Variable clinical expression of mosaic trisomy 16 in the newborn infant

Mosaic Trisomy 16 Associated with Left Lung Agenesis, Abnormal Left Arm, and Right Pulmonary Artery Stenosis: Expanding the Phenotype and Review of the Literature

Trisomy 16 is the most common autosomal trisomy found in spontaneous abortions with mosaic versions seen in survivors. However, surviving children have multiple congenital defects and are at risk of growth and developmental delay. We report an additional case of mosaic trisomy 16 diagnosed by amniocentesis and confirmed after birth. Our patient is the first documented case of living mosaic trisomy 16 with the malformation constellation of lung agenesis, left pulmonary artery agenesis, congenital heart defects, and ipsilateral radial ray and limb abnormalities, expanding the phenotype of this rare condition. Additionally, this individual's unique combination of lung and cardiac defects caused morbidities that were challenging to manage and complicated family counseling as well.

Partial trisomy 16q21➔qter due to an unbalanced segregation of a maternally inherited balanced translocation 46,XX,t(15;16)(p13;q21): a case report and review of literature

Background

Partial trisomy is often the result of an unbalanced segregation of a parental balanced translocation. Partial trisomy16q is characterized by a common, yet non-specific group of craniofacial dysmorphic features, and systemic malformations with limited post-natal survival. Most of the cases of partial trisomy 16q described in the scientific literature have reported only one, or less frequently two cardiac defects in the affected babies. Herein, we report a case of partial trisomy 16q21➔qter with multiple and complex cardiac defects that have not previously been reported in association with this condition.

Case presentation

We report the phenotypic and cytogenetic features of a Sri Lankan female infant with partial trisomy 16q21➔qter. The baby had a triangular face with downslanting eyes, low set ears and a cleft palate. Systemic abnormalities included multiple cardiac defects, namely double outlet right ventricle, ostium secundum atrial septal defect, mild pulmonary stenosis, small patent ductus arteriosus, and bilateral superior vena cavae. An anteriorly placed anus was also observed. The proband was trisomic for 16q21➔qter chromosomal region with a karyotype, 46,XX,der(15)t(15;16)(p13;q21)mat. The chromosomal anomaly was the result of an unbalanced segregation of a maternal balanced translocation; 46,XX,t(15;16)(p13;q21). Partial trisomy 16q was established by fluorescence in-situ hybridization analysis.

Conclusions

The craniofacial dysmorphic features and the presence of cardiac and anorectal malformation in the proband are consistent with the phenotypic spectrum of partial trisomy 16q reported in the scientific literature. More proximal breakpoints in chromosome 16q are known to be associated with multiple cardiac abnormalities and poor long-term survival of affected cases. This report presents a unique case with multiple, complex cardiac defects that have not previously been described in association with a distal breakpoint in 16q. These findings have important diagnostic and prognostic implications.

Mosaic trisomy 16: what are the obstetric and long-term childhood outcomes?

PURPOSE

To evaluate obstetric and neonatal outcomes as well as long-term neurodevelopmental outcomes and quality of life among prenatally detected cases of mosaic trisomy (MT16) and confined placental mosaicism (CPM) for trisomy 16.

METHODS

We recruited participants for this cross-sectional study through an international registry of families with children diagnosed with MT16 or CPM. Parents were interviewed about expectations based on prenatal counseling as well as about actual perinatal outcomes, congenital anomalies, medical conditions, and school progress. Health-related quality of life (HRQOL) was assessed via the Pediatric Quality of Life Inventory 4.0 Generic Core Scales.

RESULTS

Forty-four families were enrolled, and 68.2% of the children were female. Common complications were gestational hypertension (gHTN) or preeclampsia (38.1%), preterm delivery (PTD; 71.4%), cesarean delivery (CD; 73.8%), birth weight <10th percentile (73.8%), neonatal intensive care unit (NICU) admission (88.1%), and congenital anomalies (59.5%). However, 81.8% of school-aged children were entirely in mainstream classes, and median physical, psychosocial, and total HRQOL scores were high: 90.6 (34.4-100), 86.7 (35-100), and 84.8 (34.8-100), respectively (100 = optimal quality of life).

CONCLUSION

Several obstetric and neonatal complications are common with pregnancies affected by MT16 or CPM. However, the majority of children demonstrate normal neurodevelopmental outcomes and high HRQOL.Genet Med advance online publication 06 April 2017.

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.

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.

