Prenatal diagnosis of medium-chain acyl-CoA dehydrogenase (MCAD) deficiency in a family with a previous fatal case of sudden unexpected death in childhood

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is a potentially fatal inherited disease with a carrier frequency of approximately 1:100 in most Caucasian populations. The disease is implicated in sudden unexpected death in childhood. A prevalent disease-causing point mutation (A985G) in the MCAD gene has been characterized, thus rendering diagnosis easy in the majority of cases. Since the clinical spectrum of MCAD deficiency ranges from death in the first days of life to an asymptomatic life, there are probably other genetic factors—in addition to MCAD mutations—involved in the expression of the disease. Thus, families who have experienced the death of a child from MCAD deficiency might have an increased risk of a seriously affected subsequent child. In such a family we have therefore performed a prenatal diagnosis on a chorionic villus sample by a highly specific and sensitive polymerase chain reaction (PCR) assay for the G985 mutation. The analysis was positive and resulted in abortion. We verified the diagnosis by direct analysis on blood spots and other tissue material from the aborted fetus and from family members.     

Maternal serum inhibin levels in second-trimester down's syndrome pregnancies

Maternal serum inhibin levels were measured in 19 second-trimester pregnancies affected by fetal Down's syndrome and 95 unaffected control pregnancies matched for gestational age. A statistically significant elevation was found in the affected pregnancies compared with the controls (Wilcoxon rank sum test: one-tail P=0·02). The median level in the cases was 1·3 times that in the controls, with 95 per cent confidence limits of 0·9–1·9. Although the inhibin levels were unrelated to those of alpha-fetoprotein and unconjugated oestriol in the same samples, there was a statistically significant correlation with human chorionic gonadotropin. This together with the relatively small elevation in cases suggests that inhibin would be of limited value in maternal serum screening for Down's syndrome.     

Early amniocentesis at 11–14 weeks' gestation for the diagnosis of fetal chromosomal abnormality—a clinical evaluation

Early arnniocentesis between 11 and 14 weeks' gestation was offered to 110 women at risk of a chromosomally abnormal fetus due to maternal age. Four were found to be unsuitable for the procedure, and 106 early amniocenteses were performed. In 102 cases, clear amniotic fluid was obtained with a single tap. There were two dry taps and two bloodstained tapis; sampling was repeated in three of these cases before 15 weeks. In the fourth case, placental biopsy was performed at 16 weeks. Thus, we were able to obtain a satisfactory sample in all but three cases(2.8 percent). Karyotyping of cells harvested from the early amniotic fluid samples was successful in all the 105 cases. Cell culture from the initial samples revealed a normal karyotype in 99 cases, two balanced translocations, two tetraploid karyotypes, and two cases of pseudomosaicism. Of the 105 pregnancies successfully sampled, there have been two losses to date (1–8 per cent). Two further patients presented with premature rupture of membranes, both pregnancies having successful outcomes. Sixty-two babies have delivered to date, with four congenital anomalies. There were no respiratory problems. Twenty-nine pregnancies are continuing without known complications, and details are not yet available on the remaining 12. The results indicate that early arnniocentesis may replace the traditional test at 15–17 weeks.     

Estimating the risk of a fetal autosomal trisomy at mid-trimester using maternal serum alpha fetoprotein and age: A retrospective study of 142 pregnancies

Risks appropriate for mid-trimester prenatal screening for autosomal trisomies have been estimated from a combination of maternal age and maternal serum (MS) alpha-fetoprotein (AFP) levels at 16–20 weeks gestation. Published data on the frequency of Down's syndrome births relative to maternal age were modified to include the additional age-related frequency of trisomy 18 and trisomy 13 cases to provide an overall risk for an autosomal trisomy at midtrimester. MSAFP results from a retrospective study of 142 affected (114 trisomy 21, 19 trisomy 18, and 9 trisomy 13)and 113 000 unaffected pregnancies were converted to multiples of the appropriate gestational median (MOM). The AFP levels in the autosomal trisomy pregnancies were found to be significantly reduced at 0.72 MOM of the unaffected pregnancies. Risks (likelihood ratios) were derived from the overlapping log Gaussian distributions for affected and unaffected pregnancies and combined with maternal age risks to give the overall odds of an affected pregnancy. A mid-trimester cut-off risk of 1:280 gave an estimated 37 per cent detection rate for autosomal trisomies in the west of Scotland population for a follow-up (false-positive) rate of 6.6 per cent. These figures compare with a 30 per cent detection and 6.7 per cent false-positive rate if age 35 years and over is used as the sole criterion for selection of at-risk pregnancies.