Predictive testing for Huntington disease: social characteristics and knowledge of applicants, attitudes to the test procedure and decisions made after testing

An investigation has been made of the social characteristics and knowledge and experience of Huntington disease (HD) for the first 80 individuals considering presymptomatic testing (applicants) at the medical genetics centres in Edinburgh and Glasgow and of attitudes to the test procedure and decisions made after testing for those who received a result. Sixty-one percent of applicants were female and 31% were over 40 years old. Almost all had a symptomatic parent but 38% did not know HD was in their family until they were over 25 years old and 48% had never received genetic counselling. Thirty-eight percent of applicants first heard of the test at the genetic clinic, 20% from a relative and 20% from the media, but none had received information from their GP. Thirty-one applicants did not have the test because they voluntarily withdrew (17 individuals), their family structure was unsuitable or no informative result was possible (11 individuals), or they were diagnosed clinically as being affected (3 individuals). Those who voluntarily withdrew did not differ significantly from the 49 who received a result in social characteristics or knowledge and experience of HD. Twenty-two individuals were found to be at increased risk (IR) (> 50% of becoming affected) and 27 to be at decreased risk (DR) (< 50% of becoming affected). There was a median period of 9 months between entering the test procedure and receiving a result and the main criticism of the procedure was that it took too long to complete and several individuals experienced considerable anxiety while awaiting their result.(ABSTRACT TRUNCATED AT 250 WORDS)

Antenatal detection of neural tube defects: comparison of biochemical and immunofluorescence methods

The aim of this study was to determine whether identification of glial cells in amniotic fluid samples could form a useful supplementary test in the antenatal diagnosis of neural tube defects (NTDs). In a 5-year study, 1452 samples of middle trimester amniotic fluid were examined blind to the results of other antenatal diagnostic tests and to the outcome of pregnancy. Reason of amniocentesis included raised serum alpha-fetoprotein (329), previous NTD (73), and a family history of NTDs (71). Duplicate cytospin preparations were stained with Giemsa and an antibody to glial fibrillary acidic protein (GFAP), and on this basis a prediction of fetal NTD status was made which was not communicated to clinicians. Subsequent management of pregnancies was influenced only by the results of routine antenatal testing for NTDs. Twenty cases of NTDs occurred among the 1406 cases in which the outcome was subsequently known. Of these 20 cases, only five (four anencephalic, one spina bifida) were correctly predicated by immunofluorescent identification of GFAP-positive cells in the amniotic fluid. The remaining 15 cases (two anencephalic, 13 spina bifida) were not so identified. In a further 18 cases, apparently GFAP-positive cells were identified in the absence of NTDs. We conclude that GFAP immunofluorescence examination of routine amniocentesis samples of amniotic fluid is not a useful predictive test for NTDs.

Linkage disequilibrium and recombination make a telomeric site for the Huntington's disease gene unlikely

In a Scottish family in which Huntington's disease (HD) was segregating, recombination was observed between the D4S115/S111 and D4S43/S95 loci, with the HD gene associated with the more proximal D4S43/S95 locus. Analysis of linkage disequilibrium in Scottish families showed significant non-random association between the HD gene and alleles at the D4S95 and D4S98 loci. This adds to previous evidence that the HD locus is not sited at the telomere of chromosome 4.

First-trimester prenatal diagnosis of hypophosphatasia: experience with 16 cases

We have carried out first-trimester prenatal diagnosis of hypophosphatasia in 16 pregnancies with a 1 in 4 risk of this condition. The liver/bone/kidney isoenzyme of alkaline phosphatase was measured in chorionic villus samples using a specific monoclonal antibody and an enzymatic amplification system. Fifteen of the 16 pregnancies were correctly predicted, while one has been lost to follow up. We suggest that this assay system is likely to be superior to DNA-base methods for the first-trimester prenatal diagnosis of hypophosphatasia.

First-trimester maternal serum biochemical indicators in Down syndrome

A set of 21 early maternal serum samples (19 first-trimester and two at 14 weeks) from pregnancies resulting in a child with Down syndrome was matched for gestation and length of storage with 63 samples from unaffected pregnancies. The concentrations of alpha-fetoprotein (AFP), unconjugated oestriol (uE3), human chorionic gonadotrophin (hCG), pregnancy-specific beta 1-glycoprotein (SP1), and placental alkaline phosphatase (PALP) were measured. The ratios of the medians for Down syndrome pregnancies compared with the medians for controls were AFP 0.71, uE3 0.67, hCG 1.43, SP1 0.79, and PALP 0.92. Although the differences between the medians for affected and unaffected pregnancies were not significant, the trends for AFP, uE3, and hCG confirm earlier findings on first-trimester samples.

