Origin of nondisjunction in trisomy 8 and trisomy 8 mosaicism.

Causes of chromosomal nondisjunction is one of the remaining unanswered questions in human genetics. In order to increase our understanding of the mechanisms underlying nondisjunction we have performed a molecular study on trisomy 8 and trisomy 8 mosaicism. We report the results on analyses of 26 probands (and parents) using 19 microsatellite DNA markers mapping along the length of chromosome 8. The 26 cases represented 20 live births, four spontaneous abortions, and two prenatal diagnoses (CVS). The results of the nondisjunction studies show that 20 cases (13 maternal, 7 paternal) were probably due to mitotic (postzygotic) duplication as reduction to homozygosity of all informative markers was observed and as no third allele was ever detected. Only two cases from spontaneous abortions were due to maternal meiotic nondisjunction. In four cases we were not able to detect the extra chromosome due to a low level of mosaicism. These results are in contrast to the common autosomal trisomies (including mosaics), where the majority of cases are due to errors in maternal meiosis.

Apolipoprotein E epsilon4 allele as a genetic risk factor for left ventricular failure in homozygous beta-thalassemia.

In homozygous beta-thalassemia, the organ damage is mainly attributed to excessive iron deposition through the formation of oxygen free radicals. Despite appropriate transfusion and chelation therapy and low ferritin levels, patients still develop organ failure, heart failure being the main cause of death. This study was designed to determine whether the decreased antioxidant activity of the apolipoprotein E (APOE) 4 allele could represent a genetic risk factor for the development of left ventricular failure (LVF) in beta-thalassemia homozygotes. A total of 251 Greek beta-thalassemia homozygotes were studied. Patients were divided in three groups: group A (n = 151) with no cardiac impairment, group C (n = 47) with LVF, and 53 patients with LV dilatation and normal LV systolic function constituted the group B. DNA was obtained from all patients, and the polymerase chain reaction was used to analyze the polymorphism at the APOE locus. The APOE allele frequencies were compared with those of a Greek control sample of 216 healthy blood donors. Patients with no cardiac impairment had an APOE 4 allele frequency (7.9%) not different from population controls (6.5%, P > .05), while patients with LVF had a significantly higher frequency of APOE 4 (12.8%) than the controls (P < .05, odds ratio = 2.11, 95% confidence interval 1.03 to 4.32). The APOE 4 allele may represent an important genetic risk factor for the development of organ damage in homozygous beta-thalassemia.

Analysis of the origin of the extra chromosome in trisomy 8 in 4 cases of spontaneous abortions.

OBJECTIVE: To determine the origin of the extra chromosome in trisomy 8 in spontaneous abortions. METHODS: We analyzed 4 cases of nonmosaic trisomy 8 in 1st-trimester spontaneous abortions and their parents with DNA polymorphism analysis using microsatellite DNA markers. RESULTS: In 3 cases the extra chromosome was maternal in origin and in 1 case paternal in origin. In 2 of the cases the nondisjunction had occurred in maternal meiosis, while the other 2 cases were consistent with a postzygotic (mitotic) origin of the additional chromosome. CONCLUSION: Although a small number of cases studied, these results suggest differences from the common autosomal trisomies 21, 18, 16, and 13 where the vast majority of cases are due to errors in maternal meiosis.

Origin and mechanisms of non-disjunction in human autosomal trisomies.

Chromosomal aneuploidy is one of the major causes of pregnancy wastage. In this review we summarize the knowledge about the origin and mechanisms of non-disjunction in human autosomal trisomies 8, 13, 15, 16, 18, and 21, accumulated during the last decade by using DNA polymorphism analysis. Maternal meiosis I non-disjunction is the most important single class, but chromosome-specific patterns exist. For the acrocentric chromosomes 15 and 21, meiosis I errors predominate among the maternal errors, in contrast to trisomy 18 where meiosis II errors predominate. For trisomy 16, virtually all cases are due to maternal meiosis I non-disjunction. Postzygotic (mitotic) non-disjunction constitutes 5-15% of cases of trisomies 15, 18, and 21, whereas for trisomy 8 and trisomy 8 mosaicism the majority of cases are due to mitotic non-disjunction. For paternal non-disjunction of chromosomes 18 and 21, meiosis II or mitotic errors predominate. There is aberrant meiotic recombination associated with maternal meiotic non-disjunction in all trisomies studied in detail so far. Advanced maternal age remains the only well documented risk factor for maternal meiotic non-disjunction, but there is, however, still a surprising lack of understanding of the basic mechanism(s) behind the maternal age effect.

