Relationship Between Gene-Phenotype and Clinical Manifestations of Chromosomal Copy Number Variations Indicated by Non-Invasive Prenatal Testing

Objective:To analyze the clinical value of non-invasive prenatal testing(NIPT)in detecting chromosomal copy number variations(CNVs)and to explore the relationship between gene expression and clinical manifestations of chromosomal copy number variations.Methods:3551 naturally conceived singleton pregnant women who underwent NIPT were included in this study.The NIPT revealed abnormalities other than sex chromosome abnormalities and trisomy 13,18,and 21.Pregnant women with chromosome copy number variations underwent genetic counseling and prenatal ultrasound examination.Interventional prenatal diagnosis and chromosome microarray analysis(CMA)were performed.The clinical phenotypes and pregnancy outcomes of different prenatal diagnoses were analyzed.Additionally,a follow-up was conducted by telephone to track fetal development after birth,at six months,and one year post-birth.Results:A total of 53 cases among 3551 cases showed chromosomal copy number variation.Interventional prenatal diagnosis was performed in 36 cases:27 cases were negative and 8 were consistent with the NIPT test results.This indicates that NIPT’s positive predictive value(PPV)in CNVs is 22.22%.Conclusion:NIPT has certain clinical significance in screening chromosome copy number variations and is expected to become a routine screening for chromosomal microdeletions and microduplications.However,further interventional prenatal diagnosis is still needed to identify fetal CNVs.

Two approaches for calculating female fetal DNA fraction in noninvasive prenatal testing based on size analysis of maternal DNA fragments

The concentration of cell-free fetal DNA fragments should be detected before noninvasive prenatal testing(NIPT).The fetal DNA molecules have significant clinical potential in determining the overall performance of NIPT and clinical interpretation.It is important to measure fetal DNA fraction before NIPT.However,there is still little research on how to calculate the concentration of female fetuses.Two estimation approaches were proposed to calculate fetal DNA fraction,including the fragments size-based approach,aneuploid-based approach,which are all approaches based on chromosome segments.Based on high-throughput sequencing data,two approaches to calculate the DNA fraction of male fetuses were tested and obtained the experiment values,which were close to the actual values.The correlation coefficient of fragments size-based approach was 0.9243(P<0.0001)and the aneuploid-based approach reached 0.9339(P<0.0001).We calculated the concentration of female fetuses and obtained remarkable experimental results.We came up with two approaches for calculating the fetal DNA fraction of female fetuses.It provides an important theoretical basis for the detection of female fetal concentration in future clinical diagnosis.

Discrepancy between non-invasive prenatal testing result and fetal karyotype caused by rare confined placental mosaicism: A case report

BACKGROUND Confined placental mosaicism(CPM)is one of the major reasons for discrepancies between the results of non-invasive prenatal testing(NIPT)and fetal karyotype analysis.CASE SUMMARY We encountered a primiparous singleton pregnant woman with a rare CPM consisting of 47,XY,+21;47,XXY;and 46,XY,who obtained a false-positive result on NIPT with a high risk for trisomy 21.Copy-number variation sequencing on amniotic fluid cells,fetal tissue,and placental biopsies showed that the fetal karyotype was 47,XXY,while the placenta was a rare mosaic of 47,XY,+21;47,XXY;and 46,XY.CONCLUSION The patient had a rare CPM consisting of 47,XY,+21;47,XXY;and 46,XY,which caused a discrepancy between the result of NIPT and the actual fetal karyotype.It is important to remember that NIPT is a screening test,not a diagnostic test.Any positive result should be confirmed with invasive testing,and routine ultrasound examination is still necessary after a negative result.

Noninvasive Prenatal Testing for Fetal XXY Aneuploidies Among Pregnancies in Beijing of China

