Chromothripsis in healthy individuals affects multiple protein-coding genes and can result in severe congenital abnormalities in offspring.

Chromothripsis represents an extreme class of complex chromosome rearrangements (CCRs) with major effects on chromosomal architecture. Although recent studies have associated chromothripsis with congenital abnormalities, the incidence and pathogenic effects of this phenomenon require further investigation. Here, we analyzed the genomes of three families in which chromothripsis rearrangements were transmitted from a mother to her child. The chromothripsis in the mothers resulted in completely balanced rearrangements involving 8-23 breakpoint junctions across three to five chromosomes. Two mothers did not show any phenotypic abnormalities, although 3-13 protein-coding genes were affected by breakpoints. Unbalanced but stable transmission of a subset of the derivative chromosomes caused apparently de novo complex copy-number changes in two children. This resulted in gene-dosage changes, which are probably responsible for the severe congenital phenotypes of these two children. In contrast, the third child, who has a severe congenital disease, harbored all three chromothripsis chromosomes from his healthy mother, but one of the chromosomes acquired de novo rearrangements leading to copy-number changes. These results show that the human genome can tolerate extreme reshuffling of chromosomal architecture, including breakage of multiple protein-coding genes, without noticeable phenotypic effects. The presence of chromothripsis in healthy individuals affects reproduction and is expected to substantially increase the risk of miscarriages, abortions, and severe congenital disease.

Genomic and transcriptomic plasticity in treatment-naive ovarian cancer.

Intra-tumor heterogeneity is a hallmark of many cancers and may lead to therapy resistance or interfere with personalized treatment strategies. Here, we combined topographic mapping of somatic breakpoints and transcriptional profiling to probe intra-tumor heterogeneity of treatment-naïve stage IIIC/IV epithelial ovarian cancer. We observed that most substantial differences in genomic rearrangement landscapes occurred between metastases in the omentum and peritoneum versus tumor sites in the ovaries. Several cancer genes such as NF1, CDKN2A, and FANCD2 were affected by lesion-specific breakpoints. Furthermore, the intra-tumor variability involved different mutational hallmarks including lesion-specific kataegis (local mutation shower coinciding with genomic breakpoints), rearrangement classes, and coding mutations. In one extreme case, we identified two independent TP53 mutations in ovary tumors and omentum/peritoneum metastases, respectively. Examination of gene expression dynamics revealed up-regulation of key cancer pathways including WNT, integrin, chemokine, and Hedgehog signaling in only subsets of tumor samples from the same patient. Finally, we took advantage of the multilevel tumor analysis to understand the effects of genomic breakpoints on qualitative and quantitative gene expression changes. We show that intra-tumor gene expression differences are caused by site-specific genomic alterations, including formation of in-frame fusion genes. These data highlight the plasticity of ovarian cancer genomes, which may contribute to their strong capacity to adapt to changing environmental conditions and give rise to the high rate of recurrent disease following standard treatment regimes.

The Diverse Effects of Complex Chromosome Rearrangements and Chromothripsis in Cancer Development.

In recent years, enormous progress has been made with respect to the identification of somatic mutations that contribute to cancer development. Mutation types range from small substitutions to large structural genomic rearrangements, including complex reshuffling of the genome. Sets of mutations in individual cancer genomes may show specific signatures, which can be provoked by both exogenous and endogenous forces. One of the most remarkable mutation patterns observed in human cancers involve massive rearrangement of just a few chromosomal regions. This phenomenon has been termed chromothripsis and appears widespread in a multitude of cancer types. Chromothripsis provides a way for cancer to rapidly evolve through a one-off massive change in genome structure as opposed to a gradual process of mutation and selection. This chapter focuses on the origin, prevalence and impact of chromothripsis and related complex genomic rearrangements during cancer development.

Distal spinal muscular atrophy featured by predominant calf muscle involvement in VRK1 associated disease - Case series and review.

We describe the shared clinical, biochemical, radiological and myopathological characteristics of four patients with distal spinal muscular atrophy (dSMA) caused by vaccinia-related kinase 1 (VRK1) variants and provide a review of the literature on phenotype-genotype correlations in VRK1-related disease. The clinical phenotype was characterized by adult-onset dSMA with predominant calf muscle involvement and mildly elevated serum creatinine kinase (CK) levels. Muscle imaging showed predominant atrophy and fatty replacement of calf muscles. We identified the novel compound heterozygous variants c.607C>T (p.Arg203Trp) and c.858G>T (p.Met286Ile) in two siblings with adult-onset dSMA. Additionally, two unrelated patients both carried the known c.583T>G (p.Leu195Val) VRK1 variant, with either c.197C>G (p.Ala66Gly) or c.701A>G (p.Asn234Ser) as a second variant. We conclude that compound heterozygous VRK1 variants cause distal spinal muscular atrophy with predominant posterior leg muscle involvement.

Lithium carbonate in amyotrophic lateral sclerosis patients homozygous for the C-allele at SNP rs12608932 in UNC13A: protocol for a confirmatory, randomized, group-sequential, event-driven, double-blind, placebo-controlled trial.