Common iliac artery flow velocity waveforms in fetuses with a single umbilical artery: a longitudinal study.

OBJECTIVES: In fetuses with a single umbilical artery the entire blood flow to the placenta is transported through the common and internal iliac arteries from the side of the single artery, whereas the pelvic vessels from the side of the missing artery do not participate in the fetoplacental circulation. The aim of this study was to investigate the effect of gestational age on pelvic arterial blood flow in fetuses with single umbilical artery. DESIGN: In 15 fetuses with a single umbilical artery (SUA), common iliac artery flow velocity waveforms were studied longitudinally using high resolution colour Doppler ultrasonography at three gestational ages: 18 to 20 weeks, 28 to 30 weeks, and 35 to 37 weeks. The pulsatility index was measured in each common iliac artery and mixed model analysis of variance was used to examine the effect of gestational age and side. RESULTS: There was a highly significant difference in pulsatility index between common iliac arteries at all gestational ages, the values always being higher on the side that did not participate in the fetoplacental circulation (P < 0.001). For increasing gestation, the pulsatility index fell significantly in the SUA side but remained high in the non-SUA side (P < 0.001). CONCLUSIONS: This study shows that the asymmetry in the pelvic arterial blood flow in fetuses with SUA increases as pregnancy progresses, consistent with decreasing vascular resistance in the placenta and increasing resistance in the lower extremities.

Second-trimester echogenic bowel and intraamniotic bleeding: association between fetal bowel echogenicity and amniotic fluid spectrophotometry at 410 nm.

OBJECTIVE: Our purpose was to determine whether the presence of heme pigments in amniotic fluid is associated with the ultrasonographic findings of increased fetal bowel echogenicity in the second trimester. STUDY DESIGN: Spectrophotometric analysis of amniotic fluid for optical density at 410 nm was prospectively performed to study the presence of heme pigments in (1) 104 pregnancies undergoing second-trimester amniocentesis for routine cytogenetic indications and (2) in 14 pregnancies undergoing amniocentesis for prenatal karyotyping because of fetal strongly echogenic bowel. In the routine amniocentesis group the fetal small bowel echogenicity was assessed immediately before amniocentesis and classified as nonechogenic (n = 64), mildly echogenic (n = 36), or hyperechogenic (n = 4) with the fetal iliac wing and liver used as references. Only amniotic fluid specimens that were obtained at the first attempt and that were not blood-stained were included in this study, with the first milliliter being discarded in all samples. RESULTS: In the routine amniocentesis group abnormal amniotic fluid optical density readings were significantly more frequent in fetuses with increased bowel echogenicity compared with those with nonechogenic bowel (8/40 [20%] vs 3/64 [5%], respectively; p < 0.001). In the hyperchogenic bowel group abnormal amniotic fluid optical density readings were found in four samples (29%). Overall, 12 of 54 fetuses (22%) with increased bowel echogenicity had a detectable peak at 410 nm. Three of the 12 (25%) fetuses with echogenic bowel and positive readings for hemoglobin were chromosomally abnormal. CONCLUSIONS: Fetal small bowel echogenicity is associated with the presence of heme pigments in amniotic fluid as determined by amniotic fluid optical density at 410 nm. Swallowing of amniotic fluid after intraamniotic bleeding seems implicated in the etiology of second-trimester echogenic bowel in both euploid and aneuploid fetuses.

Is isolated second-trimester hyperechogenic bowel a predictor of suboptimal fetal growth?

Hyperechogenic bowel has been described as a normal variant in second-trimester fetuses, but also in association with cystic fibrosis, chromosomal abnormalities, congenital infection, intestinal obstruction and intra-amniotic bleeding. These fetuses are also at risk for poor perinatal outcome, mainly due to intrauterine growth retardation. In this report we examine the potential of ultrasonographic detection of isolated fetal hyperechogenic bowel in the second trimester as a marker of subsequent suboptimal fetal growth. Second-trimester fetuses with hyperechogenic bowel in comparison to controls had a greater incidence of birth weight below the 10th centile (6/48, 12.5% vs. 4/149, 2.7%, respectively; p = 0.01) and lower mean birth weight (3176 g (SD 741 vs. 3499 g (SD 493)), respectively; p = 0.001). There was no difference in the prevalence of preterm delivery in both groups (3/48, 6.3% vs. 8/149, 5.4%, respectively; p = 0.7). This study suggests that second-trimester fetuses normally-grown with isolated hyperechogenic bowel are at risk for suboptimal fetal growth.

