FoSTeS, MMBIR and NAHR at the human proximal Xp region and the mechanisms of human Xq isochromosome formation.

Department of Medical Genetics, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands.
Human Molecular Genetics (Impact Factor: 7.69). 02/2011; 20(10):1925-36. DOI: 10.1093/hmg/ddr074
Source: PubMed

ABSTRACT The recently described DNA replication-based mechanisms of fork stalling and template switching (FoSTeS) and microhomology-mediated break-induced replication (MMBIR) were previously shown to catalyze complex exonic, genic and genomic rearrangements. By analyzing a large number of isochromosomes of the long arm of chromosome X (i(Xq)), using whole-genome tiling path array comparative genomic hybridization (aCGH), ultra-high resolution targeted aCGH and sequencing, we provide evidence that the FoSTeS and MMBIR mechanisms can generate large-scale gross chromosomal rearrangements leading to the deletion and duplication of entire chromosome arms, thus suggesting an important role for DNA replication-based mechanisms in both the development of genomic disorders and cancer. Furthermore, we elucidate the mechanisms of dicentric i(Xq) (idic(Xq)) formation and show that most idic(Xq) chromosomes result from non-allelic homologous recombination between palindromic low copy repeats and highly homologous palindromic LINE elements. We also show that non-recurrent-breakpoint idic(Xq) chromosomes have microhomology-associated breakpoint junctions and are likely catalyzed by microhomology-mediated replication-dependent recombination mechanisms such as FoSTeS and MMBIR. Finally, we stress the role of the proximal Xp region as a chromosomal rearrangement hotspot.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose:Turner syndrome is a developmental disorder caused by partial or complete monosomy for the X chromosome in 1 in 2,500 females. We hypothesized that single-nucleotide polymorphism (SNP) array genotyping could provide superior resolution in comparison to metaphase karyotype analysis to facilitate genotype-phenotype correlations.Methods:We genotyped 187 Turner syndrome patients with 733,000 SNP marker arrays. All cases met diagnostic criteria for Turner syndrome based on karyotypes (60%) or characteristic physical features. The SNP array results confirmed the diagnosis of Turner syndrome in 100% of cases.Results:We identified a single X chromosome (45,X) in 113 cases. In 58 additional cases (31%), other mosaic cell lines were present, including isochromosomes (16%), rings (5%), and Xp deletions (8%). The remaining cases were mosaic for monosomy X and normal male or female cell lines. Array-based models of X chromosome structure were compatible with karyotypes in 104 of 116 comparable cases (90%). We found that the SNP array data did not detect X-autosome translocations (three cases) but did identify two derivative Y chromosomes and 13 large copy-number variants that were not detected by karyotyping.Conclusion:Our study is the first systematic comparison between the two methods and supports the utility of SNP array genotyping to address clinical and research questions in Turner syndrome.Genet Med advance online publication 6 June 2013Genetics in Medicine (2013); doi:10.1038/gim.2013.77.
    Genetics in medicine: official journal of the American College of Medical Genetics 06/2013; · 3.92 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Whole-genome oligonucleotide single-nucleotide polymorphism (oligo-SNP) arrays enable simultaneous interrogation of copy number variations (CNVs), copy neutral regions of homozygosity (ROH) and uniparental disomy (UPD). Structural variation in the human genome contributes significantly to genetic variation, and often has deleterious effects leading to disease causation. Co-occurrence of CNV and regions of allelic homozygosity in tandem involving the same chromosomal arm are extremely rare. Replication-based mechanisms such as microhomology-mediated break-induced replication (MMBIR) are recent models predicted to induce structural rearrangements and gene dosage aberrations; however, supportive evidence in humans for one-ended DNA break repair coupled with MMBIR giving rise to interstitial copy number gains and distal loss of heterozygosity has not been documented. We report on the identification and characterization of two cases with interstitial triplication followed by uniparental isodisomy (isoUPD) for remainder of the chromosomal arm. Case 1 has a triplication at 9q21.11-q21.33 and segmental paternal isoUPD for 9q21.33-qter, and presented with citrullinemia with a homozygous mutation in the argininosuccinate synthetase gene (ASS1 at 9q34.1). Case 2 has a triplication at 22q12.1-q12.2 and segmental maternal isoUPD 22q12.2-qter, and presented with hearing loss, mild dysmorphic features and bilateral iris coloboma. Interstitial triplication coupled with distal segmental isoUPD is a novel finding that provides human evidence for one-ended DNA break and replication-mediated repair. Both copy number gains and isoUPD may contribute to the phenotype. Significantly, these cases represent the first detailed genomic analysis that provides support for a MMBIR mechanism inducing copy number gains and segmental isoUPD in tandem.European Journal of Human Genetics advance online publication, 9 April 2014; doi:10.1038/ejhg.2014.53.
    European journal of human genetics: EJHG 04/2014; · 3.56 Impact Factor
  • Journal of genetics. 04/2014; 93(1):189-92.

Full-text (2 Sources)

Available from
May 16, 2014