Apparent confined placental mosaicism of trisomy 16 and multiple fetal anomalies: case report

Novel parent-of-origin-specific differentially methylated loci on chromosome 16

BACKGROUND

Congenital malformations associated with maternal uniparental disomy of chromosome 16, upd(16)mat, resemble those observed in newborns with the lethal developmental lung disease, alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). Interestingly, ACDMPV-causative deletions, involving FOXF1 or its lung-specific upstream enhancer at 16q24.1, arise almost exclusively on the maternally inherited chromosome 16. Given the phenotypic similarities between upd(16)mat and ACDMPV, together with parental allelic bias in ACDMPV, we hypothesized that there may be unknown imprinted loci mapping to chromosome 16 that become functionally unmasked by chromosomal structural variants.

RESULTS

To identify parent-of-origin biased DNA methylation, we performed high-resolution bisulfite sequencing of chromosome 16 on peripheral blood and cultured skin fibroblasts from individuals with maternal or paternal upd(16) as well as lung tissue from patients with ACDMPV-causative 16q24.1 deletions and a normal control. We identified 22 differentially methylated regions (DMRs) with ≥ 5 consecutive CpG methylation sites and varying tissue-specificity, including the known DMRs associated with the established imprinted gene ZNF597 and DMRs supporting maternal methylation of PRR25, thought to be paternally expressed in lymphoblastoid cells. Lastly, we found evidence of paternal methylation on 16q24.1 near LINC01082 mapping to the FOXF1 enhancer.

CONCLUSIONS

Using high-resolution bisulfite sequencing to evaluate DNA methylation across chromosome 16, we found evidence for novel candidate imprinted loci on chromosome 16 that would not be evident in array-based assays and could contribute to the birth defects observed in patients with upd(16)mat or in ACDMPV.

Genetic causes of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a moderately prevalent birth defect that, despite advances in neonatal care, is still a significant cause of infant death, and surviving patients have significant morbidity. The goal of ongoing research to elucidate the genetic causes of CDH is to develop better treatment and ultimately prevention. CDH is a complex developmental defect that is etiologically heterogeneous. This review summarizes the recurrent genetic causes of CDH including aneuploidies, chromosome copy number variants, and single gene mutations. It also discusses strategies for genetic evaluation and genetic counseling in an era of rapidly evolving technologies in clinical genetic diagnostics.

Genome-wide detection of uniparental disomy in a fetus with intrauterine growth restriction using genotyping microarrays

OBJECTIVE

To present the clinical and molecular features of a fetus with confined trisomy 16 mosaicism with maternal uniparental disomy (UPD), using various prenatal diagnostic techniques.

MATERIALS AND METHODS

Chromosomal karyotyping was performed on samples of chorionic villi, amniotic fluid cells, amniotic membrane, umbilical cord, fetal skin, and placenta from a fetus with elevated nuchal translucency. Polymorphic short tandem repeat markers and Affymetrix single nucleotide polymorphism (SNP) mapping chips were used for molecular analyses.

RESULTS

Karyotypes from chorionic villi and amniocytes showed 47,XX,+16 and 46,XX, respectively. Short tandem repeat markers on chromosome 16 suggested maternal UPD for chromosome 16. Affymetrix 10K SNP mapping chips were used to simultaneously confirm the difference in karyotypes between the placenta and amniocytes and to diagnose UPD for chromosome 16. Fetal ultrasonography and magnetic resonance imaging identified severe intrauterine growth restriction (IUGR). Autopsy revealed IUGR, incomplete lobulation of bilateral lungs, and malrotation of the intestines. The karyotypes of umbilical cord, fetal skin and amniotic membrane were 46,XX, and the trisomy 16 karyotype appeared to be confined to the placenta.

CONCLUSION

UPD should be investigated as a possible etiology in all cases of unexplained IUGR. SNP microarrays can be useful for confirming this diagnosis.

