Trisomy 13 mosaicism in a phenotypically normal child: Description of cytogenetic and clinical findings from early pregnancy beyond 2 years of age

Low-level mosaic trisomy 13 at amniocentesis in a pregnancy associated with a positive NIPT result suspicious of trisomy 13, a CVS result of mosaic trisomy 13, cytogenetic discrepancy in various tissues and a favorable fetal outcome

OBJECTIVE

We present low-level mosaic trisomy 13 at amniocentesis in a pregnancy associated with a positive non-invasive prenatal testing (NIPT) result suspicious of trisomy 13, a chorionic villus sampling (CVS) result of mosaic trisomy 13, cytogenetic discrepancy in various tissues and a favorable fetal outcome.

CASE REPORT

A 29-year-old, gravida 2, para 1, woman underwent amniocentesis at 20 weeks of gestation because of a positive NIPT result (Z-score = 20.9, positive ≥3) suspicious of trisomy 13 at 11 weeks of gestation and a CVS result of mosaic trisomy 13 at 14 weeks of gestation. At 14 weeks of gestation, CVS revealed the multiplex ligation-dependent probe amplification (MLPA) result of rea X,Y (P095) × 1, 13 (P095) × 3, 18,21 (P095) × 2/X,Y (P095) × 1, 13,18,21 (P095) × 2 and a karyotype of 48,XY,+13,+mar [9]/47,XY,+mar[16]. She was referred to the hospital for genetic counseling at 15 weeks of gestation, and cytogenetic analysis of parental blood revealed 47,XY,+mar in the father and 46, XX in the mother. Fluorescence in situ hybridization (FISH) analysis on the paternal blood showed that the extra dicentric marker was derived from chromosome 15 without the locus SNRPN (15q11.2), and the result was 47,XY,+mar.ish dic(15) (D15Z1++, SNRPN-, PML-)[20]. Amniocentesis at 20 weeks of gestation revealed a karyotype of 47,XY,+mar pat (20/20). Simultaneous interphase FISH analysis on uncultured amniocytes revealed 32% (32/100 cells) mosaicism for trisomy 13. Quantitative fluorescence polymerase chain reaction (QF-PCR) analysis using the DNA extracted from the parental bloods and uncultured amniocytes excluded uniparental disomy (UPD) 13. Prenatal ultrasound findings were normal. The woman was advised to continue the pregnancy, and a phenotypically normal 2708-g male baby was delivered at 38 weeks of gestation, The cord blood, umbilical cord and placenta had the karyotypes of 47,XY,+mar pat and did not have UPD 13. When follow-up at age two months, the neonate was phenotypically normal. FISH analysis on buccal mucosal cells detected 5.3% (5/95 cells) mosaicism for trisomy 13, compared with 0% in the normal control.

CONCLUSION

Low-level mosaic trisomy 13 at amniocentesis can be associated with a positive NIPT result suspicious of trisomy 13, a CVS result of mosaic trisomy 13, cytogenetic discrepancy in various tissues and a favorable fetal outcome.

Low-level mosaic trisomy 13 at amniocentesis in a pregnancy associated with a favorable fetal outcome and cytogenetic discrepancy in various tissues

OBJECTIVE

We present low-level mosaic trisomy 13 at amniocentesis in a pregnancy associated with associated with a favorable fetal outcome and cytogenetic discrepancy in various tissues.

CASE REPORT

A 38-year-old, gravida 3, para 0, woman underwent amniocentesis at 19 weeks of gestation because of advanced maternal age. This pregnancy was conceived by in vitro fertilization and embryo transfer. Amniocentesis revealed a karyotype of 47,XX,+13[2]/ 46,XX[20] in co-twin A and a karyotype of 46,XY in co-twin B. In co-twin A, among 22 colonies of cultured amniocytes, two colonies had a karyotype of 47,XX,+13, whereas the rest 20 colonies had the karyotype of 46,XX. Array comparative genomic hybridization (aCGH) analysis on the DNA extracted from cultured amniocytes revealed arr (1-22,X) × 2, Y × 0 and detected no genomic imbalance. Prenatal ultrasound and parental karyotypes were normal. Quantitative fluorescence polymerase chain reaction (QF-PCR) analysis on the DNA extracted from the parental bloods and cultured amniocytes excluded uniparental disomy (UPD) 13. The woman was encouraged to continue the pregnancy. At 37 weeks of gestation, a normal 2410-g female co-twin A and a normal 2360-g male co-twin B were delivered without any phenotypic abnormality. The karyotypes of cord blood, umbilical cord and placenta of co-twin A were 46,XX (40/40 cells), 47,XX,+13 [1]/46,XX[39] and 47,XX,+13[36]/46,XX [4], respectively. QF-PCR analysis on cord blood of co-twin A excluded UPD 13. When follow-up at age 1½ years, the neonate of co-twin A was normal in physical and psychomotor development.

