Allele-Specific HLA Loss and Immune Escape in Lung Cancer Evolution.

Immune evasion is a hallmark of cancer. Losing the ability to present neoantigens through human leukocyte antigen (HLA) loss may facilitate immune evasion. However, the polymorphic nature of the locus has precluded accurate HLA copy-number analysis. Here, we present loss of heterozygosity in human leukocyte antigen (LOHHLA), a computational tool to determine HLA allele-specific copy number from sequencing data. Using LOHHLA, we find that HLA LOH occurs in 40% of non-small-cell lung cancers (NSCLCs) and is associated with a high subclonal neoantigen burden, APOBEC-mediated mutagenesis, upregulation of cytolytic activity, and PD-L1 positivity. The focal nature of HLA LOH alterations, their subclonal frequencies, enrichment in metastatic sites, and occurrence as parallel events suggests that HLA LOH is an immune escape mechanism that is subject to strong microenvironmental selection pressures later in tumor evolution. Characterizing HLA LOH with LOHHLA refines neoantigen prediction and may have implications for our understanding of resistance mechanisms and immunotherapeutic approaches targeting neoantigens. VIDEO ABSTRACT.

Somatic mutations in arteriovenous malformations in hereditary hemorrhagic telangiectasia support a bi-allelic two-hit mutation mechanism of pathogenesis.

Hereditary hemorrhagic telangiectasia (HHT) is an inherited disorder of vascular malformations characterized by mucocutaneous telangiectases and arteriovenous malformations (AVMs) in internal organs. HHT is caused by inheritance of a loss of function mutation in one of three genes. Although individuals with HHT are haploinsufficient for one of these genes throughout their entire body, rather than exhibiting a systemic vascular phenotype, vascular malformations occur as focal lesions in discrete anatomic locations. The inconsistency between genotype and phenotype has provoked debate over whether haploinsufficiency or a different mechanism gives rise to the vascular malformations. We previously showed that HHT-associated skin telangiectases develop by a two-hit mutation mechanism in an HHT gene. However, somatic mutations were identified in only half of the telangiectases, raising the question whether a second-hit somatic mutation is a necessary (required) event in HHT pathogenesis. Here, we show that another mechanism for the second hit is loss of heterozygosity across the chromosome bearing the germline mutation. Secondly, we investigate the two-hit mutation mechanism for internal organ AVMs, the source of much of the morbidity of HHT. Here, we identified somatic molecular genetic events in eight liver telangiectases, including point mutations and a loss of heterozygosity event. We also identified somatic mutations in one pulmonary AVM and two brain AVMs, confirming that mucocutaneous and internal organ vascular malformations undergo the same molecular mechanisms. Together, these data argue that bi-allelic loss of function in an HHT gene is a required event in the pathogenesis of HHT-associated vascular malformations.

Variants in ATRIP are associated with breast cancer susceptibility in the Polish population and UK Biobank.

Several breast cancer susceptibility genes have been discovered, but more are likely to exist. To identify additional breast cancer susceptibility genes, we used the founder population of Poland and performed whole-exome sequencing on 510 women with familial breast cancer and 308 control subjects. We identified a rare mutation in ATRIP (GenBank: NM_130384.3: c.1152_1155del [p.Gly385Ter]) in two women with breast cancer. At the validation phase, we found this variant in 42/16,085 unselected Polish breast cancer-affected individuals and in 11/9,285 control subjects (OR = 2.14, 95% CI = 1.13-4.28, p = 0.02). By analyzing the sequence data of the UK Biobank study participants (450,000 individuals), we identified ATRIP loss-of-function variants among 13/15,643 breast cancer-affected individuals versus 40/157,943 control subjects (OR = 3.28, 95% CI = 1.76-6.14, p < 0.001). Immunohistochemistry and functional studies showed the ATRIP c.1152_1155del variant allele is weakly expressed compared to the wild-type allele, and truncated ATRIP fails to perform its normal function to prevent replicative stress. We showed that tumors of women with breast cancer who have a germline ATRIP mutation have loss of heterozygosity at the site of ATRIP mutation and genomic homologous recombination deficiency. ATRIP is a critical partner of ATR that binds to RPA coating single-stranded DNA at sites of stalled DNA replication forks. Proper activation of ATR-ATRIP elicits a DNA damage checkpoint crucial in regulating cellular responses to DNA replication stress. Based on our observations, we conclude ATRIP is a breast cancer susceptibility gene candidate linking DNA replication stress to breast cancer.

