1/18. angelman syndrome with uniparental disomy due to paternal meiosis II nondisjunction.We report a case of angelman syndrome (AS) with paternal uniparental disomy (pUPD) of chromosome 15. This 6-year-old girl with overgrowth had frequent, but only provoked laughter, was mildly ataxic with limb hypertonia, and had no intelligible speech. She had deep-set eyes, protruding tongue, and prominent chin. The karyotype was normal. dna analysis with microsatellites from chromosome 15 showed no inheritance of maternal alleles both within and outside the AS critical region. Proximal markers showed reduction to homozygosity of paternal alleles, intermediate markers showed nonreduction, and distal markers reduction, thus suggesting a meiosis II nondisjunction event in the father with two crossovers. This is, to our knowledge, the first reported case of AS due to meiosis II nondisjunction. We present detailed physical measurements in this patient, adding to the clinical description of the milder phenotype in AS due to pUPD.- - - - - - - - - - ranking = 1keywords = nondisjunction (Clic here for more details about this article) |
2/18. Premature chromosome condensation in humans associated with microcephaly and mental retardation: a novel autosomal recessive condition.We report a novel autosomal recessive disorder characterized by premature chromosome condensation in the early g2 phase. It was observed in two siblings, from consanguineous parents, affected with microcephaly, growth retardation, and severe mental retardation. Chromosome analysis showed a high frequency of prophase-like cells (>10%) in lymphocytes, fibroblasts, and lymphoblast cell lines with an otherwise normal karyotype. (3)H-thymidine-pulse labeling and autoradiography showed that, 2 h after the pulse, 28%-35% of the prophases were labeled, compared with 9%-11% in healthy control subjects, indicating that the phenomenon is due to premature chromosome condensation. flow cytometry studies demonstrate that the entire cell cycle is not prolonged, compared with that in healthy control subjects, and compartment sizes did not differ from those in healthy control subjects. No increased reaction of the cells to X-irradiation or treatments with the clastogens bleomycin and mitomycin C was observed, in contrast to results in the cell-cycle mutants ataxia telangiectasia and fanconi anemia. The rates of sister chromatid exchanges and the mitotic nondisjunction rates were inconspicuous. Premature entry of cells into mitosis suggests that a gene involved in cell-cycle regulation is mutated in these siblings.- - - - - - - - - - ranking = 0.16666666666667keywords = nondisjunction (Clic here for more details about this article) |
3/18. Concurrence of fragile X and Klinefelter syndromes: report of a new case of paternal nondisjunction.The concurrence of fragile X and Klinefelter syndromes would be expected occasionally. Therefore, the analysis of the literature showed that the concurrence of both conditions was found at least 16 times. Among them, only seven cases were analyzed for the parental origin of the extra chromosome X, suggesting that the maternal nondisjunction was preferentially inherited. We present the third patient with the concurrence of fragile X and Klinefelter syndromes, in which the parental origin of the supernumerary chromosome X was paternal. This finding reinforces that the parent-of-origin predisposition of the concurrence of the fragile X and Klinefelter syndromes is a pure coincidence.- - - - - - - - - - ranking = 0.83333333333333keywords = nondisjunction (Clic here for more details about this article) |
4/18. Monozygotic twins with discordant sex.A nine-year-old girl with short stature was referred to the department of pediatrics at Kyushu University. The clinical diagnosis was turner syndrome; karyotypic analysis performed on peripheral blood, using GTG techniques, demonstrated a 45,X/47,XYY (17:83) mosaicism. Her twin brother, a phenotypically normal male, had the same karyotype; 45,X/47,XYY (3:97) on peripheral blood. Their skin fibroblast karyotypes showed the same mosaicism, ie. 45,X/47,XYY (41:59 and 31:69 respectively). On eleven biochemical genetic markers the twin pair were concordant, thus the likelihood of monozygosity was 0.99527034. In addition, the analysis of variable number of tandem repeat (VNTR) markers revealed the likelihood of monozygosity to be 0.99944386. The most plausible explanation of the X/XYY mosaicism was nondisjunction of the Y in the first cleavage division of the 46,XY zygote. A disproportionate rate of cell populations with 45,X and 47,XYY in the twinning process of the X/XYY embryo, especially in the germ lines, would result in discordant sex in twin pairs.- - - - - - - - - - ranking = 0.16666666666667keywords = nondisjunction (Clic here for more details about this article) |
