Novel Nonsense Mutation in the NLRP7 Gene Associated with Recurrent Hydatidiform Mole

AIM

This study aimed to clarify the genetic and epigenetic features of recurrent hydatidiform mole (RHM) in Japanese patients.

METHODS

Four Japanese isolated RHM cases were analyzed using whole-exome sequencing. Villi from RHMs were collected by laser microdissection for genotyping and DNA methylation assay of differentially methylated regions (DMRs). Single nucleotide polymorphisms of PEG3 and H19 DMRs were used to confirm the parental origin of the variants.

RESULTS

A novel homozygous nonsense mutation in NLRP7 (c.584G>A; p.W195X) was identified in 1 patient. Genotyping of one of her molar tissue revealed that it was biparental but not androgenetic in origin. Despite the fact that the RHM is biparental, maternally methylated DMRs of PEG3, SNRPN and PEG10 showed complete loss of DNA methylation. A paternally methylated DMR of H19 retained normal methylation.

CONCLUSIONS

This is the first Japanese case of RHM with a novel homozygous nonsense NLRP7 mutation and a specific loss of maternal DNA methylation of DMRs. Notably, the mutation was identified in an isolated case of an ethnic background that has not previously been studied in this context. Our data underscore the involvement of NLRP7 in RHM pathophysiology and confirm that DNA methylation of specific regions is critical.

Genome-wide parent-of-origin DNA methylation analysis reveals the intricacies of human imprinting and suggests a germline methylation-independent mechanism of establishment

Differential methylation between the two alleles of a gene has been observed in imprinted regions, where the methylation of one allele occurs on a parent-of-origin basis, the inactive X-chromosome in females, and at those loci whose methylation is driven by genetic variants. We have extensively characterized imprinted methylation in a substantial range of normal human tissues, reciprocal genome-wide uniparental disomies, and hydatidiform moles, using a combination of whole-genome bisulfite sequencing and high-density methylation microarrays. This approach allowed us to define methylation profiles at known imprinted domains at base-pair resolution, as well as to identify 21 novel loci harboring parent-of-origin methylation, 15 of which are restricted to the placenta. We observe that the extent of imprinted differentially methylated regions (DMRs) is extremely similar between tissues, with the exception of the placenta. This extra-embryonic tissue often adopts a different methylation profile compared to somatic tissues. Further, we profiled all imprinted DMRs in sperm and embryonic stem cells derived from parthenogenetically activated oocytes, individual blastomeres, and blastocysts, in order to identify primary DMRs and reveal the extent of reprogramming during preimplantation development. Intriguingly, we find that in contrast to ubiquitous imprints, the majority of placenta-specific imprinted DMRs are unmethylated in sperm and all human embryonic stem cells. Therefore, placental-specific imprinting provides evidence for an inheritable epigenetic state that is independent of DNA methylation and the existence of a novel imprinting mechanism at these loci.

Variable maternal methylation overlapping the nc886/vtRNA2-1 locus is locked between hypermethylated repeats and is frequently altered in cancer

Cancer is as much an epigenetic disease as a genetic one; however, the interplay between these two processes is unclear. Recently, it has been shown that a large proportion of DNA methylation variability can be explained by allele-specific methylation (ASM), either at classical imprinted loci or those regulated by underlying genetic variants. During a recent screen for imprinted differentially methylated regions, we identified the genomic interval overlapping the non-coding nc886 RNA (previously known as vtRNA2-1) as an atypical ASM that shows variable levels of methylation, predominantly on the maternal allele in many tissues. Here we show that the nc886 interval is the first example of a polymorphic imprinted DMR in humans. Further analysis of the region suggests that the interval subjected to ASM is approximately 2 kb in size and somatically acquired. An in depth analysis of this region in primary cancer samples with matching normal adjacent tissue from the Cancer Genome Atlas revealed that aberrant methylation in bladder, breast, colon and lung tumors occurred in approximately 27% of cases. Hypermethylation occurred more frequently than hypomethylation. Using additional normal-tumor paired samples we show that on rare occasions the aberrant methylation profile is due to loss-of-heterozygosity. This work therefore suggests that the nc886 locus is subject to variable allelic methylation that undergoes cancer-associated epigenetic changes in solid tumors.

Enantiodifferentiating Z-E photoisomerization of cyclooctene sensitized by DNA and RNA

DNA and RNA have been shown for the first time to function as chiral photosensitizers in aqueous solution, to effect the enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z), giving the chiral (E)-isomer in enantiomeric excesses (ee's) of up to 15%. In order to elucidate the effect of nucleotide sequence, enantiodifferentiating photoisomerization of 1Z was also performed using oligo and homopolynucleotides as chiral sensitizer. The -18.8% ee was observed by using d(T)15.d(A)15 as sensitizer, whereas sensitization by the poly(U).poly(A) duplex gave only racemic (E)-cyclooctene. From these results, oligothymidine sequence is essential for efficient enantioselective photoisomerization of 1Z.

