RAPID DETECTION OF FETAL ANEUPLOIDIES BY QUANTITATIVE FLUORESCENT-POLYMERASE CHAIN REACTION FOR PRENATAL DIAGNOSIS IN THE TURKISH POPULATION
Guzel AI, Yilmaz MB, Demirhan O, Pazarbasi A, Kocaturk-Sel S, Erkoc MA, Inandiklioglu N, Ozgunen FT, Sariturk C
*Corresponding Author: Associate Professor Ali Irfan Guzel, Department of Medical Biology and Genetics, Faculty of Medicine, Rize University, 53100, Rize, Turkey; Tel.: +90-464-212-30-09; Fax: +90- 464-212-30-15; E-mail: aliirfanguzel@hotmail.com
page: 11

RESULTS

The distribution of 31 pathological cases out of 1874 samples were as follow: 47,XX,+21 (19.4%, 6/31), 47,XY,+21 (48.4%, 15/31) 48,XXX,+21 (3.2%, 1/31), 69,XXX (3,2%, 1/31), 47,XY,+13 (3.2%, 1/31), 47,XXY (9.6%, 3/31), 47,XXX (9.6%, 3/31), 45,X (3.2%, 1/31). The ratio of heterozygous fl uorescent peak areas were close to 1:1 for normal cases (Figure 1) and 1:1:1 or 2:1 for aneuploidies of chromosome-specifi c STRs (Figure 2). At least two informative results for each chromosome-specifi c STRs were required to evaluate the prenatal diagnosis. Aneuploidic QF-PCR results were validated with cytogenetic analyses to complete the diagnosis. No false-positive results were observed, and all the pathological QF-PCR results were consistent with the cytogenetic analyses. Fetal sex and chromosome X and Y copy numbers were determined by amplifi cation of the non polymorphic AMXY sequences (generates chromosome X- and Y-specifi c products, differing 6 bp in length) and SRY, and other X- and Y-specifi c STRs (Table 1, Figure 1). These fi ndings were also in agreement with the cytogenetic analysis in all cases. In cases with uninformative results that have none or only one 1:1 ratio for a given chromosome, extra reaction mixture containing two or more additional STR primer sets specifi c for the chromosome of interest, were employed in order to obtain informative results. Maternal cell contamination was detected by evaluating peak patterns in heterozygous STRs as such, if there are three alleles and the sum of the peak areas of the two smaller alleles is equal to the largest peak area then the smaller of the two alleles is regarded as the maternal contaminant. The MCC sample results were clarifi ed by comparing the fetal STRs with maternal STRs obtained from maternal blood DNA samples (Figure 3). The X-specifi c product of the AMXY marker was found to be duplicated in three males producing fl uorescent peak areas in the ratio of 2 (for the X chromosome) and 1 (for the Y chromosome), 47,XXY males. In all X chromosome-related aneuploidies (one 45,X, three 47,XXX, and three 47,XXY cases), the correct diagnosis was achieved by using all of the X chromosome-specifi c STR markers. The diagnosis of Turnerís syndrome was based on the detection of a single QF-PCR product for all the X chromosomespecifi c polymorphic markers (data not shown). Of all markers studied, X22 and DXYS218 had the highest frequency of heterozygosity, therefore, regarded as the most informative markers. As for chromosomes 13, 18 and 21, STR markers, D13S258, D18S386 and D211414-1411 had the highest heterozygosity, respectively (Figure 4). In terms of additional chromosome markers studied, which were employed to validate the results obtained with regular STR markers having one or none informative markers for a specifi c chromosome, STR markers, D13S742, D18S858, D211412 and DX8377, had the highest heterozygosity for chromosomes 13, 18, 21 and XY, respectively, in our study population (Figure 5).



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