Predictive testing for Huntington's disease with linked DNA markers

Availability of new DNA markers, more tightly linked to the Huntington's disease (HD) locus than the original G8 (D4S10) probes, has improved predictive accuracy for both presymptomatic and prenatal exclusion testing. 50 predictive tests were carried out on high-risk individuals. 6 of these were on first-trimester chorionic villus biopsy specimens; in 2 cases the HD gene was not transmitted to the fetus while in 4 cases no exclusion could be made. The remaining 44 tests were on adults with either 25 or 50% risk of manifesting the disease; 19 had a greatly increased risk and 25 a substantially decreased risk of HD. Family structures in Scotland are suitable for testing about 75% of potentially affected individuals, and the new generation of DNA markers makes virtually all families fully informative.

Prospective prenatal screening for fetal abnormalities using a quantitative immunoassay for acetylcholinesterase

An immunoassay based on a monoclonal antibody specific for acetylcholinesterase (AChE) was used prospectively over a two year period to screen second trimester amniotic fluids for fetal abnormalities. All 26 cases of spina bifida, three of which had normal alphafetoprotein (AFP) concentrations and ultrasound scans, were detected by the immunoassay. Four clear fluids, with abnormal AFP concentrations, had normal AChE titres and yielded normal outcomes. Some difficulties were encountered with both the AChE immunoassay and polyacrylamide gel testing when amniotic fluids were contaminated with old blood. However, the quantitative nature of the AChE immunoassay and its independence of operator experience make it an ideal adjunct to AFP assay for routine screening of amniotic fluids.

Prenatal diagnosis of cystic fibrosis by microvillar enzyme assay on a sequence of 258 pregnancies

Prenatal diagnosis of cystic fibrosis by microvillar enzyme assay on amniotic fluid supernatant has been carried out on 258 sequential pregnancies with a 1 in 4 recurrence risk, all with known outcome. In general the three enzymes evaluated, gamma-glutamyltranspeptidase, aminopeptidase M and the intestinal isoenzyme of alkaline phosphatase, showed a high degree of concordance. However, there were two unusual patterns of microvillar enzyme activity; in seven cases a low gamma-glutamyltranspeptidase activity was associated with elevated values of intestinal alkaline phosphatase, and in ten cases there were isolated low values of intestinal alkaline phosphatase. The former pattern was found to be associated with cystic fibrosis in five cases, while the latter was associated with a normal outcome in all ten cases. A retrospective analysis of enzyme values suggested that the optimal system for minimizing false positives and false negatives was to define foetal cystic fibrosis as a sample where two of the three microvillar enzymes were below a cut-off of half the median value for the gestational week. If such scoring were applied to the cases where conventional microvillar enzyme patterns were observed, the false positive rate was 2.3% and the false negative rate 4.4% between 17 and 20 weeks of gestation.

Measurement of placental alkaline phosphatase in maternal plasma as an indicator of subsequent low birthweight outcome

Placental alkaline phosphatase (P-ALP) was measured by a specific monoclonal antibody-based immunoassay in plasma samples of 117 women who subsequently were delivered of an infant of birthweight less than 2.5 kg. P-ALP values greater than twice the normal median were found in 32% of maternal plasma samples from low birthweight cases in one series and in 35% in another series, while in normal outcome controls the corresponding value was 8%. The differences were highly significant. The proportion of low birthweight cases with elevated maternal P-ALP values appears to be very similar between 15 and 34 weeks gestation. At 16-18 weeks gestation there is a significant positive correlation (r = 0.40) between P-ALP and maternal plasma alpha-fetoprotein (AFP) values in low birthweight cases. The use of P-ALP assay in combination with AFP assay appears to improve the detection of pregnancies with subsequent low birthweight outcome.

