Tissue specificity of somatic mosaicism in constitutional trisomy of chromosome 8

Background. Constitutional trisomy 8 is a rare chromosomal abnormality in man. The exact incidence of trisomy 8 in live births remains unknown. Trisomy 8 is defined as the presence of three copies of chromosome 8 in every cell of an individual’s body—a condition that is usually causes the embryo death and is often detected in human spontaneous abortions. In instances of live births, trisomy 8 is predominantly associated with somatic mosaicism, with an estimated prevalence of 1:25 000 to 1:50,000, whose clinical presentation has a wide phenotypic variability Two cases are presented, demonstrating the tissue specificity of somatic mosaicism in constitutional trisomy 8, both in the presence and absence of clinically significant phenotypic abnormalities.

Aim: to assess the distribution and level of somatic mosaicism in tissues of different embryonic origins in mosaic trisomy 8 in two patients with abnormal phenotype and without specific clinical features.

Methods: conventional cytogenetic study, fluorescence in situ hybridization (FISH).

Results. The level of the abnormal clone in mosaic constitutional trisomy 8, as well as its distribution across various tissues, exhibited notable differences in a patient presenting with phenotype abnormalities and intellectual disability compared to case lacking clinically significant phenotype anomalies. It was observed that variability in the level of somatic mosaicism within tissues derived from the same embryonic lineage exists. Considering the tissue-specific nature of somatic mosaicism associated with trisomy 8, it is essential to investigate tissues originating from different germ layers when an abnormal clone is identified in the cells of a particular tissue.

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