PSEUDODICENTRIC CHROMOSOME 18 DIAGNOSED BY CHROMOSOME PAINTING AND PRIMED IN-SITU LABELING (PRINS)

We report on a newborn white male infant with marked dysmorphic featur es various congenital malformations. initial clinical evaluation showe d Crouzon-like features as well as some features of trisomy 18 syndrom e and trisomy 13 syndrome. The results from conventional cytogenetic a nalysis showed a structurally abnormal chromosome replacing one normal chromosome 18, but only by applying molecular cytogenetic methods cou ld the architecture of this abnormal chromosome be characterised clear ly. The primed in situ labelling (PRINS) technique, using a newly synt hesised alpha 18 oligonucleotide, showed the dicentric pattern and dir ect chromosome painting established the origin to be from chromosome 1 8. The combination of conventional cytogenetics and molecular cytogene tics showed the karyotype in the proband to be 45,XY,-14,-18,-21, + t( 14;21), + psu dic(18) (qter-->tcen-->tp11.3: :p11.3-->psu cen-->qter). This was supported by molecular analysis using chromosome 18 specific DNA markers, which showed the paternal origin of the abnormal chromos ome.