Diagnosis of microdeletion syndromes: high-resolution chromosome analysis versus fluorescence in situ hybridization

Contiguous gene syndromes are characterized by deletions or duplications of specific chromosomal segments involving clusters of single genes. Although these syndromes are associated with distinct clinical phenotypes, these features are difficult to distinguish in the newborn and early childhood periods. In such cases, demonstration of chromosomal involvement through cytogenetic studies is of vital importance in arriving at an accurate diagnosis. In this article results of microdeletion analysis of 31 cases comprising 16 cases of Prader-Willi syndrome, 3 of Angelman syndrome, 7 of Miller-Dieker syndrome, and 5 of DiGeorge syndrome are reported. All patients were studied with both high-resolution chromosome analysis and fluorescence in situ hybridization. In the majority of cases there is 100% concordance between the two techniques. However, in one patient suspected of having DiGeorge syndrome with a normal karyotype at the 750 band level, fluorescence in situ hybridization identified a deletion within the critical region. Without fluorescence in situ hybridization studies on this patient, it would not have been possible to confirm the diagnosis of DiGeorge syndrome cytogenetically. Based on these results and other studies reported in the literature, it is recommended that all suspected cases of microdeletion syndromes should be studied using fluorescence in situ hybridization, irrespective of high-resolution chromosome results. However, because of the difficulties associated with clinical diagnosis of these syndromes, fluorescence in situ hybridization should not replace standard chromosome analysis.