Global genomic instability caused by reduced expression of DNA polymerase ε in yeast.

SignificanceAlthough most studies of the genetic regulation of genome stability involve an analysis of mutations within the coding sequences of genes required for DNA replication or DNA repair, recent studies in yeast show that reduced levels of wild-type enzymes can also produce a mutator phenotype. By whole-genome sequencing and other methods, we find that reduced levels of the wild-type DNA polymerase ε in yeast greatly increase the rates of mitotic recombination, aneuploidy, and single-base mutations. The observed pattern of genome instability is different from those observed in yeast strains with reduced levels of the other replicative DNA polymerases, Pol α and Pol δ. These observations are relevant to our understanding of cancer and other diseases associated with genetic instability.

Abnormal biomarkers predict complex FAS or FADD defects missed by exome sequencing.

BACKGROUND: Elevated TCRαß+CD4-CD8- double-negative T cells (DNT) and serum biomarkers help identify FAS mutant patients with autoimmune lymphoproliferative syndrome (ALPS). However, in some patients with clinical features and biomarkers consistent with ALPS, germline or somatic FAS mutations cannot be identified on standard exon sequencing (ALPS-undetermined: ALPS-U). OBJECTIVE: We sought to explore whether complex genetic alterations in the FAS gene escaping standard sequencing or mutations in other FAS pathway-related genes could explain these cases. METHODS: Genetic analysis included whole FAS gene sequencing, copy number variation analysis, and sequencing of FAS cDNA and other FAS pathway-related genes. It was guided by FAS expression analysis on CD57+DNT, which can predict somatic loss of heterozygosity (sLOH). RESULTS: Nine of 16 patients with ALPS-U lacked FAS expression on CD57+DNT predicting heterozygous "loss-of-expression" FAS mutations plus acquired somatic second hits in the FAS gene, enriched in DNT. Indeed, 7 of 9 analyzed patients carried deep intronic mutations or large deletions in the FAS gene combined with sLOH detectable in DNT; 1 patient showed a FAS exon duplication. Three patients had reduced FAS expression, and 2 of them harbored mutations in the FAS promoter, which reduced FAS expression in reporter assays. Three of the 4 ALPS-U patients with normal FAS expression carried heterozygous FADD mutations with sLOH. CONCLUSION: A combination of serum biomarkers and DNT phenotyping is an accurate means to identify patients with ALPS who are missed by routine exome sequencing.

CRISPR/Cas gene editing in the human germline.

The ease and efficacy of CRISPR/Cas9 germline gene editing in animal models paved the way to human germline gene editing (HGGE), by which permanent changes can be introduced into the embryo. Distinct genes can be knocked out to examine their function during embryonic development. Alternatively, specific sequences can be introduced which can be applied to correct disease-causing mutations. To date, it has been shown that the success of HGGE is dependent on various experimental parameters and that various hurdles (i.e. loss-of-heterozygosity and mosaicism) need to be overcome before clinical applications should be considered. Due to the shortage of human germline material and the ethical constraints concerning HGGE, alternative models such as stem cells have been evaluated as well, in terms of their predictive value on the genetic outcome for HGGE approaches. This review will give an overview of the state of the art of HGGE in oocytes and embryos, and its accompanying challenges.

Telomere length and clonal chromosomal alterations in peripheral blood of patients with severe aplastic anaemia.

