First-trimester prenatal diagnosis of cystic fibrosis with linked DNA probes

Convergence of Surface-Enhanced Raman Scattering with Molecular Diagnostics: A Perspective on Future Directions

Molecular diagnostics (MD) is widely employed in multiple scientific disciplines, such as oncology, pathogen detection, forensic investigations, and the pharmaceutical industry. Techniques such as polymerase chain reaction (PCR) revolutionized the rapid and accurate identification of nucleic acids (DNA, RNA). More recently, CRISPR and its CRISPR-associated protein (Cas) have been a ground-breaking discovery that is the latest revolution in molecular biology, including MD. Surface-enhanced Raman scattering (SERS) is a very attractive alternative to fluorescence as the currently most widely used optical readout in MD. In this Perspective, milestones in the development of MD, SERS-PCR, and next-generation approaches to MD, such as Specific High-Sensitivity Enzymatic Reporter UnLOCKing (SHERLOCK) and DNA Endonuclease-Targeted CRISPR Trans Reporter (DETECTR), are briefly summarized. Our perspective on the future convergence of SERS with MD is focused on SERS-based CRISPR/Cas (SERS-CRISPR) since we anticipate many promising applications in this rapidly emerging field. We predict that major future developments will exploit the advantages of real-time monitoring with the superior brightness, photostability, and spectral multiplexing potential of SERS nanotags in an automated workflow for rapid assays under isothermal, amplification-free conditions.

Pharmacogenetics of cystic fibrosis treatment

Cystic fibrosis (CF) is genetic autosomal recessive disease caused by reduced or absent function of CFTR protein. Treatments for patients with CF have primarily focused on the downstream end-organ consequences of defective CFTR. Since the discovery of the CFTR gene that causes CF in 1989 there have been tremendous advances in our understanding of the genetics and pathophysiology of CF. This has recently led to the development of new CFTR mutation-specific targeted therapies for select patients with CF. This review will discuss the characteristics of the CFTR gene, the CFTR mutations that cause CF and the new mutation specific pharmacological treatments including gene therapy that are contributing to the dawning of a new era in cystic fibrosis care.

Prenatal diagnosis of cystic fibrosis: the 18-year experience of Brittany (western France)

OBJECTIVE

This study reports 18 years of experience in prenatal diagnosis (PD) of cystic fibrosis (CF) in a region where CF is frequent and the uptake of PD is common (Brittany, western France).

METHOD

All PDs made over the period 1989-2006 in women living in Brittany were collected.

RESULTS

We recorded 268 PDs made in 1 in 4 risk couples, plus 22 PDs directly made following the sonographic finding of echogenic bowel. Most of the 268 PDs were done in couples already having CF child(ren) (n = 195, 72.8%). Close to one-fifth followed cascade screening (n = 49, 18.3%), which identified 26 new 1 in 4 risk couples among the relatives of CF patients or of carriers identified through newborn screening (NBS). The remaining PDs were mainly made in couples whose 1 in 4 risk was evidenced following the diagnosis of echogenic bowel in a previous pregnancy (n = 22, 8.2%). Although patients' life expectancy has considerably improved, in our population the great majority of couples chose pregnancy termination when PD indicated that the foetus had CF (95.9%).

CONCLUSION

This study describes the distribution of PDs according to the context in which the 1 in 4 risk was discovered and highlights the real decisions of couples as regards pregnancy termination after a positive PD.

Cystic fibrosis birth rates in Canada: a decreasing trend since the onset of genetic testing

OBJECTIVE

To estimate cystic fibrosis (CF) birth rates in Canada from 1971 to 2000 and to assess the population impact of genetic testing in families with a history of CF, after identification of the CF transmembrane conductance regulator gene in 1989.

STUDY DESIGN

Age-at-diagnosis data were obtained from the Canadian Cystic Fibrosis Foundation Patient Data Registry and Canadian births for the corresponding years from Canadian Vital Statistics. Estimates of the CF birth rate in each year were based on a nonparametric model that allows the birth rate to vary across the years and adjusts for censoring of currently undiagnosed patients.

RESULTS

The overall CF birth rate from 1971-1987 was 1/2714 with no increasing or decreasing trend. Beginning in 1988, 1 year before identification of the CF transmembrane conductance regulator gene, estimated CF birth rates followed a linear decline to an estimated rate of 1/3608 in 2000. CF birth rates may have stabilized in the last few years, but further decline may occur with implementation of carrier screening in the general population.

CONCLUSIONS

These results demonstrate the temporal association of genetic testing and declining CF birth rates in Canada. They may assist in decisions relating to the allocation of resources for prenatal and neonatal CF screening programs.