Objective:To evaluate the screening performance of noninvasive prenatal testing(NIPT)based on high-throughput massively parallel sequencing technology for the fetal XXY aneuploidies among pregnancies in Beijing of China.Methods:The study enrolled 26913 consecutive pregnancies,20-50 years old,who attended the Peking Union Medical College Hospital,Beijing,China,for prenatal screening from January 1,2016 to December 31,2019.Cell-free DNA was extracted from maternal peripheral blood to have a high-throughput massively parallel sequencing procedure.Cases with high-risk of fetal XXY were suggested to take invasive prenatal diagnosis(IPD)for confirmation.Maternal DNA sequencing was performed,if necessary,to find other potential factors that may lead to high-risk results of XXY by NIPT.Results:Among a cohort of 26913 pregnant women,34 were high-risk for fetal XXY,among which 30 accepted IPD while 4 declined.In those who accepted IPD,19 cases were confirmed fetal XXY by chromosome karyotyping analysis while 11 were verified as false positive.Among the 19 confirmed fetal XXY cases,14 elected pregnancy termination.For all the 34 high-risk cases,two were verified maternal sex chromosome aneuploidy.The calculated detection rate,positive predictive value,and false-positive rate of NIPT for fetal XXY in this cohort was 100.00%(19/19),63.33%(19/30),and 0.04%(11/26890),respectively.And the percentage of pregnancy termination was 73.68%(14/19).Conclusion:NIPT could be used as a potential method for fetal XXY screening,although the accuracy needs to be improved.As NIPT is not diagnostic,IPD is strongly recommended for those with high-risk results.For cases with discordance between NIPT and fetal karyotyping,maternal DNA sequencing would help to identify the cause of false-positive/false-negative results.

Prenatal Testing or Screening?

Over the past 50 years,the scope and extent of prenatal diagnosis and screening for genetic disorders have improved geometrically.There has been a pendulum like swing from testing to screening back and forth as new technologies emerge.The concurrent developments of cell free fetal DNA analysis of maternal blood has dramatically changed patient’s choices towards screening.However,with the use of array comparative genomic hybridization of fetal DNA that requires diagnostic procedures(Chorionic villus sampling and amniocentesis),much more extensive diagnosis can be obtained.Until noninvasive methods can replicate what can be done with diagnostic procedures there still will be a"price to be paid"for opting for the non-invasive methods.

New mechanism of partial duplication and deletion of chromosome 8:A case report

BACKGROUND During meiosis,the recombination of homologous chromosomes produces some new heritable mutations,which are the basis of biological evolution and diversity.However,when there is pericentric inversion of chromosomes,unbalanced gametes will be formed in the process of germ cell meiosis.CASE SUMMARY A 23-year-old pregnant woman at 25 wk of gestation wanted to terminate her pregnancy due to fetal chromosomal abnormalities.She had no exposure to toxic or hazardous substances before and during pregnancy,no history of medication usage during pregnancy,and she underwent cystectomy of ovarian cysts in 2017.On the second day of the 16th week of gestation,non-invasive prenatal testing showed chromosome 8 copy number variation.Following genetic counseling,her pregnancy was terminated.CONCLUSION Recombinant offspring chromosome is rarely seen when the inversion segment is shorter than one-third of the chromosome length.In terms of the mechanism of chromosome 8 duplication/deletion occurrence,attention should be paid to the production of unbalanced gametes by the pairing of homologous chromosome during meiosis,and the possibility of mitotic recombination exchange as well.

Reproductive management through integration of PGD and MPS-based noninvasive prenatal screening/diagnosis for a family with GJB2-associated hearing impairment

A couple with a proband child of GJB2 （encoding the gap junction protein connexin 26）-associated hearing impairment and a previous pregnancy miscarriage sought for a reproductive solution to bear a healthy child. Our study aimed to develop a cus- tomized preconception-to-neonate care trajectory to fulfill this clinical demand by integrating preimplantation genetic diagno- sis （PGD）, noninvasive prenatal testing （NIPT）, and noninvasive prenatal diagnosis （N1PD） into the strategy. Auditory and ge- netic diagnosis of the proband child was carried out to identify the disease causative mutations. The couple then received in-vitro-fertilization treatment, and eight embryos were obtained for day 5 biopsy. PGD was performed by short-tandem-repeat linkage analysis and Sanger sequencing of GJB2 gene. Transfer of a GJB2c.235delC heterozygous embryo resulted in a sin- gleton pregnancy. At the 13th week of gestation, genomic DNA （gDNA） from the trio family and cell-free DNA （cfDNA） from maternal plasma were obtained for assessment of fetal chromosomal aneuploidy and GJB2 mutations. NIPT and NIPD showed the absence of chromosomal aneuploidy and GJB2-associated disease in the fetus, which was later confirmed by inva- sire procedures and postnatal genetic/auditory diagnosis. This strategy successfully prevented the transmission of hearing im- pairment in the newborn, thus providing a valuable experience in reproductive management of similar cases and potentially other monogenic disorders.

