Cytogenetic studies were performed on 150 cases of Down's syndrome (DS) in Iran. The standard trisomy 21 was found in 132 (88 % ) and translocation-trisomy 21 (+21) in 18 (12%) patients, i.e., t(21,21) in 1(0.63%) and mosaicism in 17(11.33%) cases. The comparison of the frequencies for mosaicism between different populations such as Denmark, Hungary, Egypt, Iraq, India, Australia and Iran ...

Somatic mutations must happen often during development because of the large number of cell divisions to expand from a single-cell zygote to a full organism. A mutation in development carries forward to all descendant cells, causing genetic mosaicism. Widespread genetic mosaicism may influence diseases that derive from a few genetically altered cells, such as cancer. I show how to predict the ex...

Although mosaicism was shown to be a normal feature in cleaving embryos, its consequences for the late preimplantation stages are unknown. We performed blastocyst immunosurgery, followed by fluorescent in-situ hybridization (FISH), to determine the number of cells and degree of mosaicism in the inner cell mass (ICM) of human blastocysts. Of 47 ICM samples analysed, 20 had aneuploid cells, and t...

Introduction Gene mosaicism describes an individual who has developed from a single zygote and has two or more cell types with distinct genotypes. Three major types of mosaicism have been described and are referred as gonadal, somatic and gonosomic mosaicism. They mainly differ on the body distribution of the somatic mutation and in their clinical consequences. The recent use of next-generation...

Genetic aberrations are commonly seen in human preimplantation embryos. Non-disjunction and premature division of a chromosome are common in both meiosis and mitosis divisions. The expected result for meiotic aneuploidies is full aneuploidy in the later stages whereas mosaicism is the most frequent event in the cleavage and blastocyst stages. The main causes for mosaicism are post-zygotic event...

Embryonic mosaicism, defined as the presence of karyotypically distinct cell lines within an embryo, has been frequently reported with a high incidence in preimplantation embryos derived from IVF and is thought to be one of the major biological limitations for the routine application of PGD for aneuploidies (PGD-A). The incidence of mosaicism in preimplantation embryos is in fact reported to be...

Placental and fetal tissues from 46 human pregnancies were cultured and cytogenetically analyzed in an attempt to document the existence of chromosomal mosaicism confined strictly to tissues of extraembryonic origin. In two gestations in which chromosomal mosaicism was found, it was expressed exclusively in placental chorionic cells and was not detected in cells derived from the embryo proper. ...

Constitutional aneuploidy is typically caused by a single-event meiotic or early mitotic error. In contrast, somatic aneuploidy, found mainly in neoplastic tissue, is attributed to continuous chromosomal instability. More debated as a cause of aneuploidy is aneuploidy itself; that is, whether aneuploidy per se causes chromosomal instability, for example, in patients with inborn aneuploidy. We h...

We have analysed the CAG repeat in the Huntington disease (HD) gene in sperm and blood from 20 unrelated HD patients. Although the CAG repeat displayed significant mosaicism in sperm from all individuals, there were marked differences in the degree of repeat instability. Individuals who had either inherited or transmitted an expanded CAG repeat displayed the highest levels of repeat mosaicism, ...

There are increasing reports of multiple different types of somatic mosaicism detected in patients with inherited and non-inherited disorders. The characteristics of several of the major types of mosaicism will be outlined, and contrasted with somatic mosaicism, which is the focus of this article. This review examines examples of somatic mosaicism due to differences in DNA sequence arising from...