Prenatal diagnosis of a trisomy 7/maternal uniparental heterodisomy 7 mosaic fetus

Low-level mosaic trisomy 7 at amniocentesis in a pregnancy associated with cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, perinatal progressive decrease of the trisomy 7 cell line and a favorable fetal outcome

OBJECTIVE

We present low-level mosaic trisomy at amniocentesis in a pregnancy associated with cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, perinatal progressive decrease of the trisomy 7 cell line and a favorable fetal outcome.

CASE REPORT

A 40-year-old, primigravid woman underwent amniocentesis at 16 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 46,XY in cultured amniocytes. Simultaneous array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed the result of arr (7) × 2-3, (X,Y) × 1, consistent with 24% mosaicism for trisomy 7. Polymorphic DNA marker analysis on the DNA extracted from the uncultured amniocytes and parental bloods excluded uniparental disomy (UPD) 7. Prenatal ultrasound findings were normal. She was referred for genetic counseling at 19 weeks of gestation. No repeat amniocentesis was suggested, and continuing the pregnancy was advised. At 22 weeks of gestation, the result of soluble fms-like tyrosine kinase-1 (sFlt-1)/placental growth factor (PlGF) = 6.1 (normal < 38). She did not have preeclampsia. At 39 weeks of gestation, a 3346-g male baby was delivered without any phenotypic abnormality. aCGH analysis on the DNA extracted from cord blood and placenta revealed the result of arr (1-22) × 2, (X,Y) × 1 with no genomic imbalance in all tissues. When follow-up at age three months, the baby was normal in development and phenotype. The peripheral blood had a karyotype of 46,XY, and interphase fluorescence in situ hybridization (FISH) analysis using the bacterial artificial chromosome (BAC) probes of chromosome 7 showed disomy 7 cells in all 102/102 cells.

CONCLUSION

Low-level mosaic trisomy 7 at amniocentesis can be associated with cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, perinatal progressive decrease of the trisomy 7 cell line and a favorable fetal outcome.

Prenatal diagnosis of a trisomy 7 mosaic case: CMA, CNV-seq, karyotyping, interphase FISH, and MS-MLPA, which technique to choose?

OBJECTIVE

This study aims to perform a prenatal genetic diagnosis of a high-risk fetus with trisomy 7 identified by noninvasive prenatal testing (NIPT) and to evaluate the efficacy of different genetic testing techniques for prenatal diagnosis of trisomy mosaicism.

METHODS

For prenatal diagnosis of a pregnant woman with a high risk of trisomy 7 suggested by NIPT, karyotyping and chromosomal microarray analysis (CMA) were performed on an amniotic fluid sample. Low-depth whole-genome copy number variation sequencing (CNV-seq) and fluorescence in situ hybridization (FISH) were used to clarify the results further. In addition, methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) was performed to analyze the possibility of uniparental disomy(UPD).

RESULTS

Amniotic fluid karyotype analysis revealed a 46, XX result. Approximately 20% mosaic trisomy 7 was detected according to the CMA result. About 16% and 4% of mosaicism was detected by CNV-seq and FISH, respectively. MS-MLPA showed no methylation abnormalities. The fetal ultrasound did not show any detectable abnormalities except for mild intrauterine growth retardation seen at 39 weeks of gestation. After receiving genetic counseling, the expectant mother decided to continue the pregnancy, and follow-up within three months of delivery was normal.

CONCLUSION

In high-risk NIPT diagnosis, a combination of cytogenetic and molecular genetic techniques proves fruitful in detecting low-level mosaicism. Furthermore, the exclusion of UPD on chromosome 7 remains crucial when NIPT indicates a positive prenatal diagnosis of trisomy 7.

Genetic counseling of non-invasive prenatal testing (NIPT) trisomy 7-positive pregnancies

Trisomy 7 is the most common observed type of rare autosomal trisomies (RATs) detected at expanded genome-wide non-invasive prenatal testing (NIPT). Genetic counseling of NIPT trisomy 7-positive pregnancies remains to be not easy because the parents may worry about the likelihood of adverse pregnancy outcomes, fetal abnormality and the necessity of invasive procedures for confirmation of fetal mosaic trisomy 7 and uniparental disomy (UPD) 7. This review provides a comprehensive information on the update issues concerning genetic counseling of NIPT trisomy 7-positive pregnancies.

Clinical manifestations and the prenatal diagnosis of trisomy 7 mosaicism: Two case reports

BACKGROUND

The clinical manifestations of trisomy 7 mosaicism are diverse and nonspecific, so prenatal diagnosis is very difficult.

