Mayuko Ito

Age-Related Decrease of Meiotic Cohesins in Human Oocytes

Aneuploidy in fetal chromosomes is one of the causes of pregnancy loss and of congenital birth defects. It is known that the frequency of oocyte aneuploidy increases with the human maternal age. Recent data have highlighted the contribution of cohesin complexes in the correct segregation of meiotic chromosomes. In mammalian oocytes, cohesion is established during the fetal stages and meiosis-specific cohesin subunits are not replenished after birth, raising the possibility that the long meiotic arrest of oocytes facilitates a deterioration of cohesion that leads to age-related increases in aneuploidy. We here examined the cohesin levels in dictyate oocytes from different age groups of humans and mice by immunofluorescence analyses of ovarian sections. The meiosis-specific cohesin subunits, REC8 and SMC1B, were found to be decreased in women aged 40 and over compared with those aged around 20 years (P<0.01). Age-related decreases in meiotic cohesins were also evident in mice. Interestingly, SMC1A, the mitotic counterpart of SMC1B, was substantially detectable in human oocytes, but little expressed in mice. Further, the amount of mitotic cohesins of mice slightly increased with age. These results suggest that, mitotic and meiotic cohesins may operate in a coordinated way to maintain cohesions over a sustained period in humans and that age-related decreases in meiotic cohesin subunits impair sister chromatid cohesion leading to increased segregation errors.

Increased levels of soluble corin in pre-eclampsia and fetal growth restriction

Atrial natriuretic peptide is biologically activated by the atrial natriuretic peptide-converting enzyme, corin, and has an important role in regulating blood pressure. We detected elevated serum corin levels in women with pre-eclampsia. Interestingly, the serum corin levels were also found to be elevated in pregnancies with a related disorder, unexplained fetal growth restriction (FGR) without hypertension, suggesting that this phenomenon is not simply a response to maternal hypertension. CORIN mRNA levels were not elevated in placentas from pre-eclampsia or unexplained FGR cases. Likewise, similar signal intensities were found for corin in placental syncytiotrophoblast cells by immunostaining. In contrast, corin signals were higher in maternal decidua cells from pre-eclampsia and unexplained FGR cases. These data suggest that corin may be upregulated in maternal decidua in response to an etiologic pathway that is common to pre-eclampsia and FGR.

Intragenic duplication in the PHKD1 gene in autosomal recessive polycystic kidney disease

BackgroundIn the present study, we report on a couple who underwent prenatal genetic diagnosis for autosomal recessive polycystic kidney disease (ARPKD).Case presentationThis healthy couple had previously had a healthy boy but had experienced two consecutive neonatal deaths due to respiratory distress resulting from pulmonary hypoplasia caused by oligohydramnios. The woman consulted our facility after she realized she was pregnant again. We promptly performed a carrier test for the PKHD1 gene by target exome sequencing of samples from the couple. A pathogenic mutation was identified only in the paternal allele (c.9008C>T, p.S3003F). The mutation was confirmed by Sanger sequencing of the DNA from formalin-fixed, paraffin-embedded, kidney tissue of the second neonate patient and was not found in the healthy sibling. We then performed haplotype analyses using microsatellite markers scattered throughout the PKHD1 gene. DNA from the amniocentesis was determined to belong to a carrier, and the couple decided to continue with the pregnancy, obtaining a healthy newborn. Subsequent detailed examination of the exome data suggested higher read depth at exons 45 and 46. Multiplex ligation-dependent probe amplification allowed identification of duplication of these two exons. This case suggests the potential usefulness of target exome sequencing in the prenatal diagnosis of the PKHD1 gene in ARPKD.ConclusionsThis is the first report of intragenic duplication in the PKHD1 gene in ARPKD.

Preimplantation genetic diagnosis/screening by comprehensive molecular testing

Although embryo screening by preimplantation genetic diagnosis (PGD) has become the standard technique for the treatment of recurrent pregnancy loss in couples with a balanced gross chromosomal rearrangement, the implantation and pregnancy rates of PGD using conventional fluorescence in situ hybridization (FISH) remain suboptimal. Comprehensive molecular testing, such as array comparative genomic hybridization and next-generation sequencing, can improve these rates, but amplification bias in the whole genome amplification method remains an obstacle to accurate diagnosis. Recent advances in amplification procedures combined with improvements in the microarray platform and analytical method have overcome the amplification bias, and the data accuracy of the comprehensive PGD method has reached the level of clinical laboratory testing. Currently, comprehensive PGD is also applied to recurrent pregnancy loss due to recurrent fetal aneuploidy or infertility with recurrent implantation failure, known as preimplantation genetic screening. However, there are still numerous problems to be solved, including misdiagnosis due to somatic mosaicism, cell cycle-related background noise, and difficulty in diagnosis of polyploidy. The technology for comprehensive PGD also requires further improvement.