Discordant blood flow velocity waveforms in left and right brachial arteries in growth-retarded fetuses.

OBJECTIVE: To determine if the increase in cerebral blood flow ("brain-sparing" effect) with fetal hypoxemia is associated with discordant hemodynamics in the upper extremities. METHODS: We studied 12 fetuses with severe growth retardation, absent or reverse end-diastolic blood flow in the umbilical artery, and low pulsatility index (PI) in the middle cerebral artery, and 12 appropriately grown control fetuses with normal fetoplacental Doppler studies. The right and left brachial arteries were identified by high-resolution color Doppler ultrasonography, and the PI was measured in each brachial artery. RESULTS: All growth-retarded fetuses had lower impedance indices in the right than in the left brachial artery (mean delta PI 1.0, 95% confidence interval [CI] 0.7-1.3, P < .001). No differences in the brachial artery impedance indices were found in control fetuses matched for gestational age (mean delta PI 0.0, 95% CI -0.2 to 0.2). CONCLUSIONS: Left and right brachial artery blood flow velocity waveforms are discordant in fetuses with growth retardation and cerebral vasodilation. Because the right arm receives its blood supply from the same source as the brain (brachiocephalic artery) and given the proximity of the left subclavian artery to the ductus arteriosus, we speculate that this might be the result of increased blood flow into the brachiocephalic circulation and/or functional differences in the distribution of left and right ventricular output within the aortic arch in response to fetal hypoxemia.

Fetal cholecystomegaly: a prenatal marker of aneuploidy.

The fetal gall bladder can now be easily identified during the second and third trimesters using high-resolution ultrasonography. In this report we present eight fetuses with an enlarged gall bladder detected on prenatal ultrasonography at a mean gestational age of 24.6 weeks (range 19-31 weeks). Additional ultrasonographic findings were present in four cases: fetal anomalies and intrauterine growth retardation in three and polyhydramnios in one. Of those cases associated with fetal anomalies, one women underwent amniocentesis at 21 weeks revealing trisomy 18. The other two declined prenatal karyotyping; neonatal karyotyping revealed trisomy 13 in one and trisomy 18 in the other. Although an enlarged fetal gall bladder can be a normal variant in the second and third trimesters, the prenatal detection of cholecystomegaly should prompt a search for associated anomalies and other markers of aneuploidy. If found, prenatal karyotyping should be considered.

True knot of the umbilical cord: a difficult prenatal ultrasonographic diagnosis.

We examined retrospectively the use of ultrasonography in 18 cases in which a true knot of the umbilical cord was found at delivery. All women had a normal second-trimester scan in which no cord abnormality was detected. Thirteen (72%) also had third-trimester color Doppler ultrasonography, at which time the cord anomaly was again missed. In one of these cases the diagnosis could have been made with color flow imaging, but the abnormal pattern was mistaken instead for multiple loops of cord. On the other hand, the diagnosis of true knot was considered prenatally in two cases, but not confirmed at delivery, when only a prominent false knot was found in one and a normal cord in the other. We conclude that true knots of the umbilical cord do not have a characteristic appearance in utero and therefore are easily missed at routine prenatal ultrasonography.

Fetal heart rate response to vibroacoustic stimulation during low and high heart rate variability episodes in late pregnancy.

In 52 women in late pregnancy, the mean durations of transient fetal tachycardia after vibroacoustic stimulation during low fetal heart rate variability (4.8 minutes) and high fetal heart rate variability (6.3 minutes) were similar. The fetal heart rate continued with high variability in all cases, suggesting that the fetus did not return to its prestimulation state after vibroacoustic stimulation during quiescence. In 10 women, the duration of high variability after vibroacoustic stimulation during low fetal heart rate variability was significantly shorter (mean, 22 minutes) than the preceding (mean, 36 minutes) or subsequent (mean, 43 minutes) high-variability components of complete rest activity cycles. In another 10 women, the duration of high variability after vibroacoustic stimulation during high fetal heart rate variability was similar to preceding and subsequent high-variability episodes. In these 20 women, the next complete rest-activity cycle after vibroacoustic stimulation was not different in duration to the complete cycle recorded on the previous day.