Serum retinol level and risk of subsequent cervical cancer in cases with cervical dysplasia

We followed up on 134 women who had been diagnosed with cervical dysplasia to examine the relationship of dietary and serum vitamin A to subsequent cervical cancer. The subjects were women attending the Papanicolaou test screening for residents in Miyagi, Japan and histologically diagnosed as having cervical dysplasia between October 1987 and September 1988. Personal interviews were carried out, and blood samples were taken on the date of diagnosis of cervical dysplasia. The subjects were followed-up with cervical smear and colposcopy at about 3-month intervals from the date of interview until the end of February 1995. During the follow-up, 8 women (5.9%) developed cancer in situ or invasive cervical cancer and 106 (79.1%) reverted to normal. The rate of progression of the cancer in situ or invasive cervical cancer was 4.5 times higher in women with lower serum retinol levels than those with higher serum retinol levels (p = 0.08). The results suggest an association of low serum retinol level with development of cervical cancer.

Decreased serum retinol levels in women with cervical dysplasia

To examine the relationship of dietary and serum vitamin A to the risk of cervical dysplasia, a case-control study was conducted in Miyagi, Japan. Cases were 137 women who were found by Papanicolaou test screening and histological examination provided by Miyagi Cancer Society between October 1987 and September 1988 to have cervical dysplasia. Controls were selected from participants of the general health examination provided by the Society and individually matched to cases on age and screening date. The consumption of retinol or carotene-rich foods during the past 7 days was assessed at interview. Information was also collected about other risk factors of cervical dysplasia, such as reproductive histories and sexual behaviour. The mean serum retinol levels were significantly lower among cases compared with controls, although dietary intake levels of retinol and carotene were not different between the two groups. When examined by tertile, the risk of cervical dysplasia was significantly higher among women in the highest tertile of dietary vitamin A level. An inverse association was observed between serum retinol level and risk of cervical dysplasia, although it did not achieve statistical significance.

The evaluation of screening for gastric cancer in Miyagi Prefecture, Japan: a population-based case-control study

Although a screening program for gastric cancer, using barium X-ray examination, has been carried out widely in Japan for the past 3 decades, there is insufficient evidence to confirm its effectiveness in terms of reducing mortality. To evaluate the effectiveness of the screening, a population-based case-control study was carried out in Miyagi Prefecture, Japan. Case subjects, who had died from gastric cancer (198) and control subjects matched in age, sex and residence (577) were selected from among members of the National Health Insurance. Their screening histories during 5 years before the cases were diagnosed were surveyed on the basis of records of the regional cancer registry and the cancer-detection center. The odds ratio (OR) of death from gastric cancer for the persons who participated in the screening at least once during 5 years was 0.41. For those who participated only once during 5 years the OR was 0.43, and for those whose last participation was 5 years earlier it was 0.30. Our data suggest that screening for gastric cancer at 5-year intervals might reduce mortality by 60%, and that the effect might remain for at least 5 years.

An evaluation of mass screening using fecal occult blood test for colorectal cancer in Japan: a case-control study

There is as yet no firm evidence showing that mass screening for colorectal cancer using fecal occult blood tests (FOBTs) reduces the mortality from this cancer. Therefore we evaluated the effectiveness of the screening by a case-control study in Miyagi Prefecture, Japan. The study included as case subjects 28 individuals who had died from colorectal cancer and had had an opportunity to participate in the mass screening before the date of diagnosis as colorectal cancer, and 3 controls for each case subject randomly selected from residents who were alive on the date of death of case subjects and matched by sex, age (within 3 years) and living area using residential files. For each set, i.e., a case subject and 3 controls, screening histories before the date of the diagnosis of the case as colorectal cancer were examined. Both the case subjects and the controls who had participated in the screening at least once within 3 years before the date of diagnosis of the case were classified as "screened." The 28 case subjects consisted of 12 males and 16 females (average age: 60.8 years). The odds ratio of death from colorectal cancer for the screened versus the non-screened persons was 0.24 (95% confidence interval = 0.08-0.76) by the Mantel-Haenszel method. The present study suggests that mass screening using FOBTs for colorectal cancer significantly reduces the mortality from this cancer epidemiologically.

Fukuyama type congenital progressive muscular dystrophy

Clincopathological features of Fukuyama type congenital muscular dystrophy (FCMD), a combination of brain malformation and muscular dystrophy with facial muscle and CNS involvement and high prevalence in Japan, are reviewed. Evidence of progressive dystrophy, negative correlations between muscle enzyme levels and age and CT numbers of muscle and age, are presented. Skeletal muscle histopathology is reviewed. Febrile illness-induced transient exacerbation of muscle weakness is reported. Characteristic brain malformations, e.g. micropolygyria, other dysgenesis, are reviewed. Their severity correlated with maximal mental and motor function. The etiology and significance of low density areas (LDA) in white matter on CT, possibly reflecting delayed or abnormal myelination, and ventricular dilatation are discussed. Spontaneous LDA improvement makes hydrocephaly unlikely. Ophthalmological differential diagnosis from Santavouri disease and Walker-Warburg syndrome, characterized by visual disturbance/glaucoma and microphthalmia/anterior chamber defects, respectively, is discussed. A single defective gene, manifesting as a metabolic error, may produce CNS and ocular defects as well as muscle degeneration in FCMD.