Molecular analysis of recombination in a family with Duchenne muscular dystrophy and a large pericentric X chromosome inversion.

It has been demonstrated in animal studies that, in animals heterozygous for pericentric chromosomal inversions, loop formation is greatly reduced during meiosis. This results in absence of recombination within the inverted segment, with recombination seen only outside the inversion. A recent study in yeast has shown that telomeres, rather than centromeres, lead in chromosome movement just prior to meiosis and may be involved in promoting recombination. We studied by cytogenetic analysis and DNA polymorphisms the nature of meiotic recombination in a three-generation family with a large pericentric X chromosome inversion, inv(X)(p21.1q26), in which Duchenne muscular dystrophy (DMD) was cosegregating with the inversion. On DNA analysis there was no evidence of meiotic recombination between the inverted and normal X chromosomes in the inverted segment. Recombination was seen at the telomeric regions, Xp22 and Xq27-28. No deletion or point mutation was found on analysis of the DMD gene. On the basis of the FISH results, we believe that the X inversion is the mutation responsible for DMD in this family. Our results indicate that (1) pericentric X chromosome inversions result in reduction of recombination between the normal and inverted X chromosomes; (2) meiotic X chromosome pairing in these individuals is likely initiated at the telomeres; and (3) in this family DMD is caused by the pericentric inversion.     

Recurrent proximal 18p monosomy and 18q trisomy in a family with a maternal pericentric inversion of chromosome 18

We report a recurrent partial monosomy of 18p10-->11.2 and proximal partial trisomy of 18q10-->21.3 caused by a maternal pericentric inversion of chromosome 18, involving breakpoints p11.2 and q21q21.3 Based on cytogenetics and FISH analysis, we speculate that the recurrent chromosome abnormality in the proband and in the fetus was the result of a translocation, possibly in a germ cell or germ cell precursor, between the maternal normal 18 and her inverted 18, resulting in maternal germinal mosaicism, i.e. 46,XX,inv(18)/46,XX,t[18;inv(18)][q10;q10]. The unbalanced karyotype of the proband and the fetus is 46,XY,+18,der[18;inv(18)][q10;q10]. To the best of our knowledge, there are no reports of this combination of proximal 18p monosomy and proximal 18q trisomy. The other interesting observation was association of Hirschsprung's disease in the proband.     

Correlation between chromosomal breakpoint positions and synaptic behaviour in human males heterozygous for a pericentric inversion

Summary The examination of synaptic data and localization of chromosomal breakpoints in a review of human pericentric inversions suggest that synaptic and recombination behaviour in rearranged chromosomes during meiosis can be predicted by determining the subband in which the breakpoint is located. According to this hypothesis, it can be postulated that loops in pericentric inversions are routinely formed only in cases when both breaks occur in G-light bands, whith the genetic consequences of crossing-over. In other cases, heterosynapsis is accomplished without previous homosynapsis, thereby minimizing the production of unbalanced gametes.     

Direct evidence for suppression of recombination within two pericentric inversions in humans: a new sperm-FISH technique.

Crossover within a pericentric inversion produces reciprocal recombinant chromosomes that are duplicated/deficient for all chromatin distal to the breakpoints. In view of this fact, a new technique is presented for estimating the frequency of recombination within pericentric inversions. YAC probes were selected from within the q- and p-arm flanking regions of two human inversions, and two-color FISH analysis was performed on sperm from heterozygous inversion carriers. A total of 6,006 sperm were analyzed for chromosome 1 inversion (p31q12), and 3,168 were analyzed for chromosome 8 inversion (p23q22). Both inversions displayed suppression of crossing-over, although the amount of suppression differed between the two inversions. The recombination frequency of 13.1% recorded for chromosome 8 inversion was similar to the frequency of 11.4% previously estimated by the human/hamster-fusion method. For chromosome 1 inversion, the recombination frequency of 0. 4% reported here was below the limits of detection of the fusion technique. The simplicity of the FISH technique and the ease of scoring facilitate analysis of a sample-population size much larger than previously had been possible.     