Prenatal diagnosis of cystic fibrosis: a case of twin pregnancy diagnosis and a review of 5 years' experience

We performed prenatal diagnoses for cystic fibrosis in 32 high risk (1:4) couples (including a dizygotic pregnancy). Chorionic villi sampling did not cause abortion or fetal malformation in any case. The preliminary analysis of 9 short tandem repeats always excluded maternal contamination of the DNA extracted from chorionic villi and confirmed paternity. Twenty-two prenatal diagnoses were made by direct analysis of the mutations. In seven cases diagnosis was made by the analysis of intragenic polymorphisms; in three cases, we analyzed two extragenic polymorphisms. The prenatal diagnosis (including genetic counselling) was completed within 24 h from the sampling. Seven prenatal diagnoses revealed an affected fetus; all couples opted for therapeutic abortion. In 17 cases the fetus was heterozygote, and in seven cases it was non carrier of mutated alleles. In the twin pregnancy, mutations were DeltaF508/N1303K. Direct analysis of the DNA extracted from the two independent samples of chorionic villi revealed one fetus non carrier of mutated alleles and the other a carrier of the N1303K mutation. Analysis of the HPRT locus predicted both the fetuses as males. Furthermore, the genotype of each fetus was defined after birth. The prenatal diagnosis with chorionic villi sampling plays a key role in the prevention of cystic fibrosis. The laboratories must be equipped for both the direct analysis of mutations and for the analysis of a large number of polymorphisms. The preliminary analysis of short tandem repeats is recommended both to exclude maternal contamination and to confirm parentage.

Universal community carrier screening for cystic fibrosis?

Approximately 5% of the Caucasian North European and North American populations are carriers of the gene defect causing cystic fibrosis (CF). Since the CF gene was isolated in 1989 and the common mutations identified, there has been debate as to whether community-wide screening for CF carriers should be offered. Pilot studies and new discussions are leading to a consensus that screening is now possible and will not lead to undue anxiety, but there is still no agreement as to cost, or how it will be used by those screening positive.

A scientific basis for cost-benefit analysis of genetics services

Economic appraisal of genetics services is important, but, in this sensitive area, analyses limited to financial aspects understandably cause public concern. Evaluation of these services must take account of their aim of helping everyone with a genetic disadvantage to live and reproduce as normally as possible, and must apply equally to patients and to couples at risk of having affected children. Here we propose that the classical concept of genetic fitness can be useful in evaluating genetics services, because it is measurable, and truly represents their underlying aim.

Effect of introducing prenatal diagnosis on the reproductive behaviour of families at risk for cystic fibrosis. A cohort study

We studied 101 couples to determine how far their reproductive behaviour was affected by the diagnosis of cystic fibrosis (CF) on its first occurrence in the couple's progeny and by the availability of prenatal diagnosis (PD). The couples were all resident in the Veneto and Trentino regions and attending the Verona CF Centre. CF had been diagnosed in the first affected child, during the period 1 January 1980-1 July 1990, before the age of 1 year. Couples received a questionnaire regarding socio-demographic status, reproduction data, and awareness of PD. Reproductive history was divided into three phases: prior to diagnosis of CF in the first affected child; from this time until PD was made available; and after the couples had learned of PD. In phase 2 (awareness of the genetic risk but not of PD), 54 couples showed a marked decrease in reproduction, none of the few pregnancies that occurred being taken to term. When couples became aware of PD, some resumption of reproductive activity occurred and 11 per cent of the 101 couples had another child; PD was used in 65 per cent of pregnancies and the abortion rate decreased to 35 per cent. All couples who opted for PD had no children without CF.

Nine mutations in the cystic fibrosis (CF) gene account for 80% of the CF chromosomes in French patients

Thirteen mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene have been screened in a French sample of 185 cystic fibrosis (CF) patients, together with their respective associated RFLP haplotypes at the linked D7S23 locus (XV2C and KM19 markers). The respective frequencies of the mutations showed that 9 of them account for 80% of the CF chromosomes. Implications for prenatal diagnosis and heterozygote detection are defined and discussed. The well-known great excess of RFLP B marker within CF chromosomes is partially explained by two already characterized mutations highly associated with haplotype B: delta F508 and G542X. Similarly, the excess of haplotype D within CF chromosomes is partially explained by the association between delta I507 and this haplotype. These results may suggest the existence of two still untested or uncharacterized mutations, whose frequencies could be near 1%, one which would be associated with haplotype B and a second which would be associated with haplotype D. The possible cause of the specific association between most of the main different CF mutations and the RFLP haplotype B is discussed.