CASE SUMMARY

Two pregnant women with abnormal prenatal screening results were included. One was a 22-year-old woman (G1P0). At 31st week of gestation, ultrasound revealed that the posterior horn of the left lateral ventricle was 10 mm and the right renal pelvis had a separation of 7 mm. The other pregnant woman was 33 years old (G2P1L1A0), and her fetus was found to have a cardiac malformation at the 24th week of gestation. Copy number variation sequencing, whole-exome sequencing and karyotype analysis were carried out after amniocentesis, and both fetuses were diagnosed with trisomy 7 mosaicism. After parental counseling, one woman continued the pregnancy, and the other woman terminated the pregnancy.

CONCLUSION

In trisomy 7 mosaicism, the low proportion of trisomy does not lead to abortion, but can result in abnormal fetal development, which can be detected via ultrasound. Therefore, clinicians need to pay more attention to various aspects of fetal growth and development, combining with imaging, cellular, molecular genetics and other methods to perform comprehensive evaluations of fetuses to provide more reliable genetic counseling for pregnant women.

Performance of noninvasive prenatal testing for twin pregnancies in South China

OBJECTIVE

The purpose of this study was to evaluate the performance of noninvasive prenatal testing (NIPT) for the detection of chromosomal aneuploidies and copy number variations (CNVs) in twin pregnancies.

METHOD

A cohort of 2010 women with twin pregnancies was recruited. 1331 patients opted for NIPT, and 679 patients opted for expanded NIPT (NIPT-plus). All high-risk patients were advised to undergo invasive prenatal diagnosis. All participants were followed up until 6 months after birth.

RESULTS

Twenty-two cases were predicted to have a high risk of chromosome abnormalities by NIPT, of which 14 pregnant women underwent invasive prenatal diagnosis. The 14 cases included 3 cases of trisomy 21, 1 case of trisomy 18, 1 case of trisomy 7, 2 cases of sex chromosome aneuploidies (SCAs), and 7 cases of CNVs, of which the confirmed cases numbered 2, 1, 0, 1, and 0, respectively. Twenty cases were predicted to have a high risk of chromosome abnormalities by NIPT-plus, of which 16 pregnant women underwent invasive prenatal diagnosis. The 16 cases included 1 case of trisomy 21, 1 case of trisomy 7, 7 cases of SCAs, and 7 cases of CNVs, of which were confirmed in 1, 0, 3, and 2, respectively. No false-negative result was reported during the follow-up period.

CONCLUSION

The NIPT/NIPT-plus has excellent performance in the detection of chromosome aneuploidies in twin pregnancies. But for CNVs, the effectiveness of NIPT is poor, and the NIPT-plus have a certain detection efficiency. It is worth noting that pre- and post-genetic counseling is especially important, and the chorionicity, mode of conception, clinical indications, and fetal fraction should be considered as influencing factors.

Prenatal diagnosis of mosaicism for double aneuploidy of 47,XXY and trisomy 7 (48,XXY,+7) at amniocentesis in a pregnancy with a favorable outcome

OBJECTIVE

We present prenatal diagnosis of mosaicism for double aneuploidy of 47, XXY and trisomy 7 (48,XXY,+7) at amniocentesis in a pregnancy with a favorable outcome.

CASE REPORT

A 33-year-old woman underwent amniocentesis at 17 weeks of gestation because of an increased risk for Down syndrome in maternal serum screening. Amniocentesis revealed a karyotype of 48,XXY,+7[8]/46,XY[16]. Simultaneous array comparative genomic hybridization (aCGH) analysis on uncultured amniocytes revealed the result of arr [GRCh37] (7) × 3 [0.54], (X) × 2 [0.52], (Y) × 1, compatible with trisomy 7 mosaicism and Klinefelter syndrome mosaicism. The parental karyotypes and prenatal ultrasound findings were normal. Repeat amniocentesis performed at 23 weeks of gestation revealed a karyotype of 48,XXY,+7[13]/46,XY[7]. Simultaneous molecular cytogenetic analyses on uncultured amniocytes revealed 30% mosaicism for 48,XXY,+7 by aCGH and 37% (37/100 cells) mosaicism for trisomy 7 and disomy X by interphase fluorescence in situ hybridization (FISH) analysis. Polymorphic DNA marker analysis excluded uniparental disomy (UPD) 7 and indicated a maternal origin of the chromosome aberration. The pregnancy was continued to 39 weeks of gestation, and a 3070-g healthy male baby was delivered. The cord blood had a karyotype of 46,XY, the umbilical cord had a karyotype of 48,XXY,+7[3]/46,XY[37], and the placenta had a karyotype of 48,XXY,+7. At age one month, the neonate was phenotypically normal, and interphase FISH analysis revealed 4.8% (5/105 cells) mosaicism on buccal mucosal cells and 8.9% (8/90 cells) mosaicism on urinary cells for trisomy 7 and disomy X, compared with 2% in normal control. Interphase FISH analysis on buccal mucosal cells at age two months revealed normal findings in 100/100 cells.