Prenatal diagnosis of trisomy 16 mosaicism manifested as pulmonary artery stenosis

Trisomy 16 mosaicism detected at midtrimester amniocentesis is rare and indicative of true fetal mosaicism. We report a case of mosaic trisomy 16 diagnosed by amniocentesis in which the sonographic findings included fetal pulmonary artery stenosis, a single umbilical artery, and early onset fetal growth restriction. The pregnancy was legally terminated. A review of previous reports suggests that abnormalities of outlet tracts are rarely encountered in fetuses with trisomy 16 mosaicism revealed via amniocentesis.

Lack of aneuploidy for chromosomes 15, 16, and 18 in placentas from small-for-gestational-age liveborn infants

OBJECTIVE

The purpose of this study was to investigate the frequency of confined placental mosaicism (CPM) in placentas from liveborn infants.

STUDY DESIGN

A retrospective analysis of 51 placentas from small-for-gestational-age (SGA), live born infants (birthweight below 5th centile), and 45 placentas from normally grown infants at term was performed. Aneuploidy for chromosomes 15, 16, and 18 was analyzed with QF-PCR (polymorphic markers) and FISH (centromeric probes).

RESULTS

No trisomic sample was detected with either method. FISH revealed 1 case of monosomy 16 in the SGA group, which was not confirmed by PCR. On the other hand, PCR analysis showed allelic imbalances, ie, deviation of the 1:1 peak ratio > 20%, in 5 cases (4 in the SGA and 1 in the control group; P = .157).

CONCLUSION

Trisomic CPM in liveborn SGA infants is much less frequent than previously appreciated. The occurrence and eventual biologic significance of the observed allelic imbalances needs to be further investigated.

Diaphragmatic defects and limb deficiencies - taking sides

Diaphragmatic defects and limb deficiencies usually occur as independent anomalies, as a polytopic field defect (in which ipsilateral anomalies might be expected) or as wider pattern of defects, potentially involving disturbance of laterality or the midline (in which bilateral or contralateral defects would occur). Data on cases from previous studies and/or the literature were used to determine whether there is an association between the sides involved in the defects. The 88 adequately described cases identified included 20 with de Lange syndrome, seven with Poland anomaly, four with trisomy 18, 52 with other patterns of multiple malformations and five with diaphragmatic and limb defects alone. Evaluation of the position of the limb (left, right, bilateral) and the diaphragmatic defects (left, right, bilateral) did not show significant association in patterns of sidedness (P = 0.48). In 56% of cases, the limb deficiencies were bilateral. Among the 32 unilateral cases, 19 (59%) were ipsilateral (15 left; 4 right) and 13(41%) were contralateral (P = 0.38). Eleven of the 13 contralateral cases had left sided diaphragmatic defects and right sided limb deficiency; four had de Lange syndrome and nine had other patterns of multiple anomalies. Only cases with Poland anomaly or otherwise isolated defects showed a trend towards ipsilateral defects. Most cases with multiple congenital anomalies, had limbs defects on both the right and left (57%) or both sides of the diaphragm were affected (an additional 10%), indicating a widespread dysmorphogenetic process rather than a more restricted field defect. In other cases, defects were bilateral or, if unilateral, reflected the propensities for diaphragmatic defects to more often involve the left side, and limb defects, the right.

Genetic factors in congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a relatively common birth defect associated with high mortality and morbidity. Although the exact etiology of most cases of CDH remains unknown, there is a growing body of evidence that genetic factors play an important role in the development of CDH. In this review, we examine key findings that are likely to form the basis for future research in this field. Specific topics include a short overview of normal and abnormal diaphragm development, a discussion of syndromic forms of CDH, a detailed review of chromosomal regions recurrently altered in CDH, a description of the retinoid hypothesis of CDH, and evidence of the roles of specific genes in the development of CDH.

Variable outcomes in mosaic trisomy 16: five case reports and literature analysis

OBJECTIVES

To report five cases of mosaic trisomy 16 with variable outcomes in the context of the literature on mosaic trisomy 16. Complications in these cases include preeclampsia, IUGR, fetal anomalies, and death, with no predictable pattern.

