Trisomy 18 mosaicism in a woman with normal intelligence, pigmentary dysplasia, and an 18 trisomic daughter

Prenatal diagnosis and molecular genetic analysis of recurrent trisomy 18 of maternal origin in two consecutive pregnancies

OBJECTIVE

We present prenatal diagnosis and molecular genetic analysis of recurrent trisomy 18 of maternal origin in two consecutive pregnancies.

CASE REPORT

A 37-year-old, gravida 3, para 1, woman was referred for genetic counseling because of cystic hygroma on ultrasound at 12 weeks of gestation, a previous pregnancy with a fetus with trisomy 18, and an abnormal first-trimester non-invasive prenatal testing (NIPT) result of Z score of 9.74 (normal: -3.0-3.0) in chromosome 18 suggesting trisomy 18 during this pregnancy. The fetus died at 14 weeks of gestation, and a malformed fetus was terminated at 15 weeks of gestation. Cytogenetic analysis of the placenta revealed a karyotype of 47,XY,+18. Quantitative fluorescent polymerase chain reaction (QF-PCR) assays on the DNA extracted from parental bloods and umbilical cord determined a maternal origin of trisomy 18. One year previously, the woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age of 36 years. Amniocentesis revealed a karyotype of 47,XX,+18. Prenatal ultrasound was unremarkable. The mother had a karyotype of 46,XX, and the father had a karyotype of 46,XY. QF-PCR assays on the DNA extracted from parental bloods and cultured amniocytes determined a maternal origin of trisomy 18. The pregnancy was subsequently terminated.

CONCLUSION

NIPT is useful for rapid prenatal diagnosis of recurrent trisomy 18 under such a circumstance.

Mosaic trisomy 18 at amniocentesis associated with a favorable fetal outcome in a pregnancy

OBJECTIVE

We present prenatal diagnosis of mosaic trisomy 18 by amniocentesis associated with a favorable fetal outcome in a pregnancy.

CASE REPORT

A 42-year-old, gravida 4, para 2, woman underwent amniocentesis at 18 weeks of gestation because advanced maternal age. Amniocentesis revealed a karyotype of 47,XX,+18[6]/46,XX[17]. Simultaneous array comparative genomic hybridization (aCGH) on uncultured amniocytes showed the result of 45% mosaicism for trisomy 18. At 25 weeks of gestation, the woman underwent repeat amniocentesis which revealed a karyotype of 47,XX,+18[10]/46,XX[24]. Simultaneous aCGH on uncultured amniocytes showed the result of arr 18p11.32q23 (148,963-78,012,829) × 2.3 [GRCh (hg19)] with a log₂ ratio of 0.2-0.25 compatible with 30-38% mosaicism for trisomy 18. The parental karyotypes were normal. Prenatal ultrasound was unremarkable. Interphase fluorescence in situ hybridization (FISH) on uncultured amniocytes showed 27% (27/100 cells) mosaicism for trisomy 18. Quantitative fluorescent polymerase chain reaction (QF-PCR) on uncultured amniocytes excluded uniparental disomy (UPD) 18. Non-invasive prenatal testing (NIPT) analysis at 34 weeks of gestation revealed a significant gene dosage increase of chromosome 18 (29.95; normal control: -3.0-3.0). At 39 weeks of gestation, a 2840-g phenotypically normal baby was delivered. The cord blood had a karyotype of 47,XX,+18[8]/46,XX[32]. The placenta was trisomy 18 of maternal origin. The umbilical cord had a karyotype of 47,XX,+18[2]/46,XX[38]. At age 1½ months, the peripheral blood had a karyotype of 47,XX,+18[5]/46,XX[35], and FISH analysis on buccal mucosal cells revealed 2% (2/102 cells) mosaicism for trisomy 18. When follow-up at age seven months, the neonate was phenotypically normal, and the peripheral blood had a karyotype of 47,XX,+18[1]/46,XX[39].

CONCLUSIONS

Mosaic trisomy 18 at amniocentesis without abnormal fetal ultrasound can be associated with a favorable outcome, and the abnormal trisomy 18 cell line may decrease progressively after birth.