Biochemical analysis of meconium in fetuses presumed to have cystic fibrosis

A series of proteins (albumin, transferrin, alpha 1-antitrypsin, alpha-fetoprotein and pancreatic oncofetal antigen) and enzymes (gamma-glutamyltranspeptidase, aminopeptidase M, alkaline phosphatase, alpha-glucosidase and protease) was measured in fetal meconium extracts. There were 19 fetuses thought to have cystic fibrosis (CF), 13 with neural tube defects, three with chromosome abnormalities and 19 normal controls, all with gestational ages between 18 and 21 weeks. With the exception of alpha-fetoprotein, all the proteins and enzymes were significantly elevated in the CF meconium extracts. The most definitive indicator of a CF fetus was the albumin concentration, where the mean level was five times that found in the control groups. However, five of 19 fetuses assumed to have CF had albumin in the normal range. In these cases the meconium protease levels were grossly elevated. Furthermore, in the same five fetuses meconium concentration of pancreatic oncofetal antigen, a protein synthesized in the fetal pancreas, was also greatly raised. We suggest that post-mortem examination of a fetus thought to have CF should include measurement of meconium albumin, protease and pancreatic oncofetal antigen.

A monoclonal antibody assay technique for plasma and red cell acetylcholinesterase activity in Alzheimer's disease

Acetylcholinesterases (AChE) in human plasma and red cells have been considered as possible markers for Alzheimer's disease. Findings however vary widely and no significant pattern has emerged. The present study has used a new technique for AChE assay based on a monoclonal antibody raised against red cell AChE. This allows AChE isoenzymes to be measured directly in the presence of non-specific cholinesterases without the need for inhibitors. AChE activity in plasma and red cells was assayed in Alzheimer's disease, multi-infarct dementia, Huntington's and alcoholic Korsakoff syndrome, and the results compared both between groups and with normal controls. No significant differences in either red cell or plasma enzyme activity were found by any of these comparisons. Our findings do not suggest that in the dementias peripheral AChE activity reflects altered central cholinergic function, nor that it is likely to prove a useful marker for Alzheimer's disease.

First trimester diagnosis of hypophosphatasia with a monoclonal antibody to the liver/bone/kidney isoenzyme of alkaline phosphatase

Prenatal diagnosis of hypophosphatasia was made by alkaline phosphatase (ALP) assay on a chorionic villus sample taken in the first trimester. Monoclonal antibodies against the liver/bone/kidney (LBK) and placental isoenzymes of ALP were used, and the bound isoenzymes were quantified by an amplification system. Very low activities of the LBK isoenzyme indicated an affected fetus. Diagnosis was confirmed by ultrasound scan at 15 weeks' gestation, and by ALP measurement in amniotic fluid supernatant and fetal serum.

Distinguishing hygroma and amniotic fluid

Fluid from cystic hygromata can be distinguished from amniotic fluid by measurement of alkaline phosphatase (ALP) isoenzymes. The former has a serum-type ALP, made up largely of the liver/bone/kidney isoenzyme and virtually no intestinal isoenzyme. Second trimester amniotic fluid ALP contains approximately 80 per cent intestinal isoenzyme.

Prospective prenatal diagnosis of cystic fibrosis

An immunoassay based on monoclonal antibodies with specificity for the three major isoenzymes of alkaline phosphatase (ALP) has been used in second-trimester prenatal diagnosis of cystic fibrosis (CF). 140 pregnancies with a 1-in-4 risk of CF were assessed prospectively, and outcomes are reported for 100 of these. In 9 cases the diagnosis could not be confirmed or excluded, in 65 cases the infant was normal, and in 15 the infant had CF. In the remaining 11 cases, in which the pregnancy was terminated, the diagnosis of CF was confirmed in the abortus by measurement of albumin and protease levels in meconium scraped from the fetal ileum. Of the 26 cases of CF in the prospective series, 23 (88%) had values of intestinal ALP below half the median value for the corresponding week of gestation. Among those with normal outcomes 3 of 65 (4.6%) were below half-median. When prospective and retrospective data are summed the sensitivity of the test was 91% (39 of 43) and the false-positive rate 6% (5 of 81). This is probably an acceptable form of prenatal diagnosis of CF for the high-risk mother.

Prenatal diagnosis of neural-tube defects with a monoclonal antibody specific for acetylcholinesterase

An immunoassay for acetylcholinesterase (AChE), based on a monoclonal antibody (AE-2), gave the following results when applied to a panel of amniotic fluids: (a) among 651 samples with normal outcome and normal alphafetoprotein (AFP) values there were 2 (0.31%) false positives; (b) of 9 samples with normal outcome and raised AFP values 1 had a raised AChE titre; (c) all 48 samples from anencephaly cases had raised AChE values; (d) among 49 samples from open spina bifida cases (2 of which had normal AFP values), 48 had raised AChE titres. It is suggested that a monoclonal-antibody-based immunoassay may displace polyacrylamide gel electrophoretic analysis of AChE as a complementary test to AFP in prenatal diagnosis of neural-tube defects, since it is a quantitative test largely independent of operator skill and experience.

