Trisomies are genetic disorders due to additional chromosome in the normal chromosome complement and are associated with distinctive phenotypic traits, different organ systems malformation and mental retardation. Trisomy 21 (Down syndrome) is the most frequent numerical chromosome disorder with an incidence of  1 in 700 newborns and is due to an extra 21 chromosome , an unbalanced translocations involving chromosome 21 or a duplication of a region of the chromosome[1-2].

Diagnosis of chromosomal abnormalities is usually performed by cytogenetic analysis but this tehnique requires a high number of cells for cultures, great tehnical expertise and to much time for performing (2-3 weeks) [3].

In 1993 Mansfield described for the first time an alternative molecular method for diagnosis of trisomies - the quantitative fluorescent polymerase chain reaction tehnique (QF-PCR) which is based on the amplification of highly polymorphic STR (short tandem repeats or microsatellites) markers specific for the chromosome involved in trisomy using fluorescent labeled oligonucleotides, followed by quantitative detection of amplified DNA signal by capillary elecrophoresis [4]. This tehnique has succesfully been applied for the detection of trisomies and described in a series of reports [3,5-7].

In this study we examined the amplification of D21S11 and Penta D STR loci on the chromosome 21 from ten 21 clinical diagnosed trisomic patients and five normal individuals using fluorescent PCR aiming to verify the medical diagnostic value of this tehnique. The patients were initially diagnosed by convetional cytogenetic tehnique. The samples were obtained after informed consent of the patients.