Detection of fetal HLA-DQα sequences in maternal blood: A gender-independent technique of fetal cell identification

The objective of this study was to detect fetal HLA-DQα gene sequences in maternal blood. HLA-DQα genotypes of 70 pregnant women and their partners were determined for type A1. We specifically sought couples where the father, but not the mother, had genotype A1. In 12 women, maternal blood samples were flow-sorted. Candidate fetal cells were isolated and amplified by using PCR primers specific for a paternal HLA-DQα A1 allele. Fetal HLA-DQα A1 genotype was predicted from sorted cells; amniocytes or cheek swabs were used for confirmation. Six of twelve sorted samples had amplification products indicating the presence of the HLA-DQα A1 allele; 6/12 did not. Prediction of the fetal genotype was 100 per cent correct, as determined by subsequent amplification of amniocytes or cheek swabs. We conclude that paternally inherited uniquely fetal HLA-DQα gene sequences can be identified in maternal blood. This system permits the identification of fetal cells independent of fetal gender, and has the potential for non-invasive prenatal diagnosis of paternally inherited conditions.     

Expanding multiple marker screening for Down's syndrome to include Edward'S syndrome

Information on maternal age and maternal serum alpha-fetoprotein, unconjugated oestriol (uE₃), and human chorionic gonadotrophin (hCG) levels was used to investigate retrospectively the effect of estimating Edward's syndrome risk in women having multi-marker screening for Down's syndrome. The screened population comprised 15 pregnancies affected by Edward's syndrome, 15 with Down's syndrome and 5472 unaffected pregnancies. The use of all three markers to estimate Edward's syndrome risk would have led to the detection of 10–12 (67–80 per cent) cases with a false-positive rate of 0.3–0.6 per cent depending on the risk cut-off. A further case would have been detected as a result of screening for Down's syndrome alone. Similar results were obtained when the Edward's syndrome risk was based on uE₃ and hCG only. These data suggest that extending Down's syndrome screening to include Edward's syndrome risk will yield a high detection rate with only a small increase in the false-positive rate.     

Larval development in the Antarctic nemertean Parborlasia corrugatus (Heteronemertea: Lineidae)

Embryonic and larval development were followed from fertilisation to settlement in the Antarctic heteronemertean Parborlasia corrugatus (McIntosh, 1876). The first cleavage occurred 10 to 15 h after fertilisation, and the second at 17 h. Larvae hatched at the gastrula stage, between 170 and 200 h post-fertilisation, and were 150 m in diameter. Early larval stages aggregated in dense groups near the surface of incubation vessels and were positively phototactic. Early pilidium larvae were recognisable 435 h post-fertilisation. They were 155×152 m in size, and possessed a complete apical tuft of cilia and a full marginal band of locomotory cilia. At this stage, the gust was visible through the body wall, and the mouth was open and was 40 m in diameter. Late pilidia, 222×193 m in size, were helmet-shaped. They had an apical tuft over 100 m long, and possessed a lobed marginal band of locomotory cilia. Pilidia were observed aggregating close to the bottom of incubation vessels 1200 to 1350 h (50 to 56 d) after fertilisation, and this was interpreted as settlement behaviour. At this stage, the apical tuft had been lost and they were highly contractile, being capable of compressing their bodies. However, neither developing juveniles within the larval envelope nor hatched juveniles were observed. Pilidia consumed the microalgae Tetraselmis suecica, Thalassiosira pseudonana and Isochrysis galbana. They also fed on particulate organic material < 1 m in size, as shown by the presence of material in the guts of larvae offered filtered extracts of algal cultures. There was some indication that larvae could use dissolved organic material, since pilidia held in seawater with organic material removed did not survive as long as those in filtered seawater or in filtered water with added amino acids. However, the only larvae to exhibit settlement behaviour in the feeding experiments were those offered Tetraselmis succica and Thalassiosira pseudonana, and these required a longer development time to reach this stage than pilidia in the standard cultures, where a mixed algal diet was offered.