Clinical Performance of Cell-Free Fetal DNA Testing for Fetal Aneuploidies and Subchromosomal Deletions/Duplications in a Cohort of 19,531 Pregnancies

Objective:We aim to assess the clinical performance of cell-free fetal DNA(cffDNA)testing for detecting common fetal aneuploidies as well as subchromosomal deletions/duplications and explore the pregnancy decisions in screen-positive cases.Methods:A cohort of 19,531 pregnant women was offered cffDNA testing for detection of trisomies 21,18,and 13(T21,T18,and T13);sex chromosome aneuploidies(SCAs);and subchromosomal deletions/duplications.Screen-positive cases were confirmed by karyotyping and single-nucleotide polymorphism array analysis.Results:A total of 47 cases failed the test.The overall screen-positive rate of chromosomal abnormalities was 1.07%(208/19,484),including 57 cases with T21,18 cases with T18,7 cases with T13,106 cases with SCAs,and 20 cases of subchromosomal deletions/duplications.Positive predictive values were 91.30%(42/46),38.46%(5/13),33.33%(2/6),41.33%(31/75),and 27.78%(5/18),respectively.There was no significant difference in the screening of fetal chromosomal aneuploidies in the high-risk group compared with the low-risk group(P>0.05).All of the pregnant women who had confirmed fetal T21,T18,or T13 terminated their pregnancies,except for a case of T13 mosaic,whereas 45.16%(14/31)of women with fetal SCAs continued their pregnancies.Furthermore,17 pregnant women with positive screens for T21,T18,or T13 without a subsequent diagnosis chose to terminate their pregnancy,whereas 29 of 31 women with SCAs chose to continue their pregnancies.Conclusions:CffDNA testing exhibited good screening accuracy for T21,T18,and T13 and also contributed to detecting fetal SCAs and subchromosomal deletions/duplications.Pregnant women with fetal 47,XXX or 47,XYY were more willing to terminate their pregnancy than those with fetal 45,X or 47,XXY.

Prenatal Genotyping of Four Common Oculocutaneous Albinism Genes in 51 Chinese Families

Oculocutaneous albinism（OCA） is an autosomal recessive disorder characterized by hypopigmentation in eyes,hair and skin,accompanied with vision loss.Currently,six genes have been identified as causative genes for non-syndromic OCA（OCA-1w4,6,7）,and ten genes for syndromic OCA（HPS-1e9,CHS-1）.Genetic counseling of 51 Chinese OCA families（39 OCA-1 with mutations in the TYR gene,6 OCA-2 with mutations in the OCA2 gene,4 OCA-4 with mutations in the SLC45A2 gene,1 HPS-1（Hermanskye Pudlak syndrome-1） with mutation in the HPS1 gene,and 1 mixed OCA-1 and OCA-4） led us to perform the prenatal genetic testing of OCA using amniotic fluid cells through the implementation of our optimized strategy.In our cohort,eleven previously unidentified alleles（PUAs）（5 in TYR,2 in OCA2,and 4 in SLC45A2） were found.Three missense PUAs（p.C112 R,p.H363 R and p.G379 V of TYR） and one in-frame deletional PUA（p.S222 del of SLC24A5） led to fetuses with OCA when co-inherited with other disease causative alleles.Three PUAs（p.P152 H and p.W272 X of TYR,p.A486 T of SLC24A5） identified in the OCA probands did not co-transmit with known pathological alleles and thus gave rise to unaffected fetuses.Four PUAs（p.Q83 X and p.A658 T of TYR,p.G161 R and p.G366 R of SLC24A5） did not transmit to the unaffected fetuses.In addition,the in vitro transfection assays showed that the p.S192 Y variant of TYR produced less pigment compared to the wild-type allele.A fetus with a digenic carrier of OCA-1 and OCA-4 was unaffected.In combination with functional assays,the family inheritance pattern is useful for the evaluation of pathogenicity of PUAs and genetic counseling of OCA.

Short-DNA Specific Blocker PCR for Efficient and Simple Enrichment of Cell Free Fetal DNAs with Short Lengths

As an inn ate characteristic,DNA length has attracted more and more atte ntion.The length of some import ant biomarkers such as ctDNA(Circulating tumor DNA)and cffDNA(Cell free fetal DNA)is shorter than that of cell-free DNA.Researchers have utilized the differe nee in length to in crease the abunda nee of ctDNA or cffDNA in total cell-free DNA to overcome the difficulties in detecti on due to their low abundance.