A non-isotopic in situ hybridisation study of the chromosomal origin of 15 supernumerary marker chromosomes in man

Fifteen patients presenting with mosaic or non-mosaic karyotypes containing a distamycin-DAPI negative de novo or familial supernumerary marker chromosome were studied with non-isotopic in situ hybridisation using a library of alphoid centromere specific and satellite II/III probes. The in situ hybridisation studies showed that seven markers were derived from satellited autosomes (three chromosome 13/21, two chromosome 14, two chromosome 22), six from non-satellited autosomes (two chromosome 4, one chromosome 12, one chromosome 16, two chromosome 19), and one from the Y chromosome. One non-mosaic marker was negative for all the alphoid and satellite II/III probes used.

Two families with Xq27.3 fragility, no detectable insert in the FMR-1 gene, mild mental impairment, and absence of the Martin-Bell phenotype

In 2 families, propositi were investigated because of mild developmental delay and, in one case, behavior disorders. Seven males in the 2 families were found to have a fragile site at Xq27.3 but the usual insert in the FMR-1 gene was absent. The affected males had mild, or in some cases, no clear intellectual impairment and did not have the Martin-Bell phenotype. Carrier females in one family tended to show a high level of cytogenetic expression of the fragile site but were clinically normal. It is not yet clear whether these families have unusual mutations in the FMR-1 gene or whether their fragile sites are different, but cytogenetically indistinguishable from, that associated with inserts in the FMR-1 gene.

Metabolic and immune effects of enteral ascorbic acid after burn trauma

A burned guinea-pig model (30 per cent BSA) was used to study the effect of vitamin C on immune and metabolic responses following burn trauma. Thirty-six guinea-pigs received identical enteral diets (175 kcal/kg) except for the amount of vitamin C. Groups I, II, III and IV were given formulae delivering no vitamin C, (1 RDA) 15 mg/kg/day, 75 mg/kg/day or 375 mg/kg/day, respectively. Resistance to infection was evaluated by injecting each animal with 0.1 ml of 1 x 10(9) Staph. aureus 502A subcutaneously on day 10. On day 14, Staph. aureus abscesses were excised and the numbers of viable colonies were determined. Results showed no statistical differences between groups in the clearance of Staph. aureus. From days 2 to 12, animals in groups I, II and III had body weights of approximately 97 per cent of preburn body weight. Animals in group IV, however, had a body weight gain, 102 per cent of preburn body weight on day 12. Animals in group IV also had significantly lower metabolic rates on day 12 as compared to the animals in the other groups. These results suggest that large amounts of vitamin C have beneficial effects on the maintenance of body weight and metabolic rate following burn trauma.

Characterization and molecular analysis of nondisjunction in 18 cases of trisomy 21 and leukemia

We recently began a cytogenetic and molecular study of nondisjunction in leukemic Down syndrome individuals to determine whether the mechanism by which the extra chromosome 21 originates predisposes the individual to leukemia. In the present report, we summarize our observations on 18 patients with trisomy 21 and acute or transient leukemia, including 11 patients with acute lymphocytic leukemia, three with acute myeloid leukemia, one with B-cell lymphoma, one with acute megakaryoblastic leukemia, and two with transient leukemia. Results of DNA marker studies of the parental origin of the extra chromosome 21 indicated that 16 of the 18 cases (89%) were maternally derived, a percentage similar to that seen among nonleukemic Down syndrome patients. We noted that most leukemic Down syndrome patients had one locus or more in which parental heterozygosity was maintained in the trisomic individual, indicating a meiotic rather than a mitotic origin for the trisomy.