5/18. The unbalanced offspring of the male carriers of the 11q;22q translocation: nondisjunction at meiosis II in a balanced spermatocyte.Carriers of the standard translocation t(11;22) (q23.3;q11.2) produce only one type of unbalanced offspring, a tertiary trisomy resulting into the karyotype 47,XX or XY, der(22)t(11;22)(q23.3;q11.2), usually derived from the mother. The exception is one single patient 47,XY,t(11;22)(q23.3;q11.2), der(22)t(11;22) (q23.3;q11.2)pat. We report a second case with the same karyotype, also of paternal origin. Thus, the rare unbalanced offspring of a carrier father (only 5 cases known) may receive a supernumerary der(22), as a consequence of tertiary trisomy, but also as a consequence of nondisjunction at meiosis II of a balanced spermatocyte.- - - - - - - - - - ranking = 0.83333333333333keywords = nondisjunction (Clic here for more details about this article) |
6/18. Second meiotic nondisjunction of the rearranged chromosome in a familial reciprocal 5/13 translocation.We describe a 20-week-gestation male fetus with partial dup(5p) and proximal dup(13q), 47,XY,t(5;13)(p15;q21), der(13)t(5;13)(p15;q21) mat. This finding is attributable to second meiotic nondisjunction of the rearranged chromosome in a maternal balanced reciprocal translocation. To the best of our knowledge, there have been only 3 previous reports of a similar error in the segregation of the rearranged chromosomes. For the first time evidence has been given that this unusual segregation is due to maternal second meiotic nondisjunction, using QFQ banding heteromorphisms. Second meiotic malsegregation should be taken into account in the consideration of reproductive problems in carriers of balanced translocations.- - - - - - - - - - ranking = 1keywords = nondisjunction (Clic here for more details about this article) |
7/18. Determination of the origin of nondisjunction in a 49,XXXXY male using hypervariable dinucleotide repeat sequences.We present a patient with a 49,XXXXY chromosome constitution in whom the origin of the extra X chromosomes was determined by analysis of five polymorphic CA (or GT) dinucleotide repeat sequences. This class of dna marker has recently been demonstrated to be hypervariable with heterozygosity values up to 80%. By polymerase chain reaction (PCR) analysis of the dinucleotide repeat length polymorphisms, we have shown that all four X chromosomes were of maternal origin.- - - - - - - - - - ranking = 0.66666666666667keywords = nondisjunction (Clic here for more details about this article) |
8/18. Free proximal trisomy 21 in the mother and malformation syndrome in the son.We report on a new case of duplication of the proximal part of the long arm of chromosome 21. The proposita presents normal mental development, no trisomy 21 manifestations; on the contrary, she had a few monosomy 21-like stigmata. She gave birth to a severely malformed infant with a pattern of malformations suggesting a partial 21-monosomy syndrome, but with a 46,XY normal karyotype in his peripheral blood lymphocytes. The findings are explained in the following way: the infant probably had originally a 47,XY, 21q- karyotype like his mother. Post zygotic nondisjunctional events produced a prevalent 46,XY,21q- line responsible for the severe malformations and the normal 46,XY line found in his blood lymphocytes.- - - - - - - - - - ranking = 0.16666666666667keywords = nondisjunction (Clic here for more details about this article) |
9/18. Maternal meiosis II nondisjunction in a case of 47,XXY testicular feminization.An 11-year-old patient with incomplete testicular feminization and a 47,XXY karyotype is described. The patient had female external genitalia, clitoromegaly, and some features of Klinefelter's syndrome, including speech delay and delayed intellectual development. dna analysis using X chromosomal dna sequences suggest that the supernumerary x chromosome in the patient resulted from maternal nondisjunction during meiosis II. The M II error thereby provides the basis for homozygosity of a mutation in the androgen receptor locus.- - - - - - - - - - ranking = 0.83333333333333keywords = nondisjunction (Clic here for more details about this article) |
10/18. Nucleolar organizer region heteromorphism associated with trisomy-21: a risk factor for non-disjunction?An unusual nucleolar organizer region (double NOR) on chromosome 13 was observed in a down syndrome child [47, XY, 21, dNOR(13)]. The variant chromosome was inherited from the mother [46, XX, dNOR(13)]. The extra chromosome 21 in the proband was maternal origin. The frequency of NOR chromosome association showed relatively high frequency in the mother and proband as compared to the controls. The result suggest that chromosome variants involving extra copies of NOR may indeed be involved in the meiotic nondisjunction of chromosome-21.- - - - - - - - - - ranking = 0.16666666666667keywords = nondisjunction (Clic here for more details about this article) |
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