METHODS

Observation of five new cases and statistical analysis of 125 reported cases of mosaic trisomy 16 with prenatal detection and outcome data.

RESULTS

(1) IUGR, premature delivery, and/or physical anomalies are observed commonly, even when the trisomy is thought to be confined to the placenta; (2) Level II mosaicism for trisomy 16 in amniotic fluid may reflect a true mosaic state with phenotypic consequences; (3) FISH is more sensitive than traditional cytogenetics in detecting mosaicism in all tissue types examined; (4) hCG levels can be extremely elevated, and MS-AFP levels are often elevated; and (5) Uniparental disomy (UPD) increases the rates of IUGR and physical anomalies in CPM cases.

CONCLUSION

While there is no obvious mosaic trisomy 16 syndrome, IUGR and heart defects commonly occur, even if the mosaicism appears to be confined to the placenta. A completely normal outcome occurs only in about 20% of the cases; however, complications can often be limited to prematurity, small-for-gestational-age infants, and/or minor or surgically reparable birth defects.

Imprinted genes and their role in human fetal growth

Growth is defined as the progressive increase in size and is listed as one of the eight main characteristics of life. In human gestation the most rapid growth phase is from 16 to 32 weeks when first there is both cell number and size increase and then from 32 weeks onwards there is continued size increase (Pollack and Divon, 1992). The mechanism of growth in utero is of fundamental interest to clinicians and scientists because of its implications for neonatal health. Growth is multifactorial in origin with both genetics and environment contributing equally large parts. Despite this complexity analysis of the candidate genes involved is possible using simple tissue biopsies at the relevant stages of development. Of particular interest in understanding fetal growth is the analysis of a group of genes that show a parent-of-origin effect known as genomic imprinting. Imprinted genes are not only found in eutherian (placental) and metatherian (marsupial) mammals but surprisingly also in plants. Nevertheless, their evolution in mammals appears to be linked primarily to placentation. It is thought to result from a potential conflict between the parents in terms of the drive to successfully propagate their own separate genes and the mother's added drive for her survival through the pregnancy to reproduce again. This means that the mother wants to restrict fetal growth and the father to enhance it.

Postnatal follow-up of prenatally diagnosed trisomy 16 mosaicism

OBJECTIVE

To determine the long-term outcome of pregnancies prenatally diagnosed with trisomy 16 and identify variables associated with the outcome.

METHODS

We reviewed all published and our unpublished data from trisomy 16 pregnancies for which outcomes were available for children of greater than 1 year of age.

RESULTS

Nineteen cases were diagnosed with trisomy 16 on chorionic villus sampling (CVS) and 17 cases at amniocentesis. Age at last follow-up ranges from 1 to 13 years. Among the CVS group, four out of five patients, with a birth weight and/or length below -2 SD and postnatal growth information, showed catch-up growth (80%). Among the amniotic fluid (AF) group, the birth weight was available in 13 cases. Eleven of the 13 cases had a birth weight less than -2 SD. In eight cases, the length was also below -2 SD (length data unavailable in one case). Nine out of ten cases (90%) and seven out of eight (87.5%) showed catch-up growth for weight and length, respectively. In terms of development, no cases of CVS mosaicism had global developmental delay. One child had a history of delay in speech development. Among the AF-detected cases, 4/17 cases had global developmental delay. All four children with global developmental delay had more than one major malformation compared to 6 out of 32 children in the group with normal development (p = 0.004). The finding of uniparental disomy (UPD) was not associated with developmental delay.

CONCLUSIONS

The majority of prenatally diagnosed trisomy 16 mosaic cases have a good postnatal outcome. However, the finding of mosaicism on AF and the presence of major congenital anomalies are associated with an increased risk of developmental delay.

Mosaic trisomy 16 in a fetus: the complex relationship between phenotype and genetic mechanisms

OBJECTIVES

This study was undertaken to discuss the workup of trisomy 16 pregnancies.