Detection of paternal origin of fetal trisomy 18 in a pregnancy conceived by assisted reproductive technology and in vitro fertilization

OBJECTIVE

We present detection of paternal origin of fetal trisomy 18 in a pregnancy conceived by assisted reproductive technology (ART) and in vitro fertilization (IVF).

CASE REPORT

A 39-year-old woman underwent ART and IVF because of primary infertility. The woman was infertile because of myoma and endometriosis. Her husband was 39 years old, and the sperm analysis was normal. The couple was phenotypically normal. This pregnancy was conceived successfully by IVF. She received non-invasive prenatal testing at 11 weeks of gestation, the result showed a high risk for trisomy 18. She underwent chorionic villus sampling at 12 weeks of gestation, and the result was 47,XY,+18 in 24/24 cultured chorionic villi cells. Prenatal ultrasound findings were unremarkable. She underwent amniocentesis at 17 weeks of gestation, and the result was 47,XY,+18 in 20/20 colonies of cultured amniocytes. The pregnancy was subsequently terminated. Postnatal cytogeneic analysis confirmed the prenatal diagnosis. Polymorphic DNA marker analysis on the DNAs extracted from the umbilical cord and parental bloods showed a paternal origin of the extra chromosome 18, indicating a paternal origin of fetal trisomy 18. Cytogenetic analysis of paternal blood revealed a karyotype of 46,XY.

CONCLUSION

Fetal trisomy 18 in pregnancies conceived by ART may be of paternal origin, and determination of paternal origin by polymorphic DNA marker analysis is useful for genetic counseling under such a circumstance.

The trisomy 18 syndrome

The trisomy 18 syndrome, also known as Edwards syndrome, is a common chromosomal disorder due to the presence of an extra chromosome 18, either full, mosaic trisomy, or partial trisomy 18q. The condition is the second most common autosomal trisomy syndrome after trisomy 21. The live born prevalence is estimated as 1/6,000-1/8,000, but the overall prevalence is higher (1/2500-1/2600) due to the high frequency of fetal loss and pregnancy termination after prenatal diagnosis. The prevalence of trisomy 18 rises with the increasing maternal age. The recurrence risk for a family with a child with full trisomy 18 is about 1%. Currently most cases of trisomy 18 are prenatally diagnosed, based on screening by maternal age, maternal serum marker screening, or detection of sonographic abnormalities (e.g., increased nuchal translucency thickness, growth retardation, choroid plexus cyst, overlapping of fingers, and congenital heart defects ). The recognizable syndrome pattern consists of major and minor anomalies, prenatal and postnatal growth deficiency, an increased risk of neonatal and infant mortality, and marked psychomotor and cognitive disability. Typical minor anomalies include characteristic craniofacial features, clenched fist with overriding fingers, small fingernails, underdeveloped thumbs, and short sternum. The presence of major malformations is common, and the most frequent are heart and kidney anomalies. Feeding problems occur consistently and may require enteral nutrition. Despite the well known infant mortality, approximately 50% of babies with trisomy 18 live longer than 1 week and about 5-10% of children beyond the first year. The major causes of death include central apnea, cardiac failure due to cardiac malformations, respiratory insufficiency due to hypoventilation, aspiration, or upper airway obstruction and, likely, the combination of these and other factors (including decisions regarding aggressive care). Upper airway obstruction is likely more common than previously realized and should be investigated when full care is opted by the family and medical team. The complexity and the severity of the clinical presentation at birth and the high neonatal and infant mortality make the perinatal and neonatal management of babies with trisomy 18 particularly challenging, controversial, and unique among multiple congenital anomaly syndromes. Health supervision should be diligent, especially in the first 12 months of life, and can require multiple pediatric and specialist evaluations.

