We report the successive application of classical Giemsa banding and chromosomal in situ suppression hybridization in clinical cytogenetics. The use of both techniques within one protocol requires an additional fixation of the chromosome preparations and an improved suppression of the labelled repetitive sequences. The combination of these two cytological techniques allows the high resolution mapping of translocated Y-chromosomal sequences in the chromosome set of an XX-male.

Metaphase chromosomes and interphase nuclei of chorionic villus samples (CVS) in five cases were studied after treatment with trypsin and post-fixation in formaldehyde by chromosomal in situ suppression (CISS) hybridization. Our modified protocol enables the use of in situ hybridization techniques on CVS preparations after 42 h of culture. A balanced translocation and trisomy 13 were identified with the aid of CISS hybridization.