Severe aplastic anaemia (SAA) is a rare and life-threatening bone marrow failure disorder. We used data from the transplant outcomes in aplastic anaemia study to characterize mosaic chromosomal alterations (mCAs) in the peripheral blood of 738 patients with acquired SAA and evaluate their associations with telomere length (TL) and survival post-haematopoietic cell transplant (HCT). The median age at HCT was 20.4 years (range = 0.2-77.4). Patients with SAA had shorter TL than expected for their age (median TL percentile for age: 35.7th; range <1-99.99). mCAs were detected in 211 patients (28.6%), with chr6p copy-neutral loss of heterozygosity (6p-CNLOH) in 15.9% and chr7 loss in 3.0% of the patients; chrX loss was detected in 4.1% of female patients. Negative correlations between mCA cell fraction and measured TL (r = -0.14, p = 0.0002), and possibly genetically predicted TL (r = -0.07, p = 0.06) were noted. The post-HCT 3-year survival probability was low in patients with chr7 loss (39% vs. 72% in patients with chr6-CNLOH, 60% in patients with other mCAs and 70% in patients with no mCAs; p-log rank = 0.001). In multivariable analysis, short TL (p = 0.01), but not chr7 loss (p = 0.29), was associated with worse post-HCT survival. TL may guide clinical decisions in patients with SAA.

A case of hepatitis-associated aplastic anaemia following living-donor liver transplantation for fulminant hepatitis showing loss of heterozygosity in the 6p chromosome in the affected liver.

The mechanisms underlying hepatitis-associated aplastic anaemia (HAAA) that occurs several weeks after the development of acute hepatitis are unknown. A 20-year-old male developed HAAA following living-donor liver transplantation for fulminant hepatitis. The patient's leucocytes lacked HLA-class I due to loss of heterozygosity in the short arm of chromosome 6p (6pLOH). Interestingly, the patient's liver cells resected during the transplantation also exhibited 6pLOH that affected the same HLA haplotype as the leucocytes, suggesting that CD8+ T cells recognizing antigens presented by specific HLA molecules on liver cells may have attacked the haematopoietic stem cells of the patient, leading to the HAAA development.

Multi-locus sequence typing and phylogenetics of Cryptococcus neoformans AD hybrids.

Hybrid AD strains of the human pathogenic Cryptococcus neoformans species complex have been reported from many parts of the world. However, their origin, diversity, and evolution are incompletely understood. In this study, we analyzed 102 AD hybrid strains representing 21 countries on five continents. For each strain, we obtained its mating type and its allelic sequences at each of the seven loci that have been used for genotyping haploid serotypes A and D strains of the species complex by the Cryptococcus research community. Our results showed that most AD hybrids exhibited loss of heterozygosity at one or more of the seven analyzed loci. Phylogenetic and population genetic analyses of the allelic sequences revealed multiple origins of the hybrids within each continent, dating back to one million years ago in Africa and up to the present in other continents. We found evidence for clonal reproduction and long-distance dispersal of these hybrids in nature. Comparisons with the global haploid serotypes A and D strains identified new alleles and new haploid multi-locus genotypes in AD hybrids, consistent with the presence of yet-to-be discovered genetic diversity in haploid populations of this species complex in nature. Together, our results indicate that AD hybrids can be effectively genotyped using the same multi-locus sequencing type approach as that established for serotypes A and D strains. Our comparisons of the AD hybrids among each other as well as with the global haploid serotypes A and D strains revealed novel genetic diversity as well as evidence for multiple origins and dynamic evolution of these hybrids in nature.

A Gradual Transition Toward Anaplasia in Wilms Tumor Through Tolerance to Genetic Damage.