CONCLUSION

Mosaic 48,XXY,+7 at amniocentesis without UPD 7 can be associated with a favorable fetal outcome. Cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes may occur in mosaic 48,XXY,+7 at amniocentesis.

The significance of trisomy 7 mosaicism in noninvasive prenatal screening

Background

This study was an evaluation of the role of noninvasive prenatal testing (NIPT) in the detection of trisomy 7 in prenatal diagnosis.

Method

A total of 35 consecutive cases underwent screening for trisomies by cell-free DNA testing between April 2015 and November 2017 due to suspicious NIPT results; these cases represented 0.11% of patients (35/31,250) with similar frequencies of abnormal results among the laboratories performing the tests. NIPT was offered to further screen for common fetal chromosomal abnormalities. Karyotype analysis, chromosomal microarray analysis (CMA), and next-generation sequencing (NGS) were used to detect 20, 14, and 25 patients, respectively, who accepted confirmatory diagnostic testing.

Results

High-risk results by NIPT were recorded for trisomy 7 alone in 29 women: dual aneuploidy in 4 patients and multiple aneuploidy in 2 patients. Karyotype analysis of amniotic fluid cells was normal in all 20 pregnancies, suggesting a probability of confined placental mosaicism. Further CMA data were obtained in 14 of the cases mentioned above, and 2 fetuses were detected with positive results with copy number variation. The NGS results suggested that all these samples were placental chimerisms of chromosome 7, except for one sample that was found to be an additional chimerism of chromosome 2, which was also consistent with the NIPT result.

Conclusion

Our results may be useful for the counseling of pregnant women in the detection of trisomy 7 by NIPT.

Mosaic UPD(7q)mat in a patient with silver Russell syndrome

BACKGROUND

Silver-Russell syndrome (SRS) is one of the imprinting disorders characterized by prenatal and postnatal growth restriction, relative macrocephaly, body asymmetry and characteristic facial features. ~ 10% of SRS cases are known to be associated with maternal uniparental disomy of chromosome 7 (UPD(7)mat). Mosaic maternal segmental UPD of 7q (UPD(7q)mat) is very rare, had only been described in one case before.

CASE PRESENTATION

We reported a second case of mosaic segmental UPD involving 7q. The patient presented with dysmorphic features including thin and short stature, triangular face, moderate protruding forehead, relative macrocephaly, fifth toe clinodactyly and irregular teeth, meeting the clinical diagnosed criteria of SRS. This case indicated that ~ 80% of mosaic UPD(7q)mat lead to the manifestation of main phenotypes of Silver-Russell syndrome.

CONCLUSIONS

Our case support the notion that there are genes control postnatal growth on long arm of chromosome 7 and indicate that ~ 80% of UPD(7q)mat mosaicism level was contributed to the SRS phenotype.

Neonatal Silver-Russell syndrome with maternal uniparental heterodisomy, trisomy 7 mosaicism, and dysplasia of the cerebellum

OBJECTIVES

We report here the unusual association of Silver-Russell syndrome (SRS) and cerebellar dysplasia with trisomy 7 mosaicism and maternal uniparental disomy of chromosome 7 [UPD(7)m].

METHODS

Low-level trisomy 7 mosaicism was diagnosed prenatally on amniocytes, and UPD(7)m was confirmed after birth.

RESULTS

Medical examination at birth showed dysmorphic facial features of SRS. Cytogenetic analysis on several tissues and cells confirmed mosaic trisomy 7. Unusual severe psychomotor retardation, hypotonia, and choreoathetoid movement were noted at 6 months. Brain magnetic resonance imaging showed both cerebellar hypoplasia and dysplasia.

CONCLUSIONS

This unusual association of SRS and dysplasia of the cerebellum might be related to the presence of the trisomy 7 mosaicism on the cerebellum. Our observation strengthens the hypothesis that the phenotype observed in patients with SRS with UPD(7)m might also result from an undetected low level of trisomy 7 mosaicism that could best be revealed by performing cytogenetic investigations.