Twin pregnancy with chromosomal abnormalities mimicking a gestational trophoblastic disorder and coexistent foetus on ultrasound

Akiko Ohwaki, Haruki Nishizawa, Noriko Aida, Takema Kato, Asuka Kambayashi, Jun Miyazaki, Mayuko Ito, Makoto Urano, Yuka Kiriyama, Makoto Kuroda, Masahiro Nakayama, Shin-Ichi Sonta, Kaoru Suzumori, Takao Sekiya, Hiroki Kurahashi and Takuma Fujii Department of Obstetrics and Gynecology, Fujita Health University School of Medicine, Toyoake, Japan; Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Japan; Department of Diagnostic Pathology, Fujita Health University School of Medicine, Toyoake, Japan; Department of Pathology and Laboratory Medicine, Osaka Medical Center and Research Institute for Maternal and Child Health, Izumi, Japan; Fetal Life Science Center, Ltd, Nagoya, Japan

Multiplex PCR in noninvasive prenatal diagnosis for FGFR3-related disorders: Multiplex PCR in NIPT for FGFR3 gene

Thanatophoric dysplasia and achondroplasia are allelic disorders caused by a constitutively active mutation in the FGFR3 gene. Because thanatophoric dysplasia is a lethal disorder and achondroplasia is non‐lethal, they need to be distinguished after ultrasound identification of fetal growth retardation with short limbs. Accordingly, we have developed a noninvasive prenatal test using cell‐free fetal DNA in the maternal circulation to distinguish thanatophoric dysplasia and achondroplasia. A multiplex PCR system encompassing five mutation hotspots in the FGFR3 gene allowed us to efficiently identify the responsible mutation in cell‐free DNA in all examined pregnancies with a suspected thanatophoric dysplasia or achondroplasia fetus. This system will be helpful in the differential diagnosis of thanatophoric dysplasia and achondroplasia in early gestation and in couples concerned about the recurrence of thanatophoric dysplasia due to germinal mosaicism.

Potentially effective method for fetal gender determination by noninvasive prenatal testing for X-linked disease

Examination of maternal plasma cell‐free DNA (cfDNA) for noninvasive prenatal testing for fetal trisomy is a highly effective method for pregnant women at high risk. This can be also applied to fetal gender determination in female carriers of severe X‐linked disease. Polymerase chain reaction (PCR) analysis is a relatively simpler and less expensive method of detecting Y chromosome‐specific repeats (Y‐specific PCR; YSP), but is limited by the risk of false‐negative results. To address this, we have developed a combined strategy incorporating YSP and an estimation of the fetal DNA fraction. Multiplex PCR for 30 single nucleotide polymorphism (SNP) loci selected by high heterozygosity enables the robust detection of the fetal DNA fraction in cfDNA. The cfDNA sample is first subjected to YSP. When the YSP result is positive, the fetus is male and invasive testing for an X‐linked mutation is then required. When the YSP result is negative, the cfDNA sample is analyzed using multiplex PCR. If fetal DNA is then found in the cfDNA, invasive testing is not then required. If the multiplex PCR analysis of cfDNA is negative for fetal DNA, the fetal gender cannot be determined and invasive testing is still required. Our technique provides a potentially effective procedure that can help to avoid unnecessary invasive prenatal testing in some female carriers of severe X‐linked disease.

Potential role for nectin-4 in the pathogenesis of pre-eclampsia: a molecular genetic study

BackgroundNectins are cell adhesion molecules that play a pivotal role in adherens junctions and tight junctions. Our previous study using whole-genome oligonucleotide microarrays revealed that nectin-4 was upregulated in pre-eclamptic placentas. We investigated the role of nectin-4 in the etiology of pre-eclampsia.MethodsWe investigated the expression of nectin-4 using real-time RT–PCR, western blot and immunostaining. Additionally, we performed matrigel invasion assay and cytotoxicity assay using cells overexpressing the nectin-4.ResultsNECTIN4 transcripts were elevated in pre-eclamptic placentas relative to uncomplicated pregnancies. Nectin-4 protein levels in pre-eclamptic placentas were higher on a semi-quantitative western blot. Nectin-4 was localized at the apical cell membrane in syncytiotrophoblast cells and not at the adherens junctions. Nectin-4 was also detected in cytotrophoblasts and a subset of cells in the decidua. Nectin-4 overexpressing trophoblast cells migrated normally in the matrix. However, Natural killer (NK) cells showed a strong cytotoxic effect against nectin-4 overexpressing trophoblast cells. No causative genetic variation was evident in the NECTIN4 gene from a pre-eclamptic placenta.ConclusionsThere are as yet unknown factors that induce nectin-4 overexpression in trophoblast cells that may contribute to abnormal placentation via an aberrant immune response and the onset of a pre-eclamptic pregnancy.