Patients with Wilms tumor (WT) in general have excellent survival, but the prognosis of patients belonging to the subgroup of WT with diffuse anaplasia (DA) is poor due to frequent resistance to chemotherapy. We hypothesized that DA WT cells might undergo changes, such as acquiring a persistent tolerance to DNA damage and copy number aberrations (CNAs), which could eventually lead to their resistance to chemotherapy treatment. Tissue sections from chemotherapy-treated DA WTs (n = 12) were compared with chemotherapy-treated nonanaplastic WTs (n = 15) in a tissue microarray system, enabling analysis of 769 tumor regions. All regions were scored for anaplastic features and immunohistochemistry was used to quantify p53 expression, proliferation index (Ki67), and DNA double-strand breaks (γH2AX). CNAs were assessed by array-based genotyping and TP53 mutations using targeted sequencing. Proliferation index and the frequency of DNA double-strand breaks (γH2AX dot expression) increased with higher anaplasia scores. Almost all (95.6%) areas with full-scale anaplasia had TP53 mutations or loss of heterozygosity, along with an increased amount of CNAs. Interestingly, areas with wild-type TP53 with loss of heterozygosity and only one feature of anaplasia (anaplasia score 1) also had significantly higher proliferation indices, more DNA double-strand breaks, and more CNAs than regions without any anaplastic features (score 0); such areas may be preanaplastic cell populations under selective pressure for TP53 mutations. In conclusion, we suggest that chemoresistance of DA WTs may be partly explained by a high proliferative capability of anaplastic cells, which also have a high burden of double-stranded DNA breaks and CNAs, and that there is a gradual emergence of anaplasia in WT.

Validation of a targeted next-generation sequencing panel for pancreatic ductal adenocarcinomas.

Pancreatic ductal adenocarcinoma (PDAC) is reported to be amongst the cancers with the lowest survival rate at 5 years. In the present study we aimed to validate a targeted next-generation sequencing (tNGS) panel to use in clinical routine, investigating genes important for PDAC diagnostic, prognostic and potential theragnostic aspect. In this NGS panel we also designed target regions to inquire about loss of heterozygosity (LOH) of chromosome 18 that has been described to be possibly linked to a worse disease progression. Copy number alteration has also been explored for a subset of genes. The last two methods are not commonly used for routine diagnostic with tNGS panels and we investigated their possible contribution to better characterize PDAC. A series of 140 formalin-fixed paraffin-embedded (FFPE) PDAC samples from 140 patients was characterized using this panel. Ninety-two % of patients showed alterations in at least one of the investigated genes (most frequent KRAS, TP53, SMAD4, CDKN2A and RNF43). Regarding LOH evaluation, we were able to detect chr18 LOH starting at 20% cell tumor percentage. The presence of LOH on chr18 is associated with a worse disease- and metastasis-free survival, in uni- and multivariate analyses. The present study validates the use of a tNGS panel for PDAC characterization, also evaluating chr18 LOH status for prognostic stratification.

Origin of Residual Tumor Masses in BRCA1/2-Driven Ovarian Carcinomas Treated by Neoadjuvant Chemotherapy: Selection of Preexisting BRCA1/2-Proficient Tumor Cells but Not the Gain of Second ORF-Restoring Mutation.

INTRODUCTION: Tubo-ovarian carcinomas (OCs) are highly sensitive to platinum-based neoadjuvant chemotherapy (NACT) but almost never demonstrate complete pathologic response. METHODS: We analyzed paired primary and residual tumor tissues from 30 patients with hereditary BRCA1/2-driven OCs (BRCA1: 17; BRCA2: 13), who were treated by carboplatin/paclitaxel NACT (median number of cycles: 3, range: 3-6). BRCA1/2 and TP53 genes were analyzed by the next-generation sequencing. The ratio between TP53 mutation-specific versus wild-type reads was considered to monitor the proportion of tumor and non-tumor cells in the tissue sample, and the ratio between BRCA1/2-mutated and wild-type reads was used to estimate the presence of cells with the loss or retention of heterozygosity (LOH or ROH, respectively). RESULTS: All 30 OCs had BRCA1/2 LOH in primary tumor and carried somatic TP53 mutation. Twenty-eight OCs had sufficient tumor cell cellularity in the post-NACT tissue to evaluate the ratio between mutated and wild-type BRCA1/2 alleles. Five (18%) out of 28 informative tumor pairs showed transition from LOH to ROH during NACT presumably affecting all or the vast majority of residual tumor cells. There were no signals of the emergence of a second open reading frame-restoring BRCA1/2 mutation. CONCLUSION: Chemonaive BRCA1/2-driven carcinomas may contain a fraction of tumor cells with preserved BRCA1/2 heterozygosity. NACT can cause a selection of pre-existing BRCA1/2-proficient tumor cells, without gaining secondary reversal BRCA1/2 mutations.