Prenatal findings in trisomy 16q of paternal origin

A 34-year-old pregnant woman was referred at 30 weeks of gestation with suspected fetal congenital heart disease. On prenatal ultrasound the following anomalies were detected: intra-uterine growth retardation, micrognathia, coarctation of the aorta with ventricular and atrial septal defects, ambiguous external genitalia, and clinodactyly of one hand with adducted thumb. Prenatal karyotyping was offered but refused by the patient. The fetus was delivered by Caesarean section due to fetal distress at 36 weeks of gestation. The neonate, weighing 2150 g was transferred to the neonatal intensive care unit, where he died 10 days later. The karyotype from peripheral blood lymphocytes was 46,XY+der(20)t(16;20)(q12.1;p13)pat. The maternal karyotype was unremarkable, whereas the father had the translocation t(16;20)(q12.1;p13). Necropsy confirmed all the prenatal findings. These are discussed together with the implications of the chromosomal diagnosis and the pertinent literature is reviewed.

Mosaic trisomy 16 ascertained through amniocentesis: evaluation of 11 new cases

Trisomy 16, once thought to result uniformly in early pregnancy loss, has been detected in chorionic villus samples (CVS) from on-going pregnancies and was initially ascribed to a second, nonviable pregnancy. Prenatally detected trisomy 16 in CVS and its resolution to disomy has led to the reexamination of the viability of trisomy 16. This study evaluates 11 cases of mosaic trisomy 16 detected through second trimester amniocentesis. In 9 of the 11 cases, amniocenteses were performed in women under the age of 35 because of abnormal levels of maternal serum alpha-fetoprotein (MSAFP) or maternal serum human chorionic gonadotropin (MShCG). The other two amniocenteses were performed for advanced maternal age. Five of the 11 pregnancies resulted in liveborn infants, and six pregnancies were electively terminated. The liveborn infants all had some combination of intrauterine growth retardation (IUGR), congenital heart defects (CHD), or minor anomalies. Two of them died neonatally because of complications of severe congenital heart defects. The three surviving children have variable growth retardation, developmental delay, congenital anomalies, and/or minor anomalies. In the terminated pregnancies, the four fetuses evaluated by ultrasound or autopsy demonstrated various congenital anomalies and/or IUGR. Cytogenetic and fluorescent in situ hybridization studies identified true mosaicism in 5 of 10 cases examined, although the abnormal cell line was never seen in more than 1% of cultured lymphocytes. Placental mosaicism was seen in all placentas examined and was associated with IUGR in four of seven cases. Maternal uniparental disomy was identified in three cases. Mosaic trisomy 16 detected through amniocentesis is not a benign finding but associated with a high risk of abnormal outcome, most commonly IUGR, CHD, developmental delay, and minor anomalies. The various outcomes may reflect the diversity of mechanisms involved in the resolution of this abnormality. As 80% of these patients were ascertained because of the presence of abnormal levels of MSAFP or MShCG, the increased use of maternal serum screening should bring more such cases to clinical attention.

Severe fetal malformations associated with trisomy 16 confined to the placenta

Chorionic villus sampling (CVS) and amniocentesis were performed on a pregnant woman during her 24th week of amenorrhoea following an ultrasound scan which showed a fetus with hydrocephaly, intrauterine growth retardation (IUGR), and a single umbilical artery. The direct karyotype from the cytotrophoblast was non-mosaic 47,XXX,+16, while in amniotic fluid and several fetal tissues, studied post-mortem, a normal 46,XX karyotype was found in more than 400 cells. Uniparental disomy (UPD) was excluded by molecular genetic studies. Autopsy confirmed the echographic findings; in addition, agenesis of the corpus callosum and polysplenia were observed. This is the second example of congenital abnormality associated with confined placental mosaicism (CPM) for trisomy 16, without evidence of either UPD or an apparent contribution of abnormal cells to the fetus.

Prenatal diagnosis of an infant with mosaic trisomy 16 of paternal origin

We present the first case of an infant with paternally-derived mosaic trisomy 16. Amniocentesis following an elevated maternal serum alpha-fetoprotein level and early fetal growth restriction at 19 weeks detected a high level of mosaicism with 25/33 colonies demonstrating trisomy 16 and 8/33 colonies with a normal 46,XX karyotype. Molecular studies revealed a paternal origin of the trisomy which was present in amniotic fluid cells, representing either a post-zygotic error or a meiosis II non-disjunction without crossing-over. In addition, there was normal biparental inheritance in the normal cell line. The symmetrically growth-restricted fetus was closely monitored for the remainder of the gestation. Decreased fetal movements at 36 weeks in conjunction with electronic fetal monitoring showing evidence of fetal distress necessitated abdominal delivery. Severe growth restriction, mild facial dysmorphism, and cardiac anomalies were identified. Microsatellite analysis demonstrated biparental inheritance in skin fibroblasts with a paternal origin for the trisomy in the placenta. Follow-up cytogenetic studies of additional tissues revealed 85 per cent trisomy 16 mosaicism in the placenta, yet only cytogenetically normal cells in lymphocytes and fibroblasts.

Trisomy 16 mosaicism in amniotic fluid cell cultures

Trisomy 16 mosaicism was found in amniotic fluid cells in a patient undergoing amniocentesis because of elevated second-trimester maternal serum alpha-fetoprotein (MSAFP) (2.80 MOM), a markedly elevated human chorionic gonadotropin level (hCG) (12.02 MOM), and a Down syndrome risk of 1:55. Ultrasound evaluation of the fetus indicated the presence of an atrial septal defect and clinodactyly. Cytogenetic analyses of various fetal tissues using fluorescence in situ hybridization (FISH) failed to detect substantial numbers of trisomy 16 cells; however, trisomy 16 mosaicism was identified in placental tissue. Molecular genetic analysis at five different loci [four analysed by polymerase chain reaction (PCR) and one by Southern blot analysis] failed to show any evidence for uniparental disomy. Although trisomy 16 cells could not be clearly demonstrated in the fetus, the presence of a clinically significant proportion of aneuploid cells early in development could not be excluded and it therefore cannot be assumed that a 'confined placental mosaicism' existed. The markedly elevated hCG and elevated MSAFP levels are consistent with abnormal placental function in trisomy 16 mosaicism. Serial ultrasound evaluation (to detect any late-onset growth retardation) and fetal echocardiography may be indicated for patients with extraordinarily high levels of hCG, especially if MSAFP is also elevated.

Uniparental disomy and genome imprinting: an overview

The following paper is concerned with potential changes in the normal epigenetic process in a diploid individual, when a chromosome pair or segment is inherited from one parent only, instead of the expected biparental contribution. This aberrant mode of transmission arises from the high rate of gamete aneuploidy in humans. It has received the name uniparental disomy (UPD), and has emerged as an important factor in the new field of nontraditional inheritance, depicted in Table 1.

The following definitions may foster a better understanding of this discussion.

UPDis the inheritance ofbothcopies of a chromosome [or chromosomal segment(s)] from asingleparent, instead of the normal biparental transmission of the pair. Inisodisomy,the two uniparental copies areidentical, being derived from the same parental chromosome. Inheterodisomy, the two uniparental chromosomes aredifferent, being derived from the homologues of a pair.

Trisomy 16 fetus surviving into the second trimester

A 27-year-old gravida 4, para 3 was found to have anhydramnios at 14 weeks' gestation following a size/date discrepancy noted at her routine prenatal visit. A detailed ultrasound revealed multiple fetal anomalies including congenital heart defect, chest hypoplasia, and bilateral dysplastic kidneys. Karyotype revealed trisomy 16 in 15/15 cells from a tissue specimen obtained from the fetal cord insertion site following elective pregnancy termination.

Uniparental isodisomy for chromosome 16 in a growth-retarded infant with congenital heart disease

We report a growth-retarded infant with congenital heart disease and maternal isodisomy for chromosome 16. Non-mosaic trisomy 16 was detected at mid-trimester chorionic villus sampling, performed because biochemical screening indicated an increased Down's syndrome risk. Further karyotyping analysis of the placenta, after delivery, showed a 50 per cent mosaic trisomy 16. The infant had an atrioventricular (A-V) canal defect, scoliosis, and several minor dysmorphic features. Although uniparental disomy for chromosome 16 has been reported previously, to our knowledge this is the first case of uniparental isodisomy for chromosome 16 which has been investigated with multiple DNA probes.

Postnatal confirmation of prenatally diagnosed trisomy 16 mosaicism in two phenotypically abnormal liveborns

Two phenotypically abnormal liveborns in whom trisomy 16 mosaicism was diagnosed prenatally by amniocentesis are described. Analysis of a percutaneous umbilical blood sample in one case revealed a normal chromosomal complement. Ultrasound examinations performed at the time of amniocentesis were normal. Serial sonography during the late second and third trimesters demonstrated progressive intrauterine growth retardation (IUGR) in both fetuses and a cardiac defect in one. At birth, both infants had dysmorphic features and multiple congenital anomalies. Trisomy 16 mosaicism was confirmed postnatally in both infants in skin fibroblasts; however, peripheral blood samples contained only chromosomally normal cells. The two mosaic trisomy 16 cases described in this report, together with the five confirmed cases reported previously, demonstrate the need for caution in the counselling of patients when trisomy 16 mosaicism is diagnosed prenatally in amniotic fluid samples. Such cases potentially can result in the birth of dysmorphic infants with significant birth defects, growth retardation, and possible developmental disabilities.