Prenatal diagnosis of cystic fibrosis using a monoclonal antibody specific for intestinal alkaline phosphatase

A monoclonal antibody (AAP-1), specific for the intestinal isoenzyme of alkaline phosphatase (ALP), has been used to develop an immunoassay for amniotic fluid samples. Values in the immunoassay correlated closely with those obtained by direct determination of phenylalanine-inhibitable ALP. A panel of 124 control second-trimester amniotic fluids and 21 fluids with a 1 in 4 risk of a cystic fibrosis fetus were examined in the immunoassay. Eight of 10 affected cases had values below an arbitrary cut-off of one third median, while all the non-affected cases were above this level. Almost identical results were obtained by enzymatic determination of phenylalanine-inhibitable ALP. However, in both systems the false positive rate (control fluids with values below one third median), was unacceptably high. It is pointed out that at present the most effective system for the prenatal diagnosis of cystic fibrosis is achieved by measuring the ratio of intestinal to total ALP in amniotic fluid supernatants. This is probably best effected by enzymatic assay in the presence of phenylalanine and homoarginine inhibition.

A screening assay for monoclonal antibodies based on the availability of a polyclonal antiserum

A double-sandwich enzyme-linked immunospecific assay (ELISA) has been developed for screening hybridoma clones for monoclonal antibodies against human alpha-fetoprotein (AFP). The assay uses commercial polyclonal antiserum to bind alpha-fetoprotein from biological fluids, and the complex then binds the specific monoclonal antibodies in hybridoma culture supernatants. The sandwich is completed with commercial peroxidase-linked anti-mouse immunoglobulin. In exploring the variables of this system, it was found that the quality of the polyclonal anti-alpha-fetoprotein antiserum was the most critical factor. The assay functioned with as little as 10 ng alpha-fetoprotein from cord serum or amniotic fluid. A variety of commercial peroxidase-linked second antibodies was satisfactory, and both IgG and IgA class monoclonals were detected. Comparison of the ELISA with a standard radioimmunoassay showed the former to perform very adequately as a general hybridoma screening assay.

Comparison of activated charcoal and gastric lavage in the prevention of aspirin absorption

Effectiveness of initial treatment of aspirin (ASA) overdosage was evaluated by comparing treatment with activated charcoal (AC) to treatment with gastric lavage in combination with AC. Dogs were used as subjects in four experimental groups. All subjects were administered an overdose of 500 mg/kg of ASA. Treatment was performed 30 minutes later on all groups except controls. Treatment with AC alone resulted in a 17% reduction (P greater than .05) of peak plasma salicylate levels compared with controls. When lavage preceded administration of AC, a 37% reduction (P less than .05) occurred. There was a 48% reduction (P less than .025) in plasma salicylate levels when lavage was preceded and followed by administration of AC. This study demonstrates that gastric lavage in combination with AC is more effective in reducing ASA absorption than AC given alone.

Enzyme-linked immunospecific assays for human alphafetoprotein using monoclonal antibodies

Two sandwich-type enzyme-linked immunospecific assays for human alphafetoprotein (AFP) have been developed. In both assays monoclonal antibodies were immobilised by absorption to the wells of microtitre plates and used to trap AFP in the samples offered. Bound AFP was then quantitated by completing the sandwich with peroxidase-conjugated anti AFP, which was either of polyclonal or monoclonal type. The monoclonal to monoclonal sandwich enable AFP measurements to be made in the range 100 to 1000 kU/l. The polyclonal to monoclonal sandwich covered an AFP range of 10 to 1000 kU/l. Both assays were rapid and robust and extremely sparing in the use of antibody.

Maternal plasma alpha-fetoprotein and low birthweight: a prospective study throughout pregnancy

Maternal plasma alpha-fetoprotein (AFP) was measured serially between 15 weeks gestation and term in 520 patients. Thirty-seven of these women were delivered of normal singleton infants with birthweights less than 2.5 kg. The median plasma AFP values in this group of women were highest between 15 and 20 weeks gestation and then declined steadily towards term. It is concluded that the use of maternal plasma or serum AFP in the early detection of low birthweight babies is optimal in the period most suitable for screening for fetal neural tube defects.