Prevalence of homologous recombination biomarkers in multiple tumor types: an observational study.

Aim: To determine the prevalence of deleterious mutations in BRCA1 and BRCA2 and in 13 genes involved in homologous recombination repair (HRR), the prevalence of genomic loss of heterozygosity and the allelic and hereditary status of BRCA1, BRCA2 and other HRR gene mutations in multiple solid tumor types. Patients & methods: This was a retrospective observational study of patients with an advanced/metastatic diagnosis in one of 15 solid tumor types, who were identified in a real-world clinico-genomic database. Results: Tumor tissue samples from 9457 patients were analyzed, among which 4.7% had known or suspected deleterious BRCA1/2 mutations. The prevalence (range) of mutations in HRR genes was 13.6% (2.4%-26.0%) and genomic loss of heterozygosity ≥16% was 20.6% (2.6-34.4%) across all tumor types. Conclusion: The prevalence of mutations varied significantly depending on the type of tumor.

The integrity of the human genome is maintained via multiple pathways of DNA repair, one of the most important of which is homologous recombination repair (HRR), which uses a sister chromatid as a template for high-fidelity restoration of altered DNA sequences. This study aimed to determine the prevalence of deleterious mutations, i.e., changes in the genetic code that interfere with proper cellular function, in the breast cancer genes BRCA1 and BRCA2 and in 13 other genes involved in HRR in various types of solid tumors in patients with advanced or metastatic cancer. The researchers found that 4.7% of tumor samples had BRCA1/2 mutations, 13.6% had mutations in any of the HRR genes and 20.6% had genomic loss of heterozygosity (gLOH) of at least 16% i.e., loss of sections of chromosomes affecting 16% or more of the genome. BRCA1/2 mutations were most common in ovarian cancer (13.1%), prostate cancer (9.3%), breast cancer (8.2%) and pancreatic cancer (4.9%). Prevalence for mutations in HRR genes ranges from 2.4 to 26.0% and gLOH ≥16% ranged from 2.6 to 34.4% depending on the tumor type. In conclusion, the prevalence of mutations in the BRCA1/2 genes, HRR genes and gLOH ≥16% varied widely across 15 tumor types.

Targeting loss of heterozygosity for cancer-specific immunotherapy.

Developing therapeutic agents with potent antitumor activity that spare normal tissues remains a significant challenge. Clonal loss of heterozygosity (LOH) is a widespread and irreversible genetic alteration that is exquisitely specific to cancer cells. We hypothesized that LOH events can be therapeutically targeted by "inverting" the loss of an allele in cancer cells into an activating signal. Here we describe a proof-of-concept approach utilizing engineered T cells approximating NOT-gate Boolean logic to target counterexpressed antigens resulting from LOH events in cancer. The NOT gate comprises a chimeric antigen receptor (CAR) targeting the allele of human leukocyte antigen (HLA) that is retained in the cancer cells and an inhibitory CAR (iCAR) targeting the HLA allele that is lost in the cancer cells. We demonstrate that engineered T cells incorporating such NOT-gate logic can be activated in a genetically predictable manner in vitro and in mice to kill relevant cancer cells. This therapeutic approach, termed NASCAR (Neoplasm-targeting Allele-Sensing CAR), could, in theory, be extended to LOH of other polymorphic genes that result in altered cell surface antigens in cancers.

Frequent loss of heterozygosity in CRISPR-Cas9-edited early human embryos.

