[Marker chromosomes as a product of familial translocation (11;22) identified with molecular cytogenetic methods].

A reciprocal constitutive 11;22 translocation is the most frequent, non Robertsonian translocation in man. We describe a case of partial trisomy 11q and 22q in a child with facial dysmorphy, hypotonia, heart failure, cryptorchism and psychomotor retardation. A marker chromosome was found in this child. Chromosome analysis with the fluorescence in situ hybridization, FISH technique showed that this marker chromosome was the product of 3:1 mejotic segregation of maternal (11;22) balanced translocation. Routine cytogenetic problems with identification of marker chromosomes can now successfully be solved with the FISH technique. The presented case clearly demonstrates the diagnostic usefulness of this newest method of cytogenetic analysis.