Estimates of the frequency of chromosome abnormalities detectable in unselected newborns using moderate levels of banding

Data on structural chromosome abnormalities identified during prenatal diagnosis were used to estimate the number of such abnormalities that would be detectable in an unselected series of newborns using moderate levels of banding (400 to 500 bands). These estimates were compared with the rates detected in nonbanded surveys of newborns. Between 1976 and 1990 prenatal diagnosis using banding techniques was carried out in our laboratory on 14,677 women aged 35 and over. Among these, we detected 112 structural rearrangements, 32 unbalanced and 80 balanced. These figures were adjusted by two methods to give an estimate of the frequency of structural abnormalities in the newborn. Our data suggest that the use of moderate levels of banding increases the frequency of unbalanced structural abnormalities from 0.052 to 0.061% and of balanced structural abnormalities from 0.212 to 0.522%. Thus, the total number of chromosome abnormalities detectable in the newborn is increased from 0.60% in unbanded preparations to 0.92% in banded preparations.

Trisomy 21: association between reduced recombination and nondisjunction

To assess the association between recombination and nondisjunction of chromosome 21, we analyzed cytogenetic and DNA markers in 104 trisomy 21 individuals and their parents. Our DNA marker studies of parental origin were informative in 100 cases, with the overwhelming majority (94) being maternal in origin. This value is significantly higher than the 75%-80% maternal nondisjunction rate typically observed in cytogenetic studies of trisomy 21 and illustrates the increased accuracy of the molecular approach. Using the maternally derived cases and probing at 19 polymorphic sites on chromosome 21, we created a genetic map that spans most of the long arm of chromosome 21. The map was significantly shorter than the normal female linkage map, indicating that absence of pairing and/or recombination contributes to nondisjunction in a substantial proportion of cases of trisomy 21.

XY chromosome nondisjunction in man is associated with diminished recombination in the pseudoautosomal region

To assess the possible association between aberrant recombination and XY chromosome nondisjunction, we compared pseudoautosomal region recombination rates in male meiosis resulting in 47,XXY offspring with those resulting in 46,XY and 46,XX offspring. Forty-one paternally derived 47,XXYs and their parents were tested at six polymorphic loci spanning the pseudoautosomal region. We were able to detect crossing-over in only six of 39 cases informative for the telomeric DXYS14/DXYS20 locus. Subsequently, we used the data to generate a genetic linkage map of the pseudoautosomal region and found it to be significantly shorter than the normal male map of the region. From these analyses we conclude that most paternally derived 47,XXYs result from meiosis in which the X and Y chromosomes did not recombine.

Physical mapping across the fragile X: hypermethylation and clinical expression of the fragile X syndrome

The most common genetic cause of mental retardation after Down's syndrome, the fragile X syndrome, is associated with the occurrence of a fragile site at Xq27.3. This X-linked disease is intriguing because transmission can occur through phenotypically normal males. Theories to explain this unusual phenomenon include genomic rearrangements and methylation changes associated with a local block of reactivation of the X chromosome. Using microdissected markers close to the fragile site, we have been able to test these hypotheses. We present evidence for the association of methylation with the expression of the disease. However, there is no simple relationship between the degree of methylation and either the level of expression of the fragile site or the severity of the clinical phenotype.

Fragile Xq27.3 in female heterozygotes for the Martin-Bell syndrome

X inactivation studies have been carried out on lymphocytes from eight unrelated females heterozygous for the Martin-Bell syndrome. Four of these carriers were of normal IQ and four were mentally handicapped. When BrdU was used to differentiate between the active and inactive X chromosome an average of 55% of fra(X) were active in the retarded subjects, but only 27% were active in those of normal IQ. When 3H thymidine was used to differentiate between the active and inactive X chromosome, an average of 58% of mitoses from handicapped subjects and 33% of mitoses from normal subjects showed an active fra(X) in informative cells. These results are compared with previously published studies and it is concluded that the number of inactive fra(X) chromosomes calculated as a proportion of all cells scored is the same in mentally normal and mentally retarded subjects. However, the number of active fra(X) chromosomes is consistently higher in the retarded than in the normal females.

