Prenatal diagnosis of low‐level mosaic tetrasomy 9p by amniocentesis

Sonographic findings in a case of tetrasomy 9p associated with increased nuchal translucency and Dandy‐Walker malformation

“…5 The wide phenotypic differences in individuals affected by tetrasomy 9p can be attributed to the degree of mosaicism, the size of the isochromosome involved, and the presence of tissue-limited mosaicism. 5 The variation in phenotypic expression in tetrasomy 9p ranges from normal individuals to multiple anomalies. Several authors correlated the variability and severity of the phenotype to the degree of mosaicism.…”

“…3 Also, the isochromosome 9p shows a strong propensity for tissue selection, and its detection may be difficult in cytogenetic prenatal diagnostic studies. 5,[9][10][11] In fact, prenatal diagnosis of tetrasomy 9p remains uncommon. There are approximately only 12 previous cases of tetrasomy 9p diagnosed prenatally because the abnormal chromosome is more frequently detected in peripheral blood cultures and can be absent in skin, amniotic fluid, or chorionic villous cell cultures.…”

“…2,3 There is a wide variety of phenotypic expressions for tetrasomy 9p 2,4 that can be attributed to the degree of mosaicism, the size of the isochromosome involved, and the presence of tissue-limited mosaicism. 5 One of the anomalies previously reported in infants with tetrasomy 9p is Dandy-Walker malformation, a disorder of the development of the cerebellum that has been associated with a variety of genetic syndromes and chromosomal abnormalities. A variety of other chromosomal disorders have been reported in association with abnormal cerebellar development, including trisomies 9, 13 and 18, triploidy, and Turner syndrome.…”

Prenatal diagnosis and findings of tetrasomy 9p

“…However, array comparative genomic hybridization (aCGH) studies on DNA extracted from peripheral blood lymphocytes and saliva showed that the patient had tissue‐specific mosaicism, with a lower level of abnormal cells in the saliva, further supporting the fact that missing the abnormality prenatally by amniocentesis or chorionic villus sampling is a concern . Yet a case of prenatally diagnosed low‐level mosaic (mos 47,XX,+idic(9)(pter → q12:q12 → pter)[4]/46,XX[16]) by amniocentesis has been previously reported . Coman et al .…”

“…10 Yet a case of prenatally diagnosed low-level mosaic (mos 47,XX,+idic(9)(pter → q12:q12 → pter) [4]/ 46,XX [16]) by amniocentesis has been previously reported. 12 Coman et al 13 reported a single case of confined placental mosaicism for tetrasomy 9p on chorionic villus sampling following sonographic finding of thickened nuchal translucency (8.2 mm, 5.58 multiples of the median). Amniocentesis and fetal blood sample showed normal female karyotype 46, XX.…”