Indentification of three different chromosomal additions by chromosome painting using fluorescence in situ hybridization [FISH] technique

Fluorescence in situ hybridization (FISH) is a very useful method for assessing chromosome rearrangements. When neither banding pattern nor clinical symptoms are sufficient to determine the origin of additional chromosomal fragment, FISH with multiple chromosome-specific libraries (chromosome painting), allows to solve this diagnostic problem rapidly. Three chromosomal additions, 7q+, 13p+ and 22q+, found in routine cytogenetic studies performed in children with phenotypic abnormalities were analysed using FISH. This technique documented the origin of the extra material to be derived from chromosome 16[der(7)t(7; 16)(q36.3;p 13.11)], 18[der(13)t(13; 18)(p12;q 12.2)] and 22[dup(22)(q11.2q13.1)], respectively. In two cases the abnormality arose de novo, while in the third case the product of translocation t(13;18) was maternal by origin. It was present in 30% of mother's lymphocytes, and in 70% of them a balanced Robertsonian translocation t(13q;15q) was found. In the presented cases the chromosome analysis with both traditional banding and chromosome painting techniques, allowed to establish final clinical diagnosis.