The Fertility Effects of Pericentric Inversions in Drosophila Melanogaster

Heterozygotes for pericentric inversions are expected to be semisterile because recombination in the inverted region produces aneuploid gametes. Newly arising pericentric inversions should therefore be quickly eliminated from populations by natural selection. The occasional polymorphism for such inversions and their fixation among closely related species have supported the idea that genetic drift in very small populations can overcome natural selection in the wild. We studied the effect of 7 second-chromosome and 30 third-chromosome pericentric inversions on the fertility of heterokaryotypic Drosophila melanogaster females. Surprisingly, fertility was not significantly reduced in many cases, even when the inversion was quite large. This lack of underdominance is almost certainly due to suppressed recombination in inversion heterozygotes, a phenomenon previously observed in Drosophila. In the large sample of third-chromosome inversions, the degree of underdominance depends far more on the position of breakpoints than on the inversion's length. Analysis of these positions shows that this chromosome has a pair of ``sensitive sites' near cytological divisions 68 and 92: these sites appear to reduce recombination in a heterozygous inversion whose breakpoints are nearby. There may also be ``sensitive sites' near divisions 31 and 49 on the second chromosome. Such sites may be important in initiating synapsis. Because many pericentric inversions do not reduce the fertility of heterozyotes, we conclude that the observed fixation or polymorphism of such rearrangements in nature does not imply genetic drift in very small populations.     

Recombination aneusomy of subtelomeric regions of chromosome 5, resulting from a large familial pericentric inversion inv(5)(p15.33q35.3)

We present a family with three cases of recombination aneusomy rec(5)dup(5q) originating from a large parental pericentric inversion of chromosome 5. The proband--a 6-year-old girl with mental retardation, speech delay, microcephaly, and slight facial dysmorphism--was referred for subtelomere testing. FISH with a Multiprobe Chromoprobe T System (CytoCell) and with several BAC clones mapping to both subtelomere regions of chromosome 5, revealed a recombinant chromosome rec(5)dup(5q) originating from a paternal pericentric inversion inv(5)(p15.33q35.3). The same inversion was present in the proband's father's twin-brother and rec(5)dup(5q) was also identified in his two mentally retarded daughters. The distance of breakpoints from the telomere was: 0.234-1.4 Mb for 5p and 4.1-4.8 Mb for 5q. HR-CGH analysis confirmed the duplication of the 5q subtelomeric region but did not identify any concomitant deletion in the 5p subtelomere. Precise mapping of the aneusomic regions in the proband enabled mapping the cat cry and speech delay to 5p15.33, making the earlier localizations of these features more precise. Our family shows that the large pericentric inversion with both breakpoints at subtelomeric regions of chromosome 5 is associated with a high risk of rec(5)dup(5q) in the progeny.     

Characterization of the human lineage-specific pericentric inversion that distinguishes human chromosome 1 from the homologous chromosomes of the great apes

The human and chimpanzee genomes are distinguishable in terms of ten gross karyotypic differences including nine pericentric inversions and a chromosomal fusion. Seven of these large pericentric inversions are chimpanzee-specific whereas two of them, involving human chromosomes 1 and 18, were fixed in the human lineage after the divergence of humans and chimpanzees. We have performed detailed molecular and computational characterization of the breakpoint regions of the human-specific inversion of chromosome 1. FISH analysis and sequence comparisons together revealed that the pericentromeric region of HSA 1 contains numerous segmental duplications that display a high degree of sequence similarity between both chromosomal arms. Detailed analysis of these regions has allowed us to refine the p-arm breakpoint region to a 154.2 kb interval at 1p11.2 and the q-arm breakpoint region to a 562.6 kb interval at 1q21.1. Both breakpoint regions contain human-specific segmental duplications arranged in inverted orientation. We therefore propose that the pericentric inversion of HSA 1 was mediated by intra-chromosomal non-homologous recombination between these highly homologous segmental duplications that had themselves arisen only recently in the human lineage by duplicative transposition.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .Justyna M. Szamalek and Violaine Goidts are contributed equally to the paper.     

The significance of pericentric inversions of chromosome 2

Summary Thirteen new cases of a pericentric inversion 2 collected from different laboratories are reported. In addition 41 cases of a pericentric inversion 2 were reviewed from the literature. The pooled data were analysed using Weinberg's proband method to evaluate the risk of a carrier for either children with congenital anomalies or reproductive wastage. In the corrected sample of 166 lifeborn offspring of carriers of a pericentric inversion 2 there were five who showed phenotypic anomalies and two died a few hours after delivery. The reported anomalies are heterogeneous and probably reflect the basic risk of any couple for abnormal lifeborn offspring. There has been no observation of a lifeborn who inherited an unbalanced recombination of a parental pericentric inversion 2. A carrier of a pericentric inversion 2 obviously has an increased risk for reproductive wastage. This is indicated by (1) an increase of the rate of spontaneous abortions and (2) an increase of the rate of index patients ascertained because of previous miscarriages. The risk of a carrier of a pericentric inversion 2 for a spontaneous abortion or a stillbirth may be about twice the basic risk of the general population.     