CRISPR-Cas9 genome editing is a promising technique for clinical applications, such as the correction of disease-associated alleles in somatic cells. The use of this approach has also been discussed in the context of heritable editing of the human germ line. However, studies assessing gene correction in early human embryos report low efficiency of mutation repair, high rates of mosaicism, and the possibility of unintended editing outcomes that may have pathologic consequences. We developed computational pipelines to assess single-cell genomics and transcriptomics datasets from OCT4 (POU5F1) CRISPR-Cas9-targeted and control human preimplantation embryos. This allowed us to evaluate on-target mutations that would be missed by more conventional genotyping techniques. We observed loss of heterozygosity in edited cells that spanned regions beyond the POU5F1 on-target locus, as well as segmental loss and gain of chromosome 6, on which the POU5F1 gene is located. Unintended genome editing outcomes were present in ∼16% of the human embryo cells analyzed and spanned 4-20 kb. Our observations are consistent with recent findings indicating complexity at on-target sites following CRISPR-Cas9 genome editing. Our work underscores the importance of further basic research to assess the safety of genome editing techniques in human embryos, which will inform debates about the potential clinical use of this technology.

Evolution of loss of heterozygosity patterns in hybrid genomes of Candida yeast pathogens.

BACKGROUND: Hybrids are chimeric organisms with highly plastic heterozygous genomes that may confer unique traits enabling the adaptation to new environments. However, most evolutionary theory frameworks predict that the high levels of genetic heterozygosity present in hybrids from divergent parents are likely to result in numerous deleterious epistatic interactions. Under this scenario, selection is expected to favor recombination events resulting in loss of heterozygosity (LOH) affecting genes involved in such negative interactions. Nevertheless, it is so far unknown whether this phenomenon actually drives genomic evolution in natural populations of hybrids. To determine the balance between selection and drift in the evolution of LOH patterns in natural yeast hybrids, we analyzed the genomic sequences from fifty-five hybrid strains of the pathogenic yeasts Candida orthopsilosis and Candida metapsilosis, which derived from at least six distinct natural hybridization events. RESULTS: We found that, although LOH patterns in independent hybrid clades share some level of convergence that would not be expected from random occurrence, there is an apparent lack of strong functional selection. Moreover, while mitosis is associated with a limited number of inter-homeologous chromosome recombinations in these genomes, induced DNA breaks seem to increase the LOH rate. We also found that LOH does not accumulate linearly with time in these hybrids. Furthermore, some C. orthopsilosis hybrids present LOH patterns compatible with footprints of meiotic recombination. These meiotic-like patterns are at odds with a lack of evidence of sexual recombination and with our inability to experimentally induce sporulation in these hybrids. CONCLUSIONS: Our results suggest that genetic drift is the prevailing force shaping LOH patterns in these hybrid genomes. Moreover, the observed LOH patterns suggest that these are likely not the result of continuous accumulation of sporadic events-as expected by mitotic repair of rare chromosomal breaks-but rather of acute episodes involving many LOH events in a short period of time.

Specific Deletions of Chromosomes 3p, 5q, 13q, and 21q among Patients with G2 Grade of Non-Small Cell Lung Cancer.

Non-small cell lung cancer (NSCLC) leads as a primary cause of cancer-related premature mortality in Western populations. This study leverages cutting-edge gene-expression-profiling technologies to perform an in-depth molecular characterization of NSCLC specimens, with the objective of uncovering tumor-specific genomic alterations. By employing DNA microarray analysis, our research aims to refine the classification of NSCLC for early detection, guide molecular-targeted treatment approaches, enhance prognostication, and broaden the scientific understanding of the disease's biology. We identified widespread genomic abnormalities in our samples, including the recurrent loss of chromosomal regions 3p, 5q, 13q, and 21q and the gain of 12p. Furthermore, utilizing Metascape for bioinformatic analysis revealed critical biological pathways disrupted in NSCLC, offering promising leads for novel therapeutic interventions.

Loss of Heterozygosity and Mutations in the RAS-ERK Pathway Genes in Tumor Cells of Various Loci in Multiple Myeloma.

