Genotyping Platelet And Neutrophil Antigen Systems

Neonatal alloimmune thrombocytopenic purpura (NATP), the platelet counterpart of HDN, occurs with a frequency of approx 1 in 1100 live births (70). Infants affected with NATP are at risk of bleeding and 10-30% of cases develop intracranial hemorrhage (50% in utero), which can result in brain damage and lasting neurological sequelae. There are currently 25 different platelet-specific alloantigens and antigens shared with other tissues that have been implicated in causing NATP (Table 1). Maternal antibodies produced against the HPA-1a (PlA1) alloantigen are responsible for the vast majority (85%) of serologically confirmed NATP cases followed by antibodies against HPA-5b (Bra, 15%). However, unlike for HDN resulting from RHD, antenatal screening of women for HPA-1a is not performed, and there is no treatment equivalent to RhoGAM, although some maternal antenatal treatment regimens, including IV-immunoglobulin and/or steroids have been effective in reducing the incidence of infant intercranial hemorrhage (71). The severity of thrombocy-topenia in subsequent children born to a mother with a previous NATP-affected pregnancy is the same or greater and the mortality resulting from bleeding and intracranial hemorrhage is 1-3% in untreated cases, therefore, genotyping of the parents and fetuses in subsequent pregnancies provides important information to the obstetrician. For many years, platelet antigens could only be directly typed using serological methods. Discovery of the HPA-1a/b gene polymorphism by Newman et al. in 1989 (72) led to the development of several genotyping methods for all of the various platelet gene polymorphisms, recently reviewed by Hurd et al. (73). All but one of the platelet-specific alloantigens are the result of single-nucleotide polymorphisms (SNPs) in one of only five different platelet glycoprotein genes with 10 of the 18 mutations on the GPIIIa gene (Table 1). Genomic DNA isolated from fetal blood, amniocytes, or chorionic villus samples can be used successfully in ASPCR-based assays, which is currently the most commonly used method for platelet genotyping (5,73). As has been observed in the red cell antigen systems discussed earlier, variant alleles have been reported in the GPIIIa gene that result in discordance between the genotype and platelet phenotypes, but the occurrence of these unusual mutations appears to be rare (74-77).

Neonatal alloimmune neutropenia (NAN) is yet another immune cytopenic disorder involving immune destruction of fetal neutrophils by maternal IgG antibodies targeting paternally

Fig. 4. VNTR analysis of uncultured fetal amniocentesis samples using the D1S80 locus. In sets A-D the amplification products from 100% maternal DNA (M), 99% fetal DNA (F) mixed with 1% maternal DNA (M), and 100% fetal DNA (F) are shown. The assay sensitivity is 1% because of the detection of the maternal band in the 99% fetal DNA mixed with 1% maternal DNA lane. Maternal contamination of greater than 1% is not observed in these samples because of the absence of the maternal band in the 100% fetal DNA lane.

Fig. 4. VNTR analysis of uncultured fetal amniocentesis samples using the D1S80 locus. In sets A-D the amplification products from 100% maternal DNA (M), 99% fetal DNA (F) mixed with 1% maternal DNA (M), and 100% fetal DNA (F) are shown. The assay sensitivity is 1% because of the detection of the maternal band in the 99% fetal DNA mixed with 1% maternal DNA lane. Maternal contamination of greater than 1% is not observed in these samples because of the absence of the maternal band in the 100% fetal DNA lane.

inherited neutrophil alloantigens. The incidence of NAN has been reported to be 1 in 500 live births, with infants susceptible to infections following birth (78). Of the neutrophil alloantigens currently identified, the HNA-1a (NA1), HNA-1b (NA2), HNA-1c (SH), and HNA-2a (NB1) antigens are most often implicated in NAN (78) and are routinely typed using ASPCR (8,13,78).

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Pregnancy Guide

Pregnancy Guide

A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.

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