Function and Assembly of DNA Looping,Clustering, and Microtubule Attachment Complexes within a Eukaryotic Kinetochore

The kinetochore is a complex protein–DNA assembly that provides the mechanical linkage between microtubules and the centromere DNA of each chromosome. Centromere DNA in all eukaryotes is wrapped around a unique nucleosome that contains the histone H3 variant CENP-A (Cse4p in Saccharomyces cerevisiae). Here, we report that the inner kinetochore complex (CBF3) is required for pericentric DNA looping at the Cse4p-containing nucleosome. DNA within the pericentric loop occupies a spatially confined area that is radially displaced from the interpolar central spindle. Microtubule-binding kinetochore complexes are not involved in pericentric DNA looping but are required for the geometric organization of DNA loops around the spindle microtubules in metaphase. Thus, the mitotic segregation apparatus is a composite structure composed of kinetochore and interpolar microtubules, the kinetochore, and organized pericentric DNA loops. The linkage of microtubule-binding to centromere DNA-looping complexes positions the pericentric chromatin loops and stabilizes the dynamic properties of individual kinetochore complexes in mitosis.     

Partial trisomy 20p resulting from a recombination of a familial pericentric inversion

Summary Recombination of an inherited pericentric inversion of chromosome 20 has given rise to a child with partial trisomy 20p. To our knowledge no previous familial inversions of this chromosome have been described in the literature.     

Two Down syndrome patients with rec(21),dupq,inv(21)(p11;q2109) from a familial pericentric inversion

Aneusomie de recombinaison arose from a familial pericentric inversion of a chromosome 21. Two female patients had a typical Down syndrome; one of them had slight psychomotor retardation. There was partial trisomy 21q2109----qter in these two patients but ZnCu SOD activity was normal.     

The construction of the first balancer chromosome for the Mediterranean fruit fly, Ceratitis capitata

The construction of the first balancer chromosome, FiM1, for the medfly Ceratitis capitata is described. This chromosome has three overlapping pericentric inversions and is marked with dominant and recessive mutations. The inversion breakpoints of FiM1 suppress recombination throughout the length of the fifth chromosome, allowing lethal mutations to be recovered and maintained. This chromosome will provide a powerful tool for the manipulation of laboratory stocks, in particular, the recovery of new mutant and transgenic strains. We demonstrate the use of FiM1 for the recovery and maintenance of chromosomes carrying lethal mutations.     

Refined physical and genetic mapping of the NF1 region on chromosome 17.

A total of 15 polymorphic markers were used to construct a genetic map that encompasses the NF1 locus on chromosome 17. The markers were a subset of a large collection of chromosome 17-specific probes and were selected for marker typing in NF1 families after physical localization to the pericentric region of the chromosome. Multilocus data for a total of 17 informative NF1 families and 39 other families were included in genetic analyses. No recombination was observed between NF1 and four markers, one or more of which was informative in 86% of parents. More-refined physical mapping studies demonstrated that all four of the markers are proximal to the chromosome 17 translocation breakpoints from two NF1 patients bearing balanced translocations. The region flanking the disease locus spans a distance of 1 centimorgan (cM) in males and 9 cM in females. Close flanking markers were informative in 76% of meioses. Sex differences in recombination rates in the pericentric region were highly significant statistically.     

A second case of inv(4)pat with both recombinants in the offspring: rec dup(4q) in a girl with Wolf-Hirschhorn syndrome and rec dup(4p)

In a girl presenting with features of Wolf-Hirschhorn syndrome, cytogenetic and molecular cytogenetic analysis revealed a rearranged chromosome 4 with monosomy of the distal bands 4pter-->4p16.2 and trisomy of the distal bands 4q35.1-->4qter [rec dup(4q)] due to a large, paternal pericentric inversion. In the following two pregnancies, prenatal diagnosis showed the same imbalance in one fetus and a reverse segmental imbalance [rec dup(4p)] in the other. We discuss the recombination risk of the given inversion with respect to the size of the inverted segment and the viability of the recombinants. The high frequency of recombinants in this family and others suggests a high recurrence risk in similar cases with large pericentric inversions comprising almost entire chromosomes.     