Multiple myeloma (MM) is a disease characterized by spatiotemporal heterogeneity of tumor clones. Different genetic aberrations can be observed simultaneously in tumor cells from different loci, and as the disease progresses, new subclones may appear. The role of liquid biopsy, which is based on the analysis of tumor DNA circulating in the blood plasma, continues to be explored in MM. Here, we present an analysis of the STR profiles and mutation status of the KRAS, NRAS, and BRAF genes, evaluated in plasma free circulating tumor DNA (ctDNA), CD138+ bone marrow cells, and plasmacytomas. The prospective single-center study included 97 patients, with a median age of 55 years. Of these, 94 had newly diagnosed symptomatic MM, and three had primary plasma cell leukemia. It should be noted that if mutations were detected only in ctDNA, "non-classical" codons were more often affected. A variety of adverse laboratory and clinical factors have been associated with the detection of rare KRAS or NRAS gene mutations in bone marrow or ctDNA, suggesting that these mutations may be factors of an unfavorable prognosis for MM. Liquid biopsy studies provide undeniable fundamental information about tumor heterogeneity and clonal evolution in MM. Moreover, we focus on using liquid biopsy to identify new high-risk factors for MM.

Loss of Heterozygosity Spectrum Depends on Ploidy Level in Natural Yeast Populations.

The appearance of genomic variations such as loss of heterozygosity (LOH) has a significant impact on phenotypic diversity observed in a population. Recent large-scale yeast population genomic surveys have shown a high frequency of these events in natural isolates and more particularly in polyploids. However, the frequency, extent, and spectrum of LOH in polyploid organisms have never been explored and are poorly characterized to date. Here, we accumulated 5,163 LOH events over 1,875 generations in 76 mutation accumulation (MA) lines comprising nine natural heterozygous diploid, triploid, and tetraploid natural S. cerevisiae isolates from different ecological and geographical origins. We found that the rate and spectrum of LOH are variable across ploidy levels. Of the total accumulated LOH events, 8.5%, 21%, and 70.5% of them were found in diploid, triploid, and tetraploid MA lines, respectively. Our results clearly show that the frequency of generated LOH events increases with ploidy level. In fact, the cumulative LOH rates were estimated to be 9.3 × 10-3, 2.2 × 10-2, and 8.4 × 10-2 events per division for diploids, triploids, and tetraploids, respectively. In addition, a clear bias toward the accumulation of interstitial and short LOH tracts is observed in triploids and tetraploids compared with diploids. The variation of the frequency and spectrum of LOH events across ploidy level could be related to the genomic instability, characterizing higher ploidy isolates.

Autosomal dominant genodermatoses in adults being heralded by superimposed skin lesions in children.

In autosomal dominant skin disorders, pronounced mosaic involvement may sometimes occur in the neonate, originating in a heterozygous embryo from early loss of heterozygosity, probably during the first week after fertilization. In biallelic phenotypes, such overlaying mosaic involvement may coexist with disseminated mosaicism, for example, in neurofibromatosis or tuberous sclerosis. In other phenotypes, however, classical nonsegmental involvement tends to appear much later, which is why the superimposed mosaic is a heralding feature. In Brooke-Spiegler syndrome (eccrine cylindromatosis), a large pedigree documented a 5-year-old boy with multiple, congenital small eccrine cylindromas along the lines of Blaschko. Disseminated cylindromas were absent because they usually appear in adulthood. ̶ In Hornstein-Knickenberg syndrome, an affected woman had an 8-year-old son with a nevus comedonicus-like lesion exemplifying a forerunner of the syndrome. ("Birt-Hogg-Dubé syndrome" represents a nonsyndromic type of hereditary perifollicular fibromas.) In glomangiomatosis, neonatal superimposed mosaicism is a heralding feature because disseminated lesions appear during puberty or adulthood. Linear porokeratosis is a harbinger of disseminated porokeratosis that develops 30 or 40 years later. ̶ Cases of superimposed linear Darier disease were forerunners of nonsegmental manifestation. ̶ In a case of Hailey-Hailey disease, neonatal mosaic lesions heralded nonsegmental involvement that began 22 years later.