Genome analysis of myelodysplastic syndromes among atomic bomb survivors in Nagasaki.

Ionizing radiation is a risk factor for myeloid neoplasms including myelodysplastic syndromes (MDS), and atomic bomb survivors have been shown to have a significantly higher risk of MDS. Our previous analyses demonstrated that MDS among these survivors had a significantly higher frequency of complex karyotypes and structural alterations of chromosomes 3, 8, and 11. However, there was no difference in the median survival time between MDS among survivors compared with those of de novo origin. This suggested that a different pathophysiology may underlie the causative genetic aberrations for those among survivors. In this study, we performed genome analyses of MDS among survivors and found that proximally exposed patients had significantly fewer mutations in genes such as TET2 along the DNA methylation pathways, and they had a significantly higher rate of 11q deletions. Among the genes located in the deleted portion of chromosome 11, alterations of ATM were significantly more frequent in proximally exposed group with mutations identified on the remaining allele in 2 out of 5 cases. TP53, which is frequently mutated in therapy-related myeloid neoplasms, was equally affected between proximally and distally exposed patients. These results suggested that the genetic aberration profiles in MDS among atomic bomb survivors differed from those in therapy-related and de novo origin. Considering the role of ATM in DNA damage response after radiation exposure, further studies are warranted to elucidate how 11q deletion and aberrations of ATM contribute to the pathogenesis of MDS after radiation exposure.

Comprehensive methylation analysis of imprinting-associated differentially methylated regions in colorectal cancer.

BACKGROUND: Imprinted genes are regulated by DNA methylation at imprinting-associated differentially methylated regions (iDMRs). Abnormal expression of imprinted genes is implicated in imprinting disorders and tumors. In colorectal cancer (CRC), methylation and imprinting status of the IGF2/H19 domain have been studied. However, no comprehensive methylation analysis of iDMRs in CRC has been reported. Furthermore, the relationship between iDMR methylation status and other methylation-related issues, such as CpG island methylator phenotype (CIMP) and long interspersed element-1 (LINE-1) methylation, remains unclear. RESULTS: We analyzed the methylation status of 38 iDMRs in 106 CRC patients. We also investigated CIMP, LINE-1 methylation, KRAS and BRAF gene mutations, and loss of imprinting (LOI) of IGF2. We further examined the relationship between these factors and clinicopathological factors. The overall trend in iDMR methylation was towards hypermethylation, and iDMRs could be grouped into three categories: susceptible, resistant, and intermediate-to-aberrant methylation. The susceptible and resistant iDMRs consisted of all types of iDMR (gametic and somatic, maternally and paternally methylated). Hypermethylation of multiple iDMRs (HyMiD)-positive status was statistically associated with CIMP-positive status, but not associated with mutations in the BRAF and KRAS genes. HyMiD-positive status was inversely associated with LINE-1 methylation. Among four iDMRs within the IGF2/H19 domain, IGF2-DMR0 hypomethylation occurred most frequently, but was not associated with IGF2 LOI. Finally, we statistically calculated predictive prognostic scores based on aberrant methylation status of three iDMRs. CONCLUSION: In CRC tissues, some iDMRs were susceptible to hypermethylation independent of the type of iDMR and genomic sequence. Although HyMiD-positive status was associated with CIMP-positive status, this was independent of the BRAF and KRAS pathways, which are responsible for CIMP. Since IGF2-DMR0 hypomethylation and aberrant methylation of other iDMRs within the IGF2/H19 domain were not associated with IGF2 LOI, dysfunction of any of the molecular components related to imprinting regulation may be involved in IGF2 LOI. The prognostic score calculated based on aberrant methylation of three iDMRs has potential clinical applications as a prognostic predictor in patients. Further study is required to understand the biological significance of, and mechanisms behind, aberrant methylation of iDMRs and IGF2 LOI in CRCs.

Detection of de novo single nucleotide variants in offspring of atomic-bomb survivors close to the hypocenter by whole-genome sequencing.

Ionizing radiation released by the atomic bombs at Hiroshima and Nagasaki, Japan, in 1945 caused many long-term illnesses, including increased risks of malignancies such as leukemia and solid tumours. Radiation has demonstrated genetic effects in animal models, leading to concerns over the potential hereditary effects of atomic bomb-related radiation. However, no direct analyses of whole DNA have yet been reported. We therefore investigated de novo variants in offspring of atomic-bomb survivors by whole-genome sequencing (WGS). We collected peripheral blood from three trios, each comprising a father (atomic-bomb survivor with acute radiation symptoms), a non-exposed mother, and their child, none of whom had any past history of haematological disorders. One trio of non-exposed individuals was included as a control. DNA was extracted and the numbers of de novo single nucleotide variants in the children were counted by WGS with sequencing confirmation. Gross structural variants were also analysed. Written informed consent was obtained from all participants prior to the study. There were 62, 81, and 42 de novo single nucleotide variants in the children of atomic-bomb survivors, compared with 48 in the control trio. There were no gross structural variants in any trio. These findings are in accord with previously published results that also showed no significant genetic effects of atomic-bomb radiation on second-generation survivors.

Genome-wide association study of HPV-associated cervical cancer in Japanese women.

One of the important factors influencing the development of uterine cervical cancer is human papillomavirus infection in women. Usually, the infecting papillomavirus is eliminated from individuals; however, some retain the virus and this is believed to lead to the development of uterine cervical cancer. It is possible that virus elimination or persistent infection depends on an individual's genetic background. To identify single nucleotide polymorphisms associated with susceptibility to persistent infection or cervical cancer, a genome-wide association study was performed on 226 cases and 186 controls. Some of the single nucleotide polymorphisms showed a P-value < 10(-5); however, no polymorphisms that were significantly associated with susceptibility to cervical cancer were identified.

Copy number alteration and uniparental disomy analysis categorizes Japanese papillary thyroid carcinomas into distinct groups.

The aim of the present study was to investigate chromosomal aberrations in sporadic Japanese papillary thyroid carcinomas (PTCs), concomitant with the analysis of oncogene mutational status. Twenty-five PTCs (11 with BRAF(V600E), 4 with RET/PTC1, and 10 without mutation in HRAS, KRAS, NRAS, BRAF, RET/PTC1, or RET/PTC3) were analyzed using Genome-Wide Human SNP Array 6.0 which allows us to detect copy number alteration (CNA) and uniparental disomy (UPD), also referred to as copy neutral loss of heterozygosity, in a single experiment. The Japanese PTCs showed relatively stable karyotypes. Seven cases (28%) showed CNA(s), and 6 (24%) showed UPD(s). Interestingly, CNA and UPD were rarely overlapped in the same tumor; the only one advanced case showed both CNA and UPD with a highly complex karyotype. Thirteen (52%) showed neither CNA nor UPD. Regarding CNA, deletions tended to be more frequent than amplifications. The most frequent and recurrent region was the deletion in chromosome 22; however, it was found in only 4 cases (16%). The degree of genomic instability did not depend on the oncogene status. However, in oncogene-positive cases (BRAF(V600E) and RET/PTC1), tumors with CNA/UPD were less frequent (5/15, 33%), whereas tumors with CNA/UPD were more frequent in oncogene-negative cases (7/10, 70%), suggesting that chromosomal aberrations may play a role in the development of PTC, especially in oncogene-negative tumors. These data suggest that Japanese PTCs may be classified into three distinct groups: CNA(+), UPD(+), and no chromosomal aberrations. BRAF(V600E) mutational status did not correlate with any parameters of chromosomal defects.