Molecular analysis of a case of meiotic recombination leading to cri-du-chat syndrome

This paper describes a molecular investigation of a woman with an apparent large pericentric inversion of chromosome 5, inv(5)(p14;q35), and one normal chromosome 5 and her child, who was born with cri-du-chat syndrome. The four chromosome 5 homologs from the proband and his mother were isolated in somatic cell hybrids, and their haplotypes were determined at nine loci polymorphic for restriction enzyme sites. The deleted chromosome in the proband was shown to carry alleles from both maternal homologs, verifying molecularly that a meiotic recombination event in the mother gave rise to her son's deleted chromosome 5. The single crossover was presumably near the centromere.     

Meiotic analysis of a pericentric inversion, inv(7) (p22q32), in the father of a child with a duplication-deletion of chromosome 7

In a family in which a large pericentric inversion of chromosome 7 is segregating, two of the four progeny of inversion heterozygotes show severe psychomotor retardation and have the karyotype 46,XX,rec(7),dup q,inv(7)(p22q32), derived from crossing-over within the inversion. Meiotic analysis in one of the heterozygotes revealed no evidence of inversion loops in well-spread pachytene cells. In approximately 20% of cells in diakinesis, the presumptive bivalent 7 had only one chiasma. Two alternatives to the reversed loop mode of meiotic pairing of inversions are proposed. Review of the literature supports the view that "small" pericentric inversions have a much better genetic prognosis than "large" pericentric inversions.     

A new case of partial 14q31.3-qter trisomy due to maternal pericentric inversion

Chromosome 14 is often involved in chromosome rearrangements, although pericentric inversions are rare. Here we report a mother carrying a pericentric inversion of chromosome 14, and her daughter with recombinant chromosome characterized by a partial distal 14q trisomy. Principal clinical findings of the child include facial anomalies, microcephaly, developmental delay, hypotonia and cardiac malformation. Her final karyotype was 46,XX,rec(14)dup(14q)inv(14)(p12q31)mat[20], arr 14q31.3qter(85,427,839–106,356,482)x3. This report brings new data about clinical features of partial 14q trisomy and molecular analysis enables the visualization of genes involved in the segment duplicated.     

Pure trisomy 17p in 60% of cells

Summary A patient with pure trisomy of the short arm of chromosome 17 in 60% of the examined cells is reported. She presented a variant chromosome 1 with partial pericentric inversion and increased centromeric heterochromatin in one chromosome 17. The cytogenetic findings are discussed. The clinical findings are compared to those found in other reported cases of partial trisomy 17 and a delineation of a pure trisomy 17p attempted.     

Genetic analysis of meiotic recombination in humans by use of sperm typing: reduced recombination within a heterozygous paracentric inversion of chromosome 9q32-q34.3.

To investigate patterns of genetic recombination within a heterozygous paracentric inversion of chromosome 9 (46XY inv[9] [q32q34.3]), we performed sperm typing using a series of polymorphic microsatellite markers spanning the inversion region. For comparison, two donors with cytogenetically normal chromosomes 9, one of whom was heterozygous for a pericentric chromosome 2 inversion (46XY inv[2] [p11q13]), were also tested. Linkage analysis was performed by use of the multilocus linkage-analysis program SPERM, and also CRI-MAP, which was adapted for sperm-typing data. Analysis of the controls generated a marker order in agreement with previously published data and revealed no significant interchromosomal effects of the inv(2) on recombination on chromosome 9. FISH employing cosmids containing appropriate chromosome 9 markers was used to localize the inversion breakpoint of inv(9). Analysis of inv(9) sperm was performed by use of a set of microsatellite markers that mapped centromeric to, telomeric to, and within the inversion breakpoints. Three distinct patterns of recombination across the region were observed. Proximal to the centromeric breakpoint, recombination was similar to normal levels. Distal to the telomeric breakpoint, there was an increase in recombination found in the inversion patient. Finally, within the inversion, recombination was dramatically reduced, but several apparent double recombinants were found. A putative model explaining these data is proposed.