A CF-lectin factor in amniotic fluid from pregnancies at risk for cystic fibrosis

A method was developed for the assay of the CF-lectin factor in amniotic fluid using samples from fetuses identified by other means as having or not having cystic fibrosis (CF). The method involves protein removal from the amniotic fluid by filtration through Centricon-10 Amicon filters, admixture of filtrate with normal serum as a source of IgM, and incubation in 5% Dextran-Sulfate with mouse red blood cells to detect specific hemagglutination. Blind samples submitted from four different laboratories were used to evaluate the ability of the assay to differentiate CF fetuses from fetuses without CF. Storage of samples from one laboratory had been quite prolonged and was associated with poor correlations. Freezing and thawing of samples were shown to deactivate the CF-lectin factor. In three of the four studies, CF lectin was detected in 77% of pregnancies identified as CF at birth, prenatally through microvillar enzyme assay or through DNA analysis of terminated pregnancies. Eighty-three percent of samples identified as normal were confirmed as such by a lack of CF-lectin activity. These data suggest that CF fetuses produce, and are exposed to, the CF-lectin factor at least as early as the second trimester of gestation.

Attitudes toward abortion among parents of children with cystic fibrosis

BACKGROUND

DNA prenatal diagnosis for cystic fibrosis (CF) has been available for parents of affected children since late 1985.

METHODS

Using anonymous questionnaires, we surveyed 395 parents of children with CF at 12 New England CF centers with regard to 12 maternal or family situations and 11 fetal characteristics; 271 (68%) responded.

RESULTS

The majority supported legal abortion in the first trimester for all 23 situations; 58% would abort for severe mental retardation (MR), 40% would abort for a genetic disorder leading to death before age five years, 41% for a child bedridden for life, 35% for moderate MR, 20% for CF and 17% for a severe incurable disorder starting at age 40 years. Few would abort for a disorder starting at age 60 years, for genetic susceptibility to alcoholism or for sex selection. Variables most strongly related to abortion for CF were attitudes of spouse, respondent's siblings, and CF doctor toward abortion for CF as well as infrequent attendance at religious services.

CONCLUSIONS

Prenatal diagnosis may not reduce substantially the number of CF births to parents of CF children because most do not accept abortion for CF.

Medical genetics

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Development of a screening system for cystic fibrosis: meconium or blood spot trypsin assay or both?

High blood trypsin levels during early days of life are found in newborns subsequently diagnosed to be affected by cystic fibrosis. The authors compared the validity of the traditional meconium test with the blood immunoreactive trypsin (IRT) assay, carried out in parallel on 113,302 neonates from three regions of North-eastern Italy. The meconium test showed a sensitivity of 57.7%. The sensitivity of the IRT test was higher (96.1%). It was possible to identify by IRT 10 out of 11 false negative CFs at the meconium test. A shortcoming of neonatal IRT, however, is its low specificity; 1.6% of the newborns had to be retested. A new screening policy was therefore proposed and carried out on 69,640 newborns: the Lactase test (LACT) on meconium was introduced as a complementary assay in IRT positive newborns. If LACT exceeded 2 U/g dry meconium, a confirmatory sweat test was immediately requested; if LACT test was negative and IRT exceeded 85 micrograms/l, IRT was repeated. Postneonatal retesting values above 25 micrograms/l required a sweat test. As a result, the estimated prevalence of CF was 1:4,352, the sensitivity was 93.3%; the specificity turned out to be 99.6%, considering all false positive newborns investigated with retesting and/or direct sweat test.

Mutation analysis for heterozygote detection and the prenatal diagnosis of cystic fibrosis

The cystic fibrosis gene was recently cloned, and a three-base deletion removing phenylalanine 508 from the coding region was identified as the mutation on the majority of cystic fibrosis chromosomes. We used the polymerase chain reaction and hybridization with allele-specific oligonucleotides to analyze the presence or absence of this mutation on 439 cystic fibrosis chromosomes and 433 normal chromosomes from non-Ashkenazic white families. This mutation was present on 75.8 percent of the cystic fibrosis chromosomes. Using the DNA markers XV-2c and KM-19, we found that 96 percent of cystic fibrosis chromosomes with the mutation had a single DNA haplotype that occurs frequently with cystic fibrosis chromosomes. This haplotype was also found on 54 percent of the cystic fibrosis chromosomes without the three-base deletion. The three-base deletion was found on only 30.3 percent of cystic fibrosis chromosomes from Ashkenazic families, although the common cystic fibrosis haplotype was present on 97 percent of cystic fibrosis chromosomes from Ashkenazic families. The ability to detect the common mutation causing cystic fibrosis represents a major improvement in prenatal diagnosis and heterozygote detection, particularly in families in which no DNA sample is available from the affected child, and provides an improved method of testing for spouses of carriers of cystic fibrosis. Mutation analysis introduces the possibility of population-based screening programs for carriers, which on the basis of the sample in this study, would currently identify about 57 percent of the non-Ashkenazic white couples at risk.

