SNP array and phenotype correlation shows that FLI1 deletion per se is not responsible for thrombocytopenia development in Jacobsen syndrome.

Jacobsen syndrome (JBS) is a rare chromosomal disorder caused by terminal deletion of the long arm of chromosome 11. We report on four prenatally diagnosed patients with JBS with variable prenatal and postnatal phenotypes and 11q deletions of varying sizes. Precise characterization of the deleted region in three patients was performed by SNP arrays. The severity of both the prenatal and postnatal phenotypes did not correlate with the size of the haploinsufficient region. Despite the large difference in the deletion size (nearly 6 Mb), both of the live-born patients had similar phenotypes corresponding to JBS. However, one of the most prominent features of JBS, thrombocytopenia, was only present in the live-born boy. The girl, who had a significantly longer deletion spanning all four genes suspected of being causative of JBS-related thrombocytopenia (FLI1, ETS1, NFRKB, and JAM3), did not manifest a platelet phenotype. Therefore, our findings do not support the traditional view of deletion size correlation in JBS or the causative role of FLI1, ETS1, NFRKB, and JAM3 deletion per se for the development of disease-related thrombocytopenia.

Non-invasive fetal RHD exon 7 and exon 10 genotyping using real-time PCR testing of fetal DNA in maternal plasma.

OBJECTIVE: In this prospective study, we assessed the feasibility of foetal RHD genotyping by analysis of DNA extracted from plasma samples of Rhesus (Rh) D-negative pregnant women using real-time PCR and primers and probes targeted toward exon 7 and 10 of RHD gene. METHODS: We analysed 24 RhD-negative pregnant woman and 4 patients with weak D phenotypes at a gestational age ranging from 11th to 38th week of gestation and correlated the results with serological analysis of cord blood after the delivery. RESULTS: Non-invasive prenatal foetal RHD exon 7 genotyping analyses of maternal plasma samples was in complete concordance with the serological analysis of cord blood in all 24 RhD-negative pregnant women delivering 12 RhD-positive and 12 RhD-negative newborns. RHD exon-10-specific PCR amplicons were not detected in 2 out of 12 studied plasma samples from women bearing RhD-positive foetus, despite the positive amplification in RHD exon 7 region observed in all cases. In 1 case red cell serology of cord blood revealed that the mother had D-C-E-c+e+ C(w)- and the infant D+C-E-c+e+ C(w)+ phenotypes. RhD exon 10 real-time PCR analysis of cord blood was also negative. These findings may reflect that DC(w)- paternally inherited haplotype probably possesses no RHD exon 10. In another case no cord blood sample has been available for additional studies. The specificity of both RHD exon 7 and 10 systems approached 100% since no RhD-positive signals were detected in women currently pregnant with RhD-negative foetus (n = 8). Using real-time PCR and DNA isolated from maternal plasma, we easily differentiated pregnant woman whose RBCs had a weak D phenotype (n = 4) from truly RhD-negative patients since the threshold cycle (C(T)) for RHD exon 10 or 7 amplicons reached nearly the same value like C(T) for control beta-globin gene amplicons detecting the total DNA present in maternal plasma. However in these cases foetal RhD status cannot be determined. CONCLUSION: Prediction offoetal RhD status from maternal plasma is highly accurate and enables implementation into clinical routine. We suggest that safe non-invasive prenatal foetal RHD genotyping using maternal plasma should involve the amplification of at least two RHD-specific products.