STUDY DESIGN

This case study reports the prenatal detection and postnatal confirmation of mosaic trisomy 16, associated with uniparental disomy (UPD) 16, in a 34-year-old woman who showed elevated maternal serum alpha-fetoprotein and beta-HCG at a gestational age (GA) of 15.5 weeks.

RESULTS

Amniotic fluid (AF) karyotyping at different GAs revealed various levels of trisomy 16 mosaicism (0 to level III). UPD studies at 21 weeks of gestation revealed maternal heterodisomy 16. Serial fetal ultrasonography showed fetal abnormalities: intrauterine growth restriction (IUGR), dilated digestive tract, and gallbladder agenesis. Postmortem examination confirmed the prenatal findings and revealed additional anomalies, such as hypoplastic cerebellum with abnormal gyration of the vermis.

CONCLUSIONS

Workup following prenatal detection of trisomy 16 mosaicism in chorionic villi must include AF karyotyping and serial ultrasound examination of the fetus in order to approach postnatal developmental prognosis.

Prenatal diagnosis of mosaic trisomy 16 associated with congenital diaphragmatic hernia and elevated maternal serum alpha-fetoprotein and human chorionic gonadotrophin

OBJECTIVES

To present the clinical, cytogenetic, and molecular findings of prenatally diagnosed mosaic trisomy 16.

CASE

A 30-year-old gravida 2, para 1 woman was referred for amniocentesis because of a positive maternal serum screen result with elevated maternal serum alpha-fetoprotein (MSAFP) and maternal serum free beta-human chorionic gonadotrophin (MSfreebeta-hCG). Cytogenetic analysis of amniotic fluid at 21 weeks' gestation revealed mosaicism for trisomy 16, 47,XX,+16[3]/46,XX[15]. Ultrasonography demonstrated right diaphragmatic hernia and agenesis of left umbilical artery. The pregnancy was terminated subsequently. The karyotype of the cord blood was 46,XX. Cytogenetic analyses of the multiple sampled tissue specimens showed a karyotype of 47,XX,+16 in the placenta and 47,XX,+16/46,XX with various levels of trisomy 16 in the umbilical cord and skin. Molecular studies showed that the trisomy 16 in the placenta was likely to have resulted from a maternal meiosis II nondisjunction error. Partial dosage increase of an extra maternal allele was noted in the skin and umbilical cord.

CONCLUSION

Fetuses with mosaic trisomy 16 may be associated with congenital diaphragmatic hernia and elevated MSAFP and MShCG. Fetal blood sampling is of a limited value in confirming mosaic trisomy 16 ascertained through amniocentesis.

Evidence for imprinting on chromosome 16: The effect of uniparental disomy on the outcome of mosaic trisomy 16 pregnancies

Although a number of infants with maternal uniparental disomy of chromosome 16 (upd(16)mat) have been reported, the evidence for imprinting on chromosome 16 is not yet conclusive. To test the hypothesis that upd(16)mat has a distinct phenotype, which would support the existence of imprinted gene(s) on chromosome 16, statistical analysis was performed on a large series (n = 83) of mosaic trisomy 16 cases with molecular determination of uniparental disomy status. The incidence of upd(16)mat was 40%, which is consistent with the expected one third from random chromosome loss during trisomy rescue (P = 0.262). In pairwise comparisons, upd(16)mat was found to be associated with fetal growth restriction (P = 0.029) and with increased risk of major malformation (RR = 1.43; P = 0.053). Regression modeling showed that the effect of upd(16)mat on fetal/neonatal weight and malformation is independent of the degree of trisomy detected in the fetus. Regression modeling to control for the degree of trisomy detected in the placenta was not possible due to limited sample size. We conclude that upd(16)mat is associated with more severe growth restriction, and possibly, with higher risk of malformation. Our hypothesis is that imprinted gene(s) exist on chromosome 16 and that abnormal expression of these gene(s) in upd(16)mat cells during development results in decreased cell proliferation. Although we do not advocate prenatal testing for upd(16), studies on the long-term outcome of upd(16)mat neonates is necessary for counseling purposes.