Phenotypic spectrum of mosaic trisomy 18: two new patients, a literature review, and counseling issues

Mosaic trisomy 18 occurs when two different cell lines exist in the same individual; one cell line has two copies of chromosome 18, while the other has three copies. Here we present two new patients with mosaic trisomy 18, summarize 31 reported cases from the literature, and discuss management and counseling themes. Our first patient is an 8(1/2)-year-old female with normal intelligence and no significant dysmorphic features other than short stature and cubitus valgus. The second patient is a 21-month-old male with developmental delay, several dysmorphic features, including a patent ductus arteriosus, and normal growth. In general, the phenotype of individuals with mosaic trisomy 18 varies greatly. Some individuals have the complete trisomy 18, Edwards syndrome phenotype with early death while others are phenotypically completely normal. The latter group is exemplified by four normal appearing adults with mosaic trisomy 18 who were identified only after giving birth to children with complete trisomy 18. Further, a wide range of anomalies have been reported, most at low frequencies, including microcephaly, delayed bone age, brachydactyly, congenital heart defects, developmental delay, short stature, and premature ovarian failure. Intellectual capabilities range from profound mental retardation to above average intelligence. There appears to be no correlation with the percentage of trisomic cells in either fibroblasts or leukocytes and the individual's phenotype or intellectual function. We also discuss a variety of counseling issues including long-term survival, reproductive capacity of individuals with mosaic trisomy 18, and recurrence risks.

Turner phenotype in a girl with a 45,X/46,XX/47,XX,+18 mosaicism

We report a girl with Turner syndrome phenotype, whose karyotype on amniocyte culture was 45,X, while cytogenetic analysis on peripheral blood lymphocytes showed the presence of a mosaic chromosome constitution with three different cell lines: 45,X[5]/46,XX[3]/47,XX,+18 [35]. No signs of trisomy 18 were observed and a follow up during childhood revealed normal psychomotor development. Parental origin and mechanism of formation were studied using high polymorphic microsatellites and Quantitative Fluorescent PCR. The 18-trisomic cells showed one paternal allele and two maternal homozygous alleles at different loci of chromosome 18, suggesting a maternal M-II meiotic or a postzygotic error. A biparental origin of the X-alleles in the trisomic cells were determined, being the paternal allele retained in the 45,X cells. The possible mechanism of formation implying meiotic and/or mitotic errors is discussed.

Two unique patients with trisomy 18 mosaicism and molecular marker studies

We report two unusual patients with trisomy 18 mosaicism presenting with minor anomalies and failure to thrive in the first year of life. Chromosome analysis showed trisomy 18 in 30/30 peripheral blood lymphocytes in both children. Analysis of skin fibroblasts in the first child showed normal female chromosomes in 30/30 cells, and the fibroblast karyotype in the second child showed mosaicism for tetrasomy 18p, trisomy 18, and normal female chromosomes (karyotype 47,XX, +i(18)(p10)[47]/47,XX, +18[9] /46,XX[4]). Trisomy 18 commonly results from nondisjunction at maternal meiosis II (MII). Nondisjunction at maternal MII has also been postulated to be the initial step in the formation of tetrasomy 18p. In our second case, the additional chromosome 18 was the result of maternal nondisjunction at MII, consistent with this hypothesis. In the first case, nondisjunction at maternal meiosis I (MI) was responsible for the extra chromosome 18.

Three cell line mosaicism involving structural and numerical abnormalities of chromosome 18 in a 3.5-year-old girl: 47,XX,+18/47,XX,+del(18)(q22)/46,XX

We report on a 3.5-year-old girl with a mosaic karyotype including full trisomy 18, normal cells and a majority of cells with partial trisomy involving an extra chromosome 18 deleted at band q22. She had cardiac and CNS anomalies, dysmorphic facial features failure to thrive and developmental delay. A gastrostomy tube was placed at 2 years of age. The combination of improved nutrition and optimal developmental therapy has led to her sitting supported, attempting to stand and enhancement of her cognitive and non-verbal communication abilities. Molecular investigation of the patient and her parents using microsatellite analysis has led to the conclusion that, as expected, the additional copy of chromosome 18 constituting the full trisomic cell line is maternal meiosis I in origin. The data, however, indicate that in the trisomic cell line containing the deleted chromosome 18q, the structurally abnormal 18 was of paternal origin. We think this case is the first described with both structural and numerical trisomic mosaicism involving chromosome 18 in a liveborn infant. We propose a mechanism of origin and review the literature, comparing the clinical presentation of this case with individuals having full or partial trisomy 18.