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.
Highlights
Tetrasomy 9p was first reported by Ghymers et al in 1973 [1]
The milder end of the disease spectrum has been shown with tissue-specific mosaicism of tetrasomy 9p, postulating that the severity of the phenotype may be related to the degree of mosaicism and the extent of tissues involvement [5]
Tetrasomy 9p has been described in two forms: isodicentric chromosome 9p (i(9p)), where the two short arms are linked by a single centromeric region, and pseudodicentric
Summary
Tetrasomy 9p was first reported by Ghymers et al in 1973 [1]. It is a rare chromosomal syndrome with typical features such as severe psychomotor retardation, skeletal and renal abnormalities, congenital heart disease, and facial dysmorphism [2]. Of all the reported cases with tetrasomy 9p mosaicism, approximately 50% of them show a characteristic facial appearance, growth impairment, and developmental retardation [4]. The milder end of the disease spectrum has been shown with tissue-specific mosaicism of tetrasomy 9p, postulating that the severity of the phenotype may be related to the degree of mosaicism and the extent of tissues involvement [5].
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