Maternal uniparental disomy 7 and Silver-Russell syndrome - clinical update and comparison with other subgroups

Maternal uniparental disomy (UPD) 7 is found in approximately 5% of patients with Silver-Russell syndrome. By a descriptive and comparative clinical analysis of all published cases (more than 60 to date) their phenotype is updated and compared with the clinical findings in patients with Sliver-Russell syndrome (SRS) of either unexplained etiology or epimutations of the imprinting center region 1 (ICR1) on 11p15. The higher frequency of relative macrocephaly and high forehead/frontal bossing makes the face of patients with epimutations of the ICR1 on 11p15 more distinctive than the face of cases with SRS of unexplained etiology or maternal UPD 7. Because of the distinct micrognathia in the latter, their triangular facial gestalt is more pronounced than in the other groups. However, solely by clinical findings patients with maternal UPD 7 cannot be discriminated unambiguously from patients with epimutations of the ICR1 on 11p15 or SRS of unexplained etiology. Therefore, both loss of methylation of the ICR1 on 11p15 and maternal UPD 7 should be investigated for if SRS is suspected.

Trisomy 7 mosaicism, maternal uniparental heterodisomy 7 and Hirschsprung's disease in a child with Silver–Russell syndrome

Prenatal trisomy 7 is usually a cell culture artifact in amniocytes with normal diploid karyotype at birth and normal fetal outcome. In the same way, true prenatal trisomy 7 mosaicism usually results in a normal child except when trisomic cells persist after birth or when trisomy rescue leads to maternal uniparental disomy, which is responsible for 5.5-7% of patients with Silver-Russell syndrome (SRS). We report here on the unusual association of SRS and Hirschsprung's disease (HSCR) in a patient with maternal uniparental heterodisomy 7 and trisomy 7 mosaicism in intestine and skin fibroblasts. HSCR may be fortuitous given its frequency, multifactorial inheritance and genetic heterogeneity. However, the presence of the trisomy 7 mosaicism in intestine as well as in skin fibroblasts suggests that SRS and HSCR might possibly be related. Such an association might result from either an increased dosage of a nonimprinted gene due to trisomy 7 mosaicism in skin fibroblasts (leading to SRS) and in intestine (leading to HSCR), or from an overexpression, through genomic imprinting, of maternally expressed imprinted allele(s) in skin fibroblasts and intestine or from a combination of trisomy 7 mosaicism and genomic imprinting. This report suggests that the SRS phenotype observed in maternal uniparental disomy 7 (mUPD(7)) patients might also result from an undetected low level of trisomy 7 mosaicism. In order to validate this hypothesis, we propose to perform a conventional and molecular cytogenetic analysis in different tissues every time mUPD7 is displayed.

Sex-specific chromosome instability in early human development

The predominance of females segregating chromosome aberrations to their offspring has been explained mostly by selection disadvantage of unbalanced products of spermatogenesis. However, analysis of data from the literature supports the idea that somatic cells of early female embryos are similar to female germ cells in that they are prone to malsegregation. The goal of this study was to compare the sex ratio (male to female ratio) of carriers of presumably mitotic-occurring chromosome abnormalities to identify any sex biases. In examining the literature, we found a female prevalence in cases of mosaicism associated with uniparental disomy (UPD) (26 male individuals/conceptions and 45 female individuals/conceptions, sex ratio is 0.58, significantly different from 1.06 in newborn population, P = 0.0292). This predominance was highest at gestational age <16 week (8 male and 22 female conceptuses, sex ratio is 0.36, significantly different from expected figure of 1.28, P = 0.0025), which diminished at later stages of fetal development indicating potential correction of trisomies predominantly in females. There is a threefold prevalence of 46,XX/45,X mosaics over 46,XY/45,X mosaics in prenatally diagnosed cases, which also suggests a gender-specific postzygotic chromosome loss. The male prevalence in Prader-Willi syndrome with maternal UPD of chromosome 15 also can be explained by sex-specific trisomy correction, with predominant loss of a maternal chromosome causing biparental inheritance and therefore, complete correction of trisomy in females (without UPD). Finally, there is a female predominance in carriers of chromosome rearrangement with pericentromere break (mosaicism for Robertsonian translocation/isochromosome, centric fission, nonacrocentric isochromosome, and whole arm rearrangement), in both prenatal (21 males and 36 females, sex ratio is 0.58, P < 0.0184) and postnatal ill-defined cases (14 males and 35 females, sex ratio is 0.40, P = 0.001). Thus, the findings presented in this paper suggest that, in addition to reduction in male fertility, and to probable selection against abnormal cell line(s), there are two mechanisms that contribute to female preponderance among carriers of mosaicism: sex-specific chromosome loss and sex-specific centromere instability. The data obtained suggest that females may have gonadal mosaicism for aneuploidies and structural rearrangements more often than males. This may lead to the maternal origin bias in offspring with trisomies or structural rearrangements.

