Uncovering Rare Structural Chromosomal Rearrangements: Insights from Molecular Cytogenetics.

Complex chromosomal rearrangements (CCRs) are rare structural abnormalities involving at least three chromosomal breakpoints and often two or more chromosomes. Owing to their inherent genomic complexity, CCRs are frequently associated with abnormal phenotypes, including developmental delay, congenital anomalies, and infertility. In this study, we report four male patients, three of them with de novo rare structural chromosomal rearrangement detected through a combination of Giemsa-Trypsin (GTG) banding, fluorescence in situ hybridization (FISH), and high-resolution microarray techniques (SNP array and array CGH). Each of the four cases turned out to be of a different type: in addition to two exceptional CCRs, an inv dup del 18q and a cluster rearrangement involving the long arm of chromosome 4 were identified. Despite the limitations of the testing methods, we performed a detailed analysis of the relationship between the most detailed genotype data and the associated phenotype. Our study provides further valuable evidence that the use of molecular cytogenetic methods is of paramount importance even in cases with abnormal karyotypes detected by light microscopy, as high-resolution data may reveal unsuspected genomic complexity, which is essential for genetic counseling in these patients.