whorled nevoid hypermelanosis (LWNH) is characterized by hyperpigmented reticulate macules in a Blaschko linear arrangement without atrophy or preceding inflammation. Underlying chromosomal mosaicism was often assumed, but has been verified in only a few published cases. We report a 7-year-old boy with LWNH associated with congenital ventricular septal defect and psychomotor retardation. Prenatal chromosomal analysis of amniocytes revealed trisomy 20 mosaicism, which was not confirmed in peripheral blood lymphocytes after birth. Histologic sections of skin biopsy specimens taken at age 6 years showed hyperpigmentation of the basal epidermal layer with prominent melanocytes and isolated melanophages in the upper dermis. Cytogenetic analysis of cultured skin fibroblasts revealed an extra chromosome 20 in 5 of the 30 metaphases studied (17%). Mosaic trisomy 20 is one of the most common autosomal mosaicisms identified in amniocytes and is, as a rule, compatible with normal pregnancy outcome. In postnatal analysis of peripheral blood lymphocytes, an extra chromosome 20 could never be detected. However, when confirmed in skin fibroblasts, trisomy 20 mosaicism may be associated with systemic anomalies. The present case shows for the first time an association of LWNH with trisomy 20 mosaicism and emphasizes the importance of analyzing skin fibroblasts in cases of prenatally diagnosed trisomy 20.

Abnormalities, Multiple↗
PubMed1979

Dermatoglyphic distances and position of 21 trisomy mosaics.

The position of 21 trisomy mosaics with an average proportion of trisomic cells approximating 0.5 in relation to normal subjects and those with complete 21 trisomy has been evaluated by means of dermatoglyphic distances, using samples of 142 mosaics, 302 normal controls and 225 complete 21 trisomics for males and females separately and combined. Distances were calculated by means of the simplified D2k method. Penrose's "size and shape" analysis of variance has been applied for comparison to obtain distance coefficients, C2H, based on pattern intensities. Results indicate that mosaics are not intermediate but much closer to 21 trisomics in spite of the fact that the average proportion of trisomic cells in blood approximates 0.5; secondly, that the degree of deviation from the intermediate position of the mosaic sample is roughly proportional to the degree of cytological mosaicism. The position of mosaics is appreciably more intermediate in respect of finger-tip patterns than in respect of palmar and sole loops and triradii. The results obtained here have thus given evidence for the usefulness of dermatoglyphic distances, which enable all the differences in frequencies or means of the respective characters to be conveniently represented by a single number, in studies of the abnormal development of phenotypic characteristics in cases of incomplete trisomy.

Dermatoglyphics↗
PubMedDate not supplied

Chromosomal mosaicism in amniotic fluid cell cultures.

Six cases of chromosomal mosaicism detected in amniotic fluid cultures are described. In five of these there was no evidence of fetal mosaicism. In one case fetal mosaicism was demonstrated but only by the study of fibroblasts since blood cultures showed only normal cells. The implications of amniotic fluid mosaicism are discussed and it is concluded that this usually does not indicate fetal mosaicism. The value of repeated amniocentesis in the diagnosis of fetal mosaicism was demonstrated by findings in three of the cases. It is recommended that amniotic fluid cultures be harvested in situ for chromosome studies and that cytogenetic results be expressed as number of colonies karyotyped rather than as number of cells analyzed.

Adult↗
PubMed1978

Mosaicism and the trisomy 8 syndrome.

Three new cases of trisomy 8 mosaicism are presented; two have features corresponding with those usually found in this syndrome, whereas one is highly atypical. In view of the almost universal mosaicism of these patients, the literature is reviewed with an emphasis on the patterns of mosaicism found. There is little correlation between degree of mosaicism and extent of clinical abnormality. The degree of mosaicism differs in different tissues, fibroblasts being more informative of aneuploidy than lymphocytes, and there is some evidence that the degree of mosaicism varies with time. The reasons for these findings are discussed, with particular reference to the raised paternal age found in a proportion of the reported cases.

Abnormalities, Multiple↗