The parental origin of de novo X-autosome translocations in females with Duchenne muscular dystrophy revealed by M27 beta methylation analysis

The parental origin of 3 de novo X-autosome translocations in females with Duchenne Muscular Dystrophy (DMD) was studied by means of methylation analysis using the X-linked probe M27 beta. In all three the translocation was found to be paternal in origin. The parental origin of X-autosome translocations in females with and without DMD is compared with other structural abnormalities of the X and with autosomal translocations.

A cytogenetic and molecular reappraisal of a series of patients with Turner's syndrome

The results of a cytogenetic and molecular reinvestigation of a series of 52 patients with Turner's syndrome are reported. No evidence of Y chromosome material was found among the patients with a 45,X constitution but two patients were found to have a cell line with a r(Y) chromosome which was previously thought to be a r(X). The parental origin of the single X in the 45,X patients was maternal in 69% and paternal in 31%, a similar ratio to that seen among spontaneously aborted 45,X conceptuses. This suggests that X-chromosome imprinting is not responsible for the two grossly different phenotypes associated with a 45,X chromosome constitution. Approximately half of the structurally abnormal X chromosomes were maternal in origin and half paternal. This observation is consistent with either a meiotic or post-zygotic mitotic origin and at variance with the predominantly paternal origin reported for autosome structural abnormalities.

The parental origin of the extra X chromosome in 47,XXX females

We used X-linked DNA polymorphisms to study the parental origin of X chromosome nondisjunction in 28 47,XXX live-born females. Errors in oogenesis accounted for 26 of the cases, with the majority of these being attributable to an error at meiosis I. We observed an association between advanced parental age and meiosis I nondisjunction--but not meiosis II nondisjunction--in the maternally derived cases. In studies of recombination we found little evidence for an association between pairing failure and X chromosome nondisjunction, but our results suggest that increased recombination near the centromere may play a role in the etiology of the 47,XXX condition.

The role of chromosome abnormalities in reproductive failure

The frequency of chromosome abnormalities in spontaneous abortions, stillbirths, livebirths and among all clinically recognized pregnancies is given. Data on the parental origin of sex chromosome abnormalities and certain autosomal trisomies determined using molecular probes are presented and the proportion of sperm and eggs that are nullisomic or disomic for a sex chromosome to an autosome 16, 18 or 21 is calculated.

A centromere map of the X chromosome from trisomies of maternal origin

A centromere map is derived from XXX and XXY trisomies of maternal origin. Preliminary data suggest reduced recombination in the tetrads giving rise to mei I nondisjunction, but an excess of recombination in the pericentric region. As in Drosophila, multichiasmate tetrads may be more at risk of nondisjunction than nullochiasmate tetrads.

Studies of X-chromosome inactivation in trisomies

Previous studies of human triploidy have implicated the autosomes in the regulation of activity of X-linked genes. To determine if the influence of the extra autosomal set in triploids was attributable to a specific autosomal gene, we examined the pattern of DNA replication in females trisomic for 18 of the possible 22 autosomal trisomies. We find no evidence that a single gene or chromosome in triplicate can effect X-chromosome replication or activity. Our results suggest either that more than one locus in triplicate is required to maintain the activity of two X chromosomes, or that the influence of the extra autosomal set in enabling the activity of more than a single X chromosome is mediated indirectly, perhaps through the agency of increased nuclear size or changes in the cell cycle.

A cytogenetic study of 47,XXY males of known origin and their parents

A number of patients with both sex chromosome aneuploidy and the fragile X syndrome have been reported and this has led to the hypothesis that females heterozygous for the fragile X mutation have an increased rate of meiotic nondisjunction. Furthermore the suggestion has frequently been made that a predisposition to meiotic nondisjunction is associated with an increase in mitotic nondisjunction. We have tested these two hypotheses by examining the chromosomes of a series of 47,XXY males and their parents. In the majority the parental origin of the additional sex chromosome was known. The cells were cultured under conditions suitable for demonstrating the fragile X and 100 cells were scored 'blind' from the patients and both parents. No fragile X individual was seen and there was no difference in the proportion of aneuploid cells between the parents in whom the nondisjunction event occurred and the control parents. Therefore, our results lend no support to the suggestions that the fragile X is associated with an increase in sex chromosome aneuploidy or that individuals in whom meiotic nondisjunction occurs have an increased level of mitotic nondisjunction.

