Structural chromosomal mosaicism and prenatal diagnosis

Abstract

True structural chromosomal mosaicism are rare events in prenatal cytogenetics practice and may lead to diagnostic and prognostic problems. Here is described the case of a fetus carrying an abnormal chromosome 15 made of a whole chromosome 2p translocated on its short arm in 10% of the cells, in association with a normal cell line. The fetal karyotype was 46,XX,add(15)(p10).ish t(2;15)(p10;q10)(WCP2+)[3]/46,XX[27]. Pregnancy was terminated and fetus examination revealed a growth retardation associated with a dysmorphism including dolichocephaly, hypertelorism, high forehead, low‐set ears with prominent anthelix and a small nose, which were characteristic of partial trisomy 2p. Possible aetiologies for prenatal mosaicism involving a chromosomal structural abnormality are discussed. Copyright © 2004 John Wiley & Sons, Ltd.

Multicolor-FISH Characterization of a Prenatal Mosaicism for a Chromosomal Rearrangement Undetected by Molecular Cytogenetics

“…However, some of these mosaic anomalies may involve structural chromosomal abnormalities. If most of these anomalies are sSMCs, mosaicism for balanced or unbalanced translocations is also observed [Stallings et al, 1997;Pipiras et al, 2004]. We report here a case of mosaicism in a fetus presenting with a major cell population showing partial monosomy 4q and a minor population with partial monosomy 4q plus partial trisomy 17q.…”

“…For these CVS, most mosaicisms are confined to the placenta [Grati et al, 2017], and only fetal sampling (e.g., AFS or cord blood samples) can prove true fetal mosaicism [Malvestiti et al, 2015]. Mosaicism can also be the consequence of culture artifacts [Pipiras et al, 2004]. Most fetal mosaicisms are aneuploidies [Grati et al, 2017] corresponding to mitotic, post-zygotic events, mainly due to 2 mechanisms: chromosome missegregation in a somatic cell of a euploid conceptus and trisomy or monosomy rescue after a meiotic nondisjunction [Taylor et al, 2014;Grati et al, 2017].…”

“…Mosaicism for small supernumerary marker chromosomes (sSMCs) is also described in prenatal samples and is involved in 14% of fetal mosaicisms [Grati et al, 2017]. Mosaicism may finally also involve structural chromosomal abnormalities and thus is observed for balanced or unbalanced translocations [Stallings et al, 1997;Pipiras et al, 2004;Malvestiti et al, 2015]. Mosaicism remains a challenge to diagnose, even with routine techniques of prenatal testing.…”