Uniparental disomy (UPD) other than 15: Phenotypes and bibliography updated

Uniparental disomy (UPD) describes the inheritance of a pair of chromosomes from only one parent. The concept was introduced in Medical Genetics by Engel (1980); Am J Med Genet 6:137-143. Aside UPD 15, which is the most frequent one, up to now (February 2005) 197 cases with whole chromosome maternal UPD other than 15 (124 X heterodisomy, 59 X isodisomy, and 14 cases without information of the mode of UPD) and 68 cases with whole chromosome paternal UPD other than 15 (13 X heterdisomy, 53 X isodisomy, and 2 cases without information of the mode of UPD) have been reported. In this review we discuss briefly the problems associated with UPD and provide a comprehensive clinical summary with a bibliography for each UPD other than 15 as a guide for genetic counseling.

Pigmentary mosaicism following the lines of Blaschko in a girl with a double aneuploidy mosaicism: (47,XX,+7/45,X)

We report on a 6-year-old girl with linear streaks of apparent hypopigmentation and hyperpigmentation following the Blaschko lines, growth retardation, bupthalmos of the left eye, and mild mental retardation. She had a 45,X karyotype in lymphocytes. In cultured fibroblasts a double aneuploidy mosaicism was detected, consisting of a cell line with trisomy for chromosome 7 and a cell line with monosomy for the X-chromosome and no cell line with a normal karyotype. Cutis tricolor or three levels of pigmentation in different skin areas suggested presence of a third, probably normal cell line. Double aneuploidy mosaicism of a cell line with monosomy X and a cell line with trisomy of an autosome is a rare finding. The combination of monosomy X with trisomy of chromosomes 8, 10, 13, 18, and 21 has been reported, but not the combination with trisomy 7. In the 45,X cell line, microsatellite analysis showed loss of the maternal X-chromosome, and presence of a maternal and paternal chromosome 7. The 47,XX,+7 cell line showed a paternal and a maternal X-chromosome, and a paternal and two identical maternal chromosomes 7. Mechanisms that might explain this double aneuploidy mosaicism are discussed.

Clinical outcome and follow-up of the first reported case of Russell-Silver syndrome with the unique combination of maternal uniparental heterodisomy 7 and mosaic trisomy 7

BACKGROUND

Russell-Silver syndrome (RSS) has been associated with maternal uniparental disomy (UPD) for chromosome 7 although the etiology of the syndrome is still unknown. Cases of RSS associated with maternal UPD7 have involved isodisomies, heterodisomies, and mixed isodisomy with heterodisomy simultaneously. This publication is a follow-up report of the postnatal clinical outcome of the first prenatally suspected case of combined mosaic trisomy 7 with maternal uniparental disomy of chromosome 7 (UPD7).

CASE

The diagnosis of RSS in the proband was suspected prenatally because trisomy 7 mosaicism (47,XX,+7[13]/46,XX[19]) and maternal uniparental heterodisomy 7 were both found in amniotic fluid cells. Cord blood karyotype analysis showed only disomic cells (46,XX[50]), whereas postpartum chorionic villus analysis was completely trisomic for chromosome 7 (47,XX,+7[19]). Postnatally, the diagnosis of RSS was confirmed by physical findings, her trisomy 7 mosaicism was confirmed by cytogenetic analysis of her skin biopsy (47,XX,+7[9]/46,XX[20]) and her UPD7 was confirmed on both peripheral blood and skin biopsy using microsatellite markers. During infancy, the proband experienced growth deficiency, persistent hypoglycemia, and psychomotor developmental delay.

CONCLUSIONS

Trisomic rescue as a life-saving mechanism, with subsequent chromosomal mosaicism in combination with UPD may occur more frequently in RSS than has been reported. Systematic testing of cases suspected prenatally or postnatally would be informative regarding the individual contribution of each factor. Imprinting, loss of heterozygosity for recessive genes, and mosaicism may explain the short stature, asymmetry, and the variable expression of the phenotype. The contribution of these mechanisms to the syndrome should be evaluated in these cases.