Fetal blood sampling from the intrahepatic vein for rapid karyotyping in the second and third trimesters.

One hundred and twelve fetuses with structural anomalies (n = 84), intrauterine growth retardation (n = 21) or amniotic fluid volume disorders (n = 7) detected by ultrasound underwent blood sampling from the intrahepatic vein for rapid karyotyping. The procedure was successful in 95.5%. 12.5% of the fetuses had an abnormal karyotype. Fetal bradycardia was observed in two fetuses (1.8%) and intraperitoneal bleeding in three (2.7%). There were three procedure-related losses but these were not due to the intrahepatic vein sampling itself. Fetal blood sampling is the method of choice for rapid karyotyping in the second and third trimesters, and the intrahepatic vein is an alternate site when access is difficult or failure to sample occurs at the placental cord insertion. Additional advantages of fetal blood sampling at the intrahepatic vein include absence of cord complications, reduced risk of fetal blood loss and fetomaternal haemorrhage, and the lack of need to confirm the fetal origin of the sample.

Efficacy and safety of aztreonam in the treatment of patients with renal failure.

The efficacy and safety of aztreonam for treatment of gram-negative bacterial infections in patients with renal failure were evaluated in an open study. Thirty-nine patients (22-82 years old) with renal failure (chronic, 25; acute, 14) were treated for 40 severe gram-negative bacterial infections. All 41 gram-negative pathogens isolated were sensitive to aztreonam; the pathogens included Escherichia coli (12), Pseudomonas aeruginosa (8), Klebsiella species (7), Proteus species (7), Enterobacter species (5), Serratia marcescens (1), and Acinetobacter species (1). Complete cure (clinical and bacteriologic) was achieved in 31 (77.5%) of 40 infections and improvement (clinical improvement with or without bacteriologic cure) in four (10%). Bacterial eradication of 34 (82.9%) of the infecting pathogens was achieved. The only significant adverse effect noted was a slight, transient elevation in the level of serum transaminases in four patients (10%). Renal function of the patients improved with treatment. Levels of serum creatinine decreased from 3.79 +/- 2.84 to 3.30 +/- 2.52 mg/dL after treatment (P less than .002). It was concluded that aztreonam is effective and safe for the treatment of gram-negative bacterial infections in patients with renal failure.

The effect of intrauterine intravascular blood transfusion on iron metabolism in fetuses with Rh alloimmunization.

Fetal plasma ferritin concentrations were measured in 43 normal fetuses at 18-36 weeks and in 78 blood samples collected before transfusion from 23 fetuses with Rh alloimmunization. Among controls, there was a significant correlation between fetal serum ferritin and gestational age (r = 0.39, P = .009), consistent with an increase in fetal storage of iron during normal pregnancy. In Rh-alloimmunized fetuses, the ferritin concentration was above the reference range in 63% of the samples. Before the first transfusion, the fetal ferritin concentration was increased compared with controls (mean multiples of the mean = 2.6, range 1-26) and showed a negative correlation with fetal hematocrit (r = -0.43, P less than .05), suggesting that the worse the fetal anemia, the higher the iron store. Serial transfusions were associated with further increase in serum ferritin, which correlated primarily with the total volume of blood transfused. Three fetuses had plasma serum ferritin concentrations above 1 mg/L, a level compatible with a diagnosis of iron overload in children. These observations suggest that there is a potential risk of iron overload in Rh-alloimmunized fetuses undergoing intrauterine blood transfusion.

Further predictors of renal dysplasia in fetal obstructive uropathy: bladder pressure and biochemistry of 'fresh' urine.

