Antenatal detection of maternal unipartental disomy of chromosome 2 in a fetus with non-chromosomal, non-syndromic alobar holoprosencephaly

Low-level mosaic trisomy 2 at amniocentesis in a pregnancy associated with positive NIPT and CVS results for trisomy 2, maternal uniparental disomy 2, perinatal progressive decrease of the aneuploid cell line, cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, intrauterine growth restriction and a favorable fetal outcome

OBJECTIVE

We present low-level mosaic trisomy 2 at amniocentesis in a pregnancy associated with positive non-invasive prenatal testing (NIPT) and chorionic villus sampling (CVS) results for trisomy 2, maternal uniparental disomy (UPD) 2, perinatal progressive decrease of the aneuploid cell line, cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, intrauterine growth restriction (IUGR) and a favorable fetal outcome.

CASE REPORT

A 35-year-old, primigravid woman underwent amniocentesis at 16 weeks of gestation because both NIPT at 9 weeks of gestation and CVS at 11 weeks of gestation revealed trisomy 2. This pregnancy was conceived by in vitro fertilization (IVF) and embryo transfer (ET). Amniocentesis revealed a karyotype of 47,XY,+2[11]/46,XY[19]. Prenatal ultrasound findings were normal. She was referred to the hospital for genetic counseling at 20 weeks of gestation, and repeat amniocentesis performed at 24 weeks of gestation revealed a karyotype of 46,XY (22/22 colonies). The parental karyotypes were normal. Quantitative fluorescent polymerase chain reaction (QF-PCR) analysis on the DNA extracted from uncultured amniocytes and parental bloods revealed maternal uniparental heterodisomy of chromosome 2. Simultaneous molecular cytogenetic analysis on uncultured amniocytes showed the results of arr 2p25.3q37.3 × 2.4 with a log₂ ratio = 0.26, consistent with 40% mosaicism for trisomy 2 by array comparative genomic hybridization (aCGH), and 28% (28/100 cells) mosaicism for trisomy 2 by interphase fluorescence in situ hybridization (FISH). Despite IUGR on fetal ultrasound, the woman was advised to continue the pregnancy, and a 2252-g phenotypically normal male baby was delivered at 38 weeks of gestation. The karyotypes of cord blood, umbilical cord and placenta were 46,XY (40/40 colonies), 46,XY (40/40 colonies) and 47,XY,+2[9]/46,XY[31], respectively. QF-PCR analysis on cord blood, umbilical cord and placenta confirmed uniparental heterodisomy of chromosome 2 in the cord blood and umbilical cord, and maternal origin of trisomy 2 in the placenta. FISH analysis on buccal mucosal cells at age 1.5 months revealed 8.7% (9/104 cells) mosaicism for trisomy 2. When follow-up at age four months, the neonate manifested a normal phenotype except intermittent hypoventilation. Molecular analysis of the PHOX2B gene revealed a normal result. When follow-up at age one year, he manifested normal development.

CONCLUSION

Mosaic trisomy 2 at prenatal diagnosis should alert the possibility of UPD 2 and include a UPD 2 testing. Low-level mosaic trisomy 2 at amniocentesis can be associated with perinatal progressive decrease of the aneuploid cell line and a favorable fetal outcome.

A case of hyperphosphatemic familial tumoral calcinosis due to maternal uniparental disomy of a GALNT3 variant

Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare, inherited autosomal recessive disorder caused by fibroblast growth factor-23 (FGF23), N-acetylgalactosaminyltransferase 3 (GALNT3), or Klotho (KL) gene variants. Here, we report the case of a Japanese boy who presented with a mass in his left elbow at the age of three. Laboratory test results of the patient revealed normocalcemia (10.3 mg/dL) and hyperphosphatemia (8.7 mg/dL); however, despite hyperphosphatemia, serum intact FGF23 level was low, renal tubular reabsorption of phosphate (TRP) level was inappropriately increased, and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) level was inappropriately normal. Genetic analysis revealed maternal uniparental disomy (UPD) of chromosome 2, which included a novel GALNT3 variant (c.1780-1G>C). Reverse transcription-polymerase chain reaction (RT-PCR) analysis of GALNT3 mRNA confirmed that this variant resulted in the destruction of exon 11. We resected the mass when the patient was five years old, owing to its gradual enlargement. No relapse or new pathological lesions were observed four years after tumor resection. This is the first case report of a Japanese patient with HFTC associated with a novel GALNT3 variant, as well as the first case of HFTC caused by maternal UPD of chromosome 2 that includes the GALNT3 variant.

Prenatal diagnosis of complete maternal uniparental isodisomy of chromosome 4 in a fetus without congenital abnormality or inherited disease-associated variations

Background

The prenatal diagnosis of subjects with complete uniparental isodisomy of chromosome 4 (iUPD4) has rarely been reported and poses a great challenge for genetic counseling. In this study, a prenatal case with a high (1 in 58) risk of Down syndrome was diagnosed with iUPD4 by combined chromosomal microarray analysis (CMA), whole exome sequencing (WES) and ultrasound morphology scan.

Results

By CMA, a pathogenic copy number variant was not detected; however, a complete maternal iUPD4 was identified in this fetus after analyzing the parental genotype results. To detect potentially autosomal recessive variants, WES was performed. Two missense and two frameshift variants were identified but were predicted with uncertain significance; none of the mutations were definitively associated with congenital abnormality or inherited disease. In addition, a detailed ultrasound morphology scan did not identify any structural abnormalities, facial dysmorphisms or intrauterine growth restriction. The family history was unremarkable. The couple was counseled with the prenatal diagnostic results, and they opted to give birth to the child. No phenotypic abnormalities were observed in this child after the first year of life.

Conclusion

This study provides further evidence that iUPD4 can result in a healthy live birth and demonstrates that the combined use of CMA, WES and ultrasound technology provides additional information for the prenatal diagnosis and clinical management of rare UPD events.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-015-0190-z) contains supplementary material, which is available to authorized users.