Molecular cytogenetic evaluation of chromosomal microdeletions: the experience of a public hospital in Southern Brazil

Introduction: During the past few decades, the number of diseases identified to be caused by chromosomal microdeletions has increased quickly, bringing a new and crucial role for cytogenetics on the diagnosis of these conditions. The purpose of this study was to identify and characterize chromosomal microdeletions associated with malformation syndromes and intellectual disability. Methods: We retrospectively evaluated a consecutive series of samples from a cohort of 598 subjects with clinical symptoms of a microdeletion syndrome, including the deletion of chromosomes 4p16.3, 5p15.2, 5q35, 7q11.23, 8q24.12, 15q11.2, 16p13.3, 17p13.3, 17p11.2,2, and 22q11.2, as investigated by fluorescence in situ hybridization (FISH). Array-based comparative genomic hybridization (array-CGH) was performed on 25 samples with microdeletions. Results: A total of 598 samples were evaluated from patients whose clinical phenotypes were most indicative of 22q11.2 deletion syndrome (29.10%), Prader-Willi syndrome (23.41%), Angelman syndrome (16.89%), and Williams-Beuren syndrome (14.72%). In 142 of the samples (23.75%), a chromosomal imbalance associated with phenotypic abnormalities was found. The deletion of 7q11.23 was the most frequent (8.03%), followed by del22q11.2 (5.68%) and del15q11.2 (5%). Conclusion: Our study reinforces the idea that the effort to improve the capacity to perform molecular cytogenetic investigations associated with a qualified clinical evaluation is crucial for the detection and precise characterization of submicroscopic chromosome deletions, bringing benefits to patients, relatives, and genetic counselors. It also contributes to the continuing education of cytogeneticists and to the knowledge of chromosomal rearrangements associated with genomic disorders.