Urine was aspirated on two consecutive days from the dilated bladder of nine fetuses with lower urinary tract obstruction. Gestational age ranged from 17 to 35 weeks. Renal dysplasia was diagnosed histologically in four fetuses, whereas the other five had normal renal histology or only partial dysplasia. Urinary sodium (Na+) and osmolality (Osm) decreased significantly in the second urine sample 1 day after bladder emptying (median decrease: Na+ = -11.3 per cent; Osm = -13.3 per cent). Although there were no significant differences between fetuses with or without renal dysplasia, normalization of an initially raised urine Na+ concentration occurred at the second sample in a fetus with partially normal renal histology, thus correcting a false-positive diagnosis of dysplasia. Bladder pressure was measured at the time of the first urine sampling in seven fetuses and in a further eight with bladder outlet obstruction undergoing a single urine aspiration at 18-28 weeks. Bladder pressure was increased above the reference range in 8 of 15 fetuses with urinary obstruction, but there was no correlation between pressure and the degree of impairment of renal function. Although no conclusive clinical guidelines can be drawn from this study for the evaluation of fetal renal function, these findings suggest that, in lower urinary tract obstruction, tubular reabsorption is impeded by the standing pressure in the urinary tract and that improvement of renal function may occur following relief of obstruction.

Fetal liver dysfunction in Rh alloimmunization.

The liver enzymes, aspartate transaminase (AST), alanine transaminase (ALT), gamma glutamyl transpeptidase (GGT) and alkaline phosphatase (ALP), were measured in the blood of 25 fetuses with severe Rh alloimmunization at the time of their first, second and third intravascular transfusions and in 17 comparison fetuses. In the comparison group, GGT increased with advancing gestation (r = 0.7; P = 0.002), whereas ALP, AST and ALT did not correlate with gestational age. Rh hydropic fetuses (n = 8) had higher blood ALT levels than the comparison fetuses (P = 0.008) had significantly increased transaminases when compared with non hydropic fetuses (n = 17). In hydropic fetuses, AST correlated with the nucleated red cell count before transfusion (r = 0.94; P = less than 0.0001). Fetal transaminases were no longer increased in hydropic fetuses by the second (AST) or third (ALT) transfusion. In both hydropic and non hydropic fetuses, GGT increased by the second transfusion (median percentage change +85%, range -83% to +596%; P = 0.003). The rise in fetal GGT was transitory and correlated with the increase in fetal haematocrit at the first transfusion (r = 0.58; P = 0.006). This study reports liver dysfunction secondary to extramedullary erythropoiesis in Rh alloimmunization and implicates portal hypertension for the rise in fetal GGT with transfusion.

Vibroacoustic stimulation is not associated with sudden fetal catecholamine release.

The safety of vibroacoustic stimulation (VAS), which produces marked changes in fetal heart rate, movements and behavioural state, remains unclear. In order to determine whether VAS is associated with catecholamine release, we measured plasma noradrenaline and adrenaline in 13 appropriately grown normoxaemic fetuses between 28 and 40 weeks gestation immediately before and 60 and 75 s after VAS. Over this time interval, VAS is known to increase fetal heart rate. There was no significant change in either noradrenaline (median change = +0.06 ng/ml, P = 0.26) or adrenaline levels (median change = +0.03 ng/ml, P = 0.4). This study suggests that sympathoadrenal activation is not part of the fetal response to VAS. These findings do not support the recent suggestion that VAS may be deleterious to the fetus by provoking sudden release of catecholamines.

Limited role of fetal blood sampling in prediction of outcome in intrauterine growth retardation.

Fetal acid-base status was evaluated on 66 blood samples taken for rapid karyotyping from 58 growth-retarded fetuses. Before blood sampling, doppler blood flow studies of the umbilical artery showed end-diastolic frequencies to be absent in 32 fetuses (group 1) and present in 26 (group 2). Fetuses with chromosomal (n = 4) or structural (n = 8) abnormalities were excluded from subsequent analysis. Gestational age at blood sampling (27.8 [95% CI 26.5-29.1] vs 32.2 [30.4-34.1] weeks) and time from sampling to delivery (median 2 (range 0-35] vs 14 [0-77] days) were significantly lower in group 1 than group 2. There were no perinatal deaths in group 2 whereas mortality in group 1 was 65.4%. There were significant differences between the groups at blood sampling in pH, pO2, pCO2, base equivalents, and nucleated-red-cell count, but within group 1 these measurements were similar in surviving fetuses and those who died perinatally. Since acid-base determination does not predict perinatal outcome in growth-retarded fetuses, fetal blood sampling has a limited role in monitoring fetal wellbeing.