Maternal age in trisomy

By comparison with a more general theory, data on trisomy in live births, amniocenteses, and spontaneous abortions by year of maternal age are shown to fit a logistic augmented by a proportion independent of maternal age. The frequency of trisomy increases monotonically, with no discrepancy at extremely low or high maternal age. Trisomy 16 is exceptional in that all cases appear to be age-dependent. For groups A, B, and C most trisomies arise by a process independent of maternal age. A small proportion of these trisomies and about half of trisomies for smaller chromosomes (excluding trisomies 16 and perhaps 22) originate by some process dependent on maternal (but not paternal) age and therefore presumably independent of crossingover, which in the female takes place before birth.

Origin of sex chromosome aneuploidy

Probabilities applicable to RFLPs are derived for the genotypes of XXY, XXX, and XO children, conditional on their mode of origin and the parental mating type, and the theory is applied to family data on the XG locus. The proportion of XXY males arising in spermatogenesis is shown to be 0.41 +/- 0.09. The large distance of XG from the centromere makes distinction between maternal meiosis I and II unreliable, but if man is like Drosophila, most of the maternal non-disjunctions arise in meiosis I, among tetrads that have undergone one or more exchanges. Data from XG show that 0.78 +/- 0.05 of XO females arise from an error involving the paternal sex chromosomes. The XG locus is virtually uninformative about the origin of XXX. Application of the theory to selected RFLPs will be much more incisive because of their large number, lack of dominance, greater heterozygosity, and distribution along the chromosome. Study of RFLPs will facilitate diagnosis of the parental origin of sex chromosome abnormalities and the comparison of recombination rates in regular and trisomic progeny of maternal mei I and mei II origin. A pseudocentromeric model that estimates map distances from exceptional progeny is applied to non-disjunction of the X chromosomes in D. melanogaster, giving good recovery of the expected map and thereby validating this approach for RFLPs in man.

Klinefelter's syndrome: an analysis of the origin of the additional sex chromosome using molecular probes

The results of our study of the origin of the additional X chromosome in 39 males with a 47,XXY chromosome constitution are reported. We used a total of 20 X-linked RFLPs and successfully determined the origin of all 32 patients in whom DNA from both parents was available, and a further 3 in whom DNA was available from the patient and mother only. Males whose additional X chromosome was maternal in origin were further investigated using an X-linked centromere specific probe to determine the cell division at which the error occurred. Our results showed 53% of the non-disjunction to be attributable to pat mei I errors, 34% to mat mei I errors, 9% to mat mei II errors and 3% to a post-zygotic mitotic error. In the great majority of patients resulting from an error of maternal meiosis there was clear evidence of recombination involving the non-disjoined chromosomes, suggesting that absence of recombination is not an important aetiological factor in non-disjunction of the X chromosome in female meiosis. There was no alteration of parental age associated with the paternally derived 47,XXY males but a marked increase in maternal age among the maternally derived 47,XXY males, the increase being associated with mat mei I but not mat mei II errors. The proportion of paternally and maternally derived cases was similar among different ascertainment classes, suggesting that there is no dramatic effect of parental origin of the additional X chromosome on the phenotype of 47,XXY males.

Molecular studies of the parental origin and nature of human X isochromosomes

X-chromosome restriction fragment length polymorphisms were used to determine the parental origin of the isochromosome in nine individuals with an i(Xq) or idic(Xq). We were able to specify the parental source of eight of the nine isochromosomes, with six being maternal and two paternal in origin. In two cases, one i(Xq) and one idic(Xq), we used Xq markers to determine the level of heterozygosity in the isochromosome. Each was homozygous at all tested loci, suggesting that each originated from a single X chromosome and not from an exchange of material between two X's.