The genotype of a new linked DNA marker, MP6d-9, is related to the clinical course of cystic fibrosis

The clinical symptoms of a cohort of cystic fibrosis patients were related to their genotypes using RFLPs shown with MspI and the closely linked DNA marker MP6d-9. In the majority of CF chromosomes, the restriction site for MspI was present, and the genotype 2/2 was found most often in patients who were severely affected by the disease. The genotype 1/2 was significantly over-represented in patients with very mild clinical manifestations, including pancreatic sufficiency, absence of meconium ileus, and absence of Pseudomonas colonisation. When pancreatic dysfunction was present, the 1/2 genotype was associated with a mild form, while the 2/2 genotype was found in patients with severe insufficiency. None of our patients had the 1/1 genotype. These results indicate that the newly isolated MP6d-9 marker correlates with some important symptoms of cystic fibrosis.

Prenatal diagnosis of cystic fibrosis by using linked DNA markers in 138 pregnancies at 1-in-4 risk

Prenatal diagnosis was carried out in 138 pregnancies at 1-in-4 risk for cystic fibrosis (CF) by using closely linked DNA markers, including XV-2c and KM-19. In fully informative families, 25 of 123 (20%) fetuses were predicted to be affected; 16 of these 25 pregnancies were terminated and 9 were continued. Postnatal sweat tests are completed in 42 cases; the diagnoses were confirmed in 4 of 4 infants predicted to be affected and in 37 of 38 infants predicted to be unaffected. One infant predicted to be a carrier had an abnormal sweat test after birth, but the mother also had an abnormal sweat test, and there was no evidence of an error in linkage analysis. The data indicate that prenatal diagnosis using linkage analysis is fully informative in most families and is highly reliable with either chorionic villus sampling or amniocentesis. Although outcome data are available on only 42 pregnancies, based on our experience, on general principles of linkage analysis, and on the tight linkage of the known DNA markers with CF, we recommend that DNA analysis replace microvillar intestinal enzyme analysis for 1-in-4 risk pregnancies when DNA is available from the propositus.

First-trimester prenatal diagnosis of cystic fibrosis using the polymerase chain reaction: report of eight cases

Eight pregnancies at risk for cystic fibrosis have been monitored by first-trimester prenatal diagnosis with DNA amplification analysis. The polymerase chain reaction (PCR) was used in all cases to amplify the region detected by KM19. In two cases, the region detected by CS.7, another DNA probe tightly linked to the CF locus, was also examined. The results of the PCR determinations were confirmed using the Southern blotting procedure, by segregation analysis of restriction fragment length polymorphisms (RFLPs) relative to XV-2c, J3.11, metH, metD, and KM19 probes.

Molecular genetics in the National Health Service in Britain

A recent report from the Departments of Health draws attention to the value of DNA diagnosis for inherited diseases and the need for planning these services in the National Health Service. There is great potential for preventive medicine, but a major immediate benefit is the newfound ability to exclude the carrier state in many people at risk and to protect fetuses from abortion when, as in most cases, they are shown to be normal by DNA tests. However, the widespread application of these new techniques requires prior evaluation and general acceptance. This will only be obtained after public debate, education of professionals and the population, and the establishment of adequate non-directive genetic counselling services. Some of the points to be considered in setting up molecular genetics laboratories are described.

Usefulness of linkage disequilibrium of KM-19 and XV-2c DNA probes for genetic counselling in a high-risk CF family

A French couple with an individual risk of carrying the cystic fibrosis (CF) mutation of 1/2 sought genetic counselling. From the DNA haplotypes generated by XV-2c and KM-19 RFLPs, it could be deduced that only one subject was a carrier, lowering the risk of having a CF baby from 1/16 to 1/200. The strong linkage disequilibrium between these RFLPs and the CF allele observed in France reduced the risk to 1/1600.

Diagnosis of genetic disorders at the DNA level

In the past 10 years considerable progress has been made in the diagnosis of hereditary disorders at the DNA level. Many monogenic disorders can now be examined at the gene level; such examination has led to a better understanding of the molecular basis of these disorders and made carrier detection and prenatal diagnosis possible. Each year, more and more monogenic disorders can be added to the list of diseases that can be diagnosed by DNA analysis. Future research will be devoted to the identification of genes responsible for other known monogenic hereditary disorders, the elucidation of the molecular lesion associated with chromosomal abnormalities, and the characterization of the genes and gene defects involved in the common multifactorial diseases. The goal of diagnosis is the identification of the genetic defect in affected patients, persