Evaluation of the Abbott system in maternal serum screening for Down syndrome: the AxSym analyzer, AFP and hCG reagents and Maciel Prenatal Interpretive Software.

Multi-marker maternal serum screening for Down syndrome in the second trimester is now part of routine care in many centers. Most protocols use a combination of hCG (or its free beta-subunit) and alpha-fetoprotein (AFP) or unconjugated estriol (UE3), or both. Risk calculation is based on these maternal serum marker values combined with maternal age and trisomy 21 maternal age-related risk. Computer programs are therefore necessary. Both technical and statistical efficiency are included in the final risk evaluation. We studied the Abbott system, comprising AxSym analyzer, AFP and hCG kits and Prenatal Interpretive Software (Maciel). Median values were established between 14 and 18 weeks of amenorrhea in a population of 1822 patients and in twin pregnancies in 157 cases. Forty maternal sera from trisomy 21 affected pregnancies were analyzed. Software was evaluated in a population of 429 patients and in 124 cases of trisomy 21. We conclude that this system constitutes an accurate and efficient method of maternal serum screening for Down syndrome.

Parental origin of the extra chromosome in prenatally diagnosed fetal trisomy 21.

Trisomy 21 (Down syndrome) is one of the most common chromosomal abnormalities. Of cases of free trisomy 21 causing Down syndrome, about 95% result from nondisjunction during meiosis, and about 5% are due to mitotic errors in somatic cells. Previous studies using DNA polymorphisms of chromosome 21 showed that paternal origin of trisomy 21 occurred in only 6.7% of cases. However, these studies were conducted in liveborn trisomy 21-affected infants, and the possible impact of fetal death was not taken into account. Using nine distinct DNA polymorphisms, we tested 110 families with a prenatally diagnosed trisomy 21 fetus. Of the 102 informative cases, parental origin was maternal in 91 cases (89.2%) and paternal in 11 (10.8%). This percentage differs significantly from the 7.0% observed in previous studies (P<0.001). In order to test the influence of genomic parental imprinting, we determined the origin of the extra chromosome 21 in relation to different factors: advanced maternal age, maternal serum human chorionic gonadotropin (hormone of placental origin), severity of the disease, gestational age at diagnosis and fetal gender. We found that the increased frequency of paternal origin of nondisjunction in trisomy 21-affected fetuses cannot obviously be explained by factors leading to selective loss of paternal origin fetuses.

[Decrease of various enzyme activities in the amniotic fluid of the fetuses with chromosomal anomalies]. / Diminution de certaines activités enzymatiques dans le liquide amniotique de foetus porteurs d'anomalies chromosomiques.

The enzymatic activities of gamma-glutamyl-transpeptidase and of aminopeptidase M have been determined in amniotic fluids taken in pregnancies with a trisomic conceptus. The low values obtained in these fluids may be the consequence of fetal growth retardation.