BACKGROUND: Given the large genetic heterogeneity in amyotrophic lateral sclerosis (ALS), it seems likely that genetic subgroups may benefit differently from treatment. An exploratory meta-analysis identified that patients homozygous for the C-allele at SNP rs12608932, a single nucleotide polymorphism in the gene UNC13A, had a statistically significant survival benefit when treated with lithium carbonate. We aim to confirm the efficacy of lithium carbonate on the time to death or respiratory insufficiency in patients with ALS homozygous for the C-allele at SNP rs12608932 in UNC13A. METHODS: A randomized, group-sequential, event-driven, double-blind, placebo-controlled trial will be conducted in 15 sites across Europe and Australia. Patients will be genotyped for UNC13A; those homozygous for the C-allele at SNP rs12608932 will be eligible. Patients must have a diagnosis of ALS according to the revised El Escorial criteria, and a TRICALS risk-profile score between -6.0 and -2.0. An expected number of 1200 patients will be screened in order to enroll a target sample size of 171 patients. Patients will be randomly allocated in a 2:1 ratio to lithium carbonate or matching placebo, and treated for a maximum duration of 24 months. The primary endpoint is the time to death or respiratory insufficiency, whichever occurs first. Key secondary endpoints include functional decline, respiratory function, quality of life, tolerability, and safety. An interim analysis for futility and efficacy will be conducted after the occurrence of 41 events. DISCUSSION: Lithium carbonate has been proven to be safe and well-tolerated in patients with ALS. Given the favorable safety profile, the potential benefits are considered to outweigh the burden and risks associated with study participation. This study may provide conclusive evidence about the life-prolonging potential of lithium carbonate in a genetic ALS subgroup. TRIAL REGISTRATION: EudraCT number 2020-000579-19 . Registered on 29 March 2021.

Micronuclei-based model system reveals functional consequences of chromothripsis in human cells.

Cancer cells often harbor chromosomes in abnormal numbers and with aberrant structure. The consequences of these chromosomal aberrations are difficult to study in cancer, and therefore several model systems have been developed in recent years. We show that human cells with extra chromosome engineered via microcell-mediated chromosome transfer often gain massive chromosomal rearrangements. The rearrangements arose by chromosome shattering and rejoining as well as by replication-dependent mechanisms. We show that the isolated micronuclei lack functional lamin B1 and become prone to envelope rupture, which leads to DNA damage and aberrant replication. The presence of functional lamin B1 partly correlates with micronuclei size, suggesting that the proper assembly of nuclear envelope might be sensitive to membrane curvature. The chromosomal rearrangements in trisomic cells provide growth advantage compared to cells without rearrangements. Our model system enables to study mechanisms of massive chromosomal rearrangements of any chromosome and their consequences in human cells.

The presence of extra chromosomes leads to genomic instability.

Aneuploidy is a hallmark of cancer and underlies genetic disorders characterized by severe developmental defects, yet the molecular mechanisms explaining its effects on cellular physiology remain elusive. Here we show, using a series of human cells with defined aneuploid karyotypes, that gain of a single chromosome increases genomic instability. Next-generation sequencing and SNP-array analysis reveal accumulation of chromosomal rearrangements in aneuploids, with break point junction patterns suggestive of replication defects. Trisomic and tetrasomic cells also show increased DNA damage and sensitivity to replication stress. Strikingly, we find that aneuploidy-induced genomic instability can be explained by the reduced expression of the replicative helicase MCM2-7. Accordingly, restoring near-wild-type levels of chromatin-bound MCM helicase partly rescues the genomic instability phenotypes. Thus, gain of chromosomes triggers replication stress, thereby promoting genomic instability and possibly contributing to tumorigenesis.

Chromosomal instability, tolerance of mitotic errors and multidrug resistance are promoted by tetraploidization in human cells.

Up to 80% of human cancers, in particular solid tumors, contain cells with abnormal chromosomal numbers, or aneuploidy, which is often linked with marked chromosomal instability. Whereas in some tumors the aneuploidy occurs by missegregation of one or a few chromosomes, aneuploidy can also arise during proliferation of inherently unstable tetraploid cells generated by whole genome doubling from diploid cells. Recent findings from cancer genome sequencing projects suggest that nearly 40% of tumors underwent whole genome doubling at some point of tumorigenesis, yet its contribution to cancer phenotypes and benefits for malignant growth remain unclear. Here, we investigated the consequences of a whole genome doubling in both cancerous and non-transformed p53 positive human cells. SNP array analysis and multicolor karyotyping revealed that induced whole-genome doubling led to variable aneuploidy. We found that chromosomal instability (CIN) is a frequent, but not a default outcome of whole genome doubling. The CIN phenotypes were accompanied by increased tolerance to mitotic errors that was mediated by suppression of the p53 signaling. Additionally, the expression of pro-apoptotic factors, such as iASPP and cIAP2, was downregulated. Furthermore, we found that whole genome doubling promotes resistance to a broad spectrum of chemotherapeutic drugs and stimulates anchorage-independent growth even in non-transformed p53-positive human cells. Taken together, whole genome doubling provides multifaceted benefits for malignant growth. Our findings provide new insight why genome-doubling promotes tumorigenesis and correlates with poor survival in cancer.