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

  • ️Fri Jan 01 2021

Case Reports

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

Wendy Shu et al. Genes (Basel). 2021.

Abstract

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.

Keywords: mosaicism; non-invasive prenatal test; normal phenotype; tetrasomy 9p.

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Conflict of interest statement

Sunny Wai Hung Cheung are employees of Xcelom (major service provider of cell-free DNA screening in Hong Kong and Macau). Wendy Shu, Shirley S.W. Cheng, Shuwen Xue, Lin Wai Chan, Sung Inda Soong, Anita Sik Yau Kan, and Kwong Wai Choy have no conflict interests to declare.

Figures

Figure 1
Figure 1

Blanschko’s line is evident on (a) the lower limbs and (b) over the abdomen; photograph taken when the patient was pregnant at 25 weeks of gestation.

Figure 2
Figure 2

Detection of increased counts of DNA originating from chromosome 9p by genome-wide cfDNA screening post-delivery day 6. The genomic position is shown on the x-axis and the count-based z-score is shown on the y-axis. Each open circle on the plot represents a 1-Mb window. The light blue–green vertical lines mark the boundaries of the centromere. Genome-wide cfDNA screening results: increased DNA from 9p24.3-p13.1:1-38,500,000, count-based z-score of 70.

Figure 3
Figure 3

Partial karyogram of cultured lymphocytes from peripheral blood of patients showing dic(9;9)(q21.1;q21.1).

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