A Systematic Clinical Review of Prenatally Diagnosed Tetrasomy 9p

Genetic counseling of mosaic and non-mosaic tetrasomy 9p at prenatal diagnosis

Genetic counseling of mosaic and non-mosaic tetrasomy 9p remains difficult because of the possible associated congenital abnormalities, cytogenetic discrepancy in various tissues, true-positive and false-positive diagnosis in non-invasive prenatal testing (NIPT), uniparental disomy (UPD) 9, tissue-limited mosaicism, perinatal progressive decrease of the aneuploid cell line, phenotypic normal carriers and possible favorable fetal outcome in the cases with mosaic tetrasomy 9p at amniocentesis. This article presents a comprehensive review of various counseling issues concerning mosaic and non-mosaic tetrasomy 9p at prenatal diagnosis, and the information provided is very useful for genetic counseling under such circumstances.

Case Report: Prenatal diagnosis of fetal tetrasomy 9p initially identified by non-invasive prenatal testing

Tetrasomy 9p is a rare syndrome characterized by fetal growth restriction, Dandy-Walker malformation, cardiac anomalies, and facial abnormalities and is discovered by ultrasound during the prenatal examination. Herein, we report a fetus of tetrasomy 9p without obvious phenotypic manifestations during the first trimester that was identified by non-invasive prenatal testing (NIPT). NIPT revealed that the gain of 9p24.3–9p11 that was approximately 46.36 Mb in size. Karyotyping of amniocytes indicated an additional marker in all metaphase. Chromosome microarray and fluorescence in situ hybridization on uncultured amniocytes revealed tetrasomic of 9p24.3q13, and that the supernumerary chromosome is a dicentric isochromosome consisted of two copies of the 9p arm. Taken together, it was indicated that the fetal karyotype was 47,XY,+idic (9) (q13), and that multiple techniques are crucial to the prenatal diagnosis.

Cases of tetrasomy 9p and trisomy 9p in prenatal diagnosis—Analysis of noninvasive and invasive test results

Objective: Tetrasomy 9p and trisomy 9p are rare chromosomal aberrations. The phenotypes of tetrasomy 9p and trisomy 9p are variable. Most cases are diagnosed in the postnatal period. The study aims to analyze the prenatal phenotype of tetrasomy 9p and trisomy 9p in terms of ultrasound and screening tests.

Methods: A set of 1573 prenatal tests performed from 2016 to 2021 was reviewed to identify all cases with trisomy 9p and tetrasomy 9p. In four cases with 9p gain, non-invasive and invasive test results were analyzed.

Results: Four cases with the 9p gain were diagnosed in the prenatal period: two cases with tetrasomy 9p and two cases with trisomy 9p. Nasal bone hypoplasia and ventriculomegaly are common features of 9p gain. In two out of four cases with the 9p gain, an increased risk of trisomy 21 was found in the combined first-trimester screening test.

Conclusion: Trisomy 9p and tetrasomy 9p are characterized by a variable phenotype in the prenatal period, manifesting in genetically abnormal fetuses. The tetrasomy 9p and trisomy 9p may suggest trisomy 21 in the first trimester.

Tetrasomy 9p, a Prenatal Challenge: Two Novel Cases

Tetrasomy 9p is a chromosomal disorder characterized by the presence of a supernumerary chromosome. This rare abnormality exhibits a broad phenotypic variability and is not clearly distinguishable from other more frequent aneuploidies in the prenatal setting. We present two prenatal cases with dissimilar phenotypes, one with solely increased fetal nuchal translucency and one with multiple congenital anomalies, and discuss prior studies. These cases illustrate the difficulty of prenatally diagnosing this condition based on phenotypic information alone. We conclude that invasive prenatal diagnosis with (molecular) karyotyping is the best choice for the prenatal detection of tetrasomy 9p.

Prenatal diagnosis of a case with tetrasomy 9p confirmed by cytogenetics, FISH, microarray analysis and review

OBJECTIVE

Tetrasomy 9p is a rare fetal condition. Cases are usually mosaic. Here, we present a non-mosaic tetrasomy 9p case with cytogenetic analysis, fluorescence in situ hybridization, microarray data, ultrasound findings, and phenotypic presentation.

CASE REPORT

A pregnancy was referred to cytogenetic analysis because of increased nuchal translucency in prenatal ultrasound at 13 weeks of gestation. Prenatal laboratory analysis revealed an extra marker chromosome with a non-mosaic pattern. Ultrasonographic findings were unilateral cleft lip and palate, micrognathia, and atrioventricular septal defect at the 17th week; additionally, ventriculomegaly, left axis deviation of the fetal heart, and a single umbilical artery were determined at the 23rd week.

CONCLUSION

Phenotypic severity in non-mosaic tetrasomy 9p widely differs depending on the chromosomal content. We recommend performing appropriate genetic tests in those pregnancies with the suspicion of tetrasomy 9p, evaluating the mosaic state, and following those cases with detailed ultrasonographic examinations.

First Case Report of Maternal Mosaic Tetrasomy 9p Incidentally Detected on Non-Invasive Prenatal Testing

Tetrasomy 9p (ORPHA:3390) is a rare syndrome, hallmarked by growth retardation; psychomotor delay; mild to moderate intellectual disability; and a spectrum of skeletal, cardiac, renal and urogenital defects. Here we present a Chinese female with good past health who conceived her pregnancy naturally. Non-invasive prenatal testing (NIPT) showed multiple chromosomal aberrations were consistently detected in two sampling times, which included elevation in DNA from chromosome 9p. Amniocentesis was performed and sent for chromosomal microarray, which was normal. Maternal karyotype revealed that mos 47,XX,+dic(9;9)(q21.1;q21.1)(24)/46,XX(9) presents mosaic tetrasomy for the short arm of chromosome 9p and is related to the NIPT results showing elevation in DNA from chromosome 9p. The pregnancy was uneventful, and the patient was delivered at term. Maternal samples were obtained at two different time points after delivery showed the same multiple chromosomal aberrations detected during pregnancy. This is a first report on an unusual case of mosaic isodicentric tetrasomy 9p in a healthy adult with normal intellect. With widespread adoption of NIPT for screening fetal aneuploidy and genome-wide copy number changes, a rise in incidental detection of maternal rare genetic syndrome will bring challenges in our current approach to genetic counselling and prenatal diagnosis.