Rapid , Cost - effective Gene Mutation Screening for Car - nitine Palmitoyltransferase II Deficiency Using Whole Blood on Filter Paper , David Smail , Leah Gambino , Chris -

STR marker. Fourteen of these 19 pairs (74%) showed the presence of X-chromosomal DNA of paternal origin in maternal plasma (Table 1). Among the 14 third trimester sample pairs with informative STRs, the paternal allele could be detected in 10 (71%). A similar percentage was found for maternal plasma collected during the second trimester (80%; four of five). The earliest gestational age at which fetal DNA was detected was 16 weeks. These results suggested that STR analysis of maternal plasma could potentially be used for second trimester noninvasive prenatal diagnosis. Because the STR PCR systems used in this study amplified both the majority maternal alleles and the minority fetal alleles at the same time (10 ), the sensitivity of detecting the minority fetal allele was lower than in previous reports that utilized fetus-specific amplification schemes (2, 4, 9). The use of other types of polymorphisms, e.g., single nucleotide polymorphisms (11 ), which are amendable to allele-specific amplification strategies (12 ), should allow more sensitive systems to be developed. The use of five STR polymorphisms increased the chance that a fetomaternal pair would be informative. On average, 1.6 informative STR markers were found for each fetomaternal pair. If additional STRs are used, the chance of detecting the fetal alleles may be further increased. The use of multiple fluorescent labels and markers of easily distinguishable PCR product sizes may make it possible to perform this assay in a multiplex format, thus further increasing the speed and informativeness of the approach. Although the objective of this study was to demonstrate the detection of fetal-derived paternally inherited X-chromosomal polymorphisms in maternal plasma, the approach could easily be applied to autosomal polymorphisms. This development would potentially allow maternal plasma to be used for the noninvasive prenatal diagnosis of a wide variety of genetic disorders.