CONCLUSION

Low-level true mosaic trisomy 13 at amniocentesis can be associated with a favorable fetal outcome and cytogenetic discrepancy in various tissues.

Low-level mosaic trisomy 13 at amniocentesis associated with a favorable outcome in a pregnancy

OBJECTIVE

We present low-level mosaic trisomy 13 at amniocentesis associated with a favorable outcome in a pregnancy.

CASE REPORT

A 39-year-old woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 47,XY,+13[8]/46,XY[20]. The woman underwent cord blood sampling at 22 weeks of gestation. Cytogenetic analysis of cord blood revealed a karyotype of 47,XY,+13[2]/46,XY[98]. Array comparative genomic hybridization (aCGH) analysis on the DNA extracted from cord blood revealed 10% gene dosage increase in chromosome 13. Prenatal ultrasound findings were unremarkable. After genetic counseling, the parents decided to continue the pregnancy, and a 2,280-g healthy male baby was delivered at 38 weeks of gestation. The parental karyotypes were normal. The cord blood at birth had a karyotype of 47,XY,+13[1]/46,XY[49]. At age one month, interphase fluorescence in situ hybridization (FISH) analysis revealed no trisomy 13 signals in 100/100 buccal mucosal cells, and trisomy 13 signals in 2/54 (3.7%) urinary cells compared with 0/60 cells in the normal control. The neonate was doing well and presented neither phenotypic abnormalities nor psychomotor disorders at age two months.

CONCLUSION

Low-level true mosaic trisomy 13 at amniocentesis without ultrasound abnormalities can be associated with a favorable outcome.

The molecular origins and pathophysiological consequences of micronuclei: New insights into an age-old problem

Micronuclei (MN), the small nucleus-like bodies separated from the primary nucleus, can exist in cells with numerical and/or structural chromosomal aberrations in apparently normal tissues and more so in tumors in humans. While MN have been observed for over 100 years, they were merely and constantly considered as passive indicators of chromosome instability (CIN) for a long time. Relatively little is known about the molecular origins and biological consequences of MN. Rapid technological advances are helping to close these gaps. Very recent studies provide exciting evidence that MN act as key platform for chromothripsis and a trigger of innate immune response, suggesting that MN could affect cellular functions by both genetic and nongenetic means. These previously unappreciated findings have reawakened widespread interests in MN. In this review, the diverse mechanisms leading to MN generation and the complex fate profiles of MN are discussed, together with the evidence for their contribution to CIN, inflammation, senescence and cell death. Moreover, we put this knowledge together into a speculative perspective on how MN may be responsible for cancer development and how their presence may influence the choice of treatment. We suggest that the heterogeneous responses to MN may function physiological to ensure the arrestment, elimination and immune clearance of damaged cells, but pathologically, may enable the survival and oncogenic transformation of cells bearing CIN. These insights not only underscore the complexity of MN biology, but also raise a host of new questions and provide fertile ground for future research.

Detectable clonal mosaicism in the human genome

Human genetic mosaicism is the presence of two or more cellular populations with distinct genotypes in an individual who developed from a single fertilized ovum. While initially observed across a spectrum of rare genetic disorders, detailed assessment of data from genome-wide association studies now reveal that detectable clonal mosaicism involving large structural alterations (>2 Mb) can also be seen in populations of apparently healthy individuals. The first generation of descriptive studies has generated new interest in understanding the molecular basis of the affected genomic regions, percent of the cellular subpopulation involved, and developmental timing of the underlying mutational event, which could reveal new insights into the initiation, clonal expansion, and phenotypic manifestations of mosaic events. Early evidence indicates detectable clonal mosaicism increases in frequency with age and could preferentially occur in males. The observed pattern of recurrent events affecting specific chromosomal regions indicates some regions are more susceptible to these events, which could reflect inter-individual differences in genomic stability. Moreover, it is also plausible that the presence of large structural events could be associated with cancer risk. The characterization of detectable genetic mosaicism reveals that there could be important dynamic changes in the human genome associated with the aging process, which could be associated with risk for common disorders, such as cancer, cardiovascular disease, diabetes, and neurological disorders.

Mosaic trisomy 13 and a sacral appendage

Mosaic trisomy 13 occurs when there is a percentage of trisomic cells for an entire chromosome 13, while the remaining percentage of cells is euploid. The prevalence of this syndrome ranges from 1 in 10 000 to 1 in 20 000 births. Complete, partial or mosaic forms of this disorder can occur. The phenotype of mosaic trisomy 13 patients varies widely. Patients with mosaic trisomy 13 usually have a longer survival and a less severe phenotype compared to patients with complete trisomy 13. Genetic counselling is difficult due to the wide variation among the clinical manifestations of these patients. There have been 49 cases of mosaic trisomy 13 reported in the literature. We report the case of a patient with mosaic trisomy 13, a sacral appendage and a cleft lip and palate.

Structural genetic variation in the context of somatic mosaicism

Somatic mosaicism is the result of postzygotic de novo mutation occurring in a portion of the cells making up an organism. Structural genetic variation is a very heterogeneous group of changes, in terms of numerous types of aberrations that are included in this category, involvement of many mechanisms behind the generation of structural variants, and because structural variation can encompass genomic regions highly variable in size. Structural variation rapidly evolved as the dominating type of changes behind human genetic diversity, and the importance of this variation in biology and medicine is continuously increasing. In this review, we combine the evidence of structural variation in the context of somatic cells. We discuss the normal and disease-related somatic structural variation. We review the recent advances in the field of monozygotic twins and other models that have been studied for somatic mutations, including other vertebrates. We also discuss chromosomal mosaicism in a few prime examples of disease genes that contributed to understanding of the importance of somatic heterogeneity. We further highlight challenges and opportunities related to this field, including methodological and practical aspects of detection of somatic mosaicism. The literature devoted to interindividual variation versus papers reporting on somatic variation suggests that the latter is understudied and underestimated. It is important to increase our awareness about somatic mosaicism, in particular, related to structural variation. We believe that further research of somatic mosaicism will prove beneficial for better understanding of common sporadic disorders.

Are all cases of low-grade mosaic trisomy 13 in amniotic fluid with no fetal malformation in fact confined placental mosaicism? A case report

We report on a case of true prenatal mosaic trisomy 13 on amniotic fluid associated with a normal phenotype at the age of 6 years. The amniocentesis was performed because of advanced maternal age and was controlled by a second sample. Morphological and cardiac ultrasonography did not reveal any fetal malformations. No trisomic cells were found in the fetal blood and a nuclear magnetic resonance imaging (IRM) of the brain was performed during the third trimester found no abnormality of the brain. Finally, at birth cytogenetic analysis was performed on two placental samples for chromosomal analysis: one in an area where the placenta seemed normal, and the other one in an area with infarcted and hemorrhagic aspect. We found a high rate of trisomic cells in the sample with abnormal aspect. Furthermore, no trisomic cell was observed by fluorescent in situ hybridation (FISH) on the buccal smears of the baby. We concluded to a confined placental mosaicism. The good outcome of the child aged 6 years confirms this diagnosis. So in the aim to predict a good development for the child in case of low rate mosaic trisomy 13 in amniotic fluid, we propose at birth: i) to take several samples from the placenta to confirm placental mosaicism; ii) to label by FISH buccal smears with a LSI 13 probe to prove that the baby is not a carrier of the trisomy.

Prenatal diagnosis and genetic counseling for mosaic trisomy 13

Counseling parents of a fetus with trisomy 13 mosaicism remains difficult because of the phenotypic variability associated with the condition; some patients exhibit the typical phenotype of complete trisomy 13 with neonatal death, while others have few dysmorphic features and prolonged survival. This article provides a comprehensive review of the prenatal diagnosis and genetic counseling for mosaic trisomy 13, including confined placental mosaicism 13, mosaic trisomy 13 diagnosed at amniocentesis, and phylloid hypomelanosis in association with mosaic trisomy 13.

Phenotypic variability in trisomy 13 mosaicism: two new patients and literature review

Trisomy 13 mosaicism occurs when two cell lines, one with a normal complement of chromosomes and the other with an additional chromosome 13, are present in the same individual. We present two children with trisomy 13 mosaicism and summarize the literature in 47 published cases. Our first patient is a 4-year-old male with normal development and dysmorphic features that include right microtia, tall forehead, bulbous nose, and high arched palate. The second patient died at 1 day of life secondary to laryngeal stenosis, a previously undocumented finding in trisomy 13. His other dysmorphic features included micrognathia, cleft soft palate, and an axillary pterygium. Several published case reports of patients with trisomy 13 mosaicism have had the typical phenotype of complete trisomy 13 with death in the neonatal period, while others have had few dysmorphic features and prolonged survival. The most common malformations in all 49 cases included ear anomalies, cleft lip and palate, and various congenital heart defects. Intelligence varied from normal in six patients to significant delays and mental retardation in the remainder of cases. There is no clear correlation between the percentage of trisomic cells and the level of intellectual function. The dysmorphic features seen vary considerably from one patient to the next, often making the clinical diagnosis of trisomy 13 mosaicism difficult. In counseling families, medical professionals should state that trisomy 13 mosaicism may lead to physical abnormalities and poor intellectual outcomes, but that the condition does not do so universally with normal development occurring in some individuals.