# Cytogenetically Balanced Reciprocal Translocation Could Hide Molecular Genomic Unbalances: Implications for Foetal Phenotype Correlation

## TL;DR

A seemingly balanced genetic change in a fetus can actually hide a genomic imbalance, affecting prenatal diagnosis and risk assessment.

## Contribution

Highlights the need for molecular testing alongside karyotype analysis in prenatal diagnosis of chromosomal abnormalities.

## Key findings

- A cytogenetically balanced translocation was found to be genomically unbalanced.
- The case shifted the risk from Down syndrome to Zellweger syndromic spectrum due to a PEX3 deletion.
- A healthy baby was born despite the initial concerns.

## Abstract

When an increased nuchal translucency (>3.00 mm) is observed during the echographic examination of a foetus in the first trimester of pregnancy, an increased risk of chromosomopathy is considered, and the pregnant woman is offered the possibility of an invasive investigation. Here, we focused our attention on prenatal diagnosis issues in cases of foetuses with cytogenetically balanced reciprocal translocations. We report the finding of a cytogenetically balanced, de facto genomically unbalanced translocation that poses a challenge in a case of prenatal diagnosis, changing the risk of Down syndrome in a Zellweger syndromic spectrum risk (PEX3 deletion). At term, a healthy baby was born. This case teaches that prenatal diagnosis in cases of foetuses at increased risk of chromosomal abnormality imperatively requires molecular investigation in addition to a morphological karyotype.