# Mosaic derivative chromosomes at chorionic villi (CV) sampling are expression of genomic instability and precursors of cryptic disease-causing rearrangements: report of further four cases

## TL;DR

This paper reports four cases where mosaic chromosomes in fetal and placental tissues show how genomic instability can lead to hidden genetic changes during early development.

## Contribution

The study adds four new cases showing how chromosomal instability in placental tissues can lead to de novo structural rearrangements.

## Key findings

- Mosaic derivative chromosomes in feto-placental tissues indicate genomic instability.
- Unbalanced chromosomes in placental tissues undergo extensive remodeling, leading to cryptic rearrangements.
- These findings highlight the role of placental tissues in the early selection of viable chromosomal arrangements.

## Abstract

Mosaic chromosomal anomalies arising in the product of conception and the final fetal chromosomal arrangement are expression of complex biological mechanisms. The rescue of unbalanced chromosome with selection of the most viable cell line/s in the embryo and the unfavourable imbalances in placental tissues was documented in our previous paper and in the literature. We report four additional cases with mosaic derivative chromosomes in different feto-placental tissues, further showing the instability of an intermediate gross imbalance as a frequent mechanism of de novo cryptic deletions and duplications. In conclusion we underline how the extensive remodeling of unbalanced chromosomes in placental tissues represents the ‘backstage’ of de novo structural rearrangements, as the early phases of a long selection process that the genome undergo during embryogenesis.