Background:
Copy number variations (CNVs) are largely known today, but their position is rarely established by fluorescence in situ hybridization (FISH) or karyotype analysis.
Case presentation:
We described two families with copy number gain in which FISH analysis with the specific subtelomeric probe of chromosome 4q and 7q evidenced a third signal at band 13p11.2. Genomic study by array comparative genomic hybridization defined the triple dose segment. In the first case, the duplicate tract is free of known genes, in the second one it contained three expressed genes.
Conclusions:
The CNV localization on the short arm of an acrocentric chromosome could explain the lack of phenotypic effect, being known the regulatory role of heterochromatin in the position-effect silencing. Furthermore, we would like to underline the importance of using complementary techniques such as FISH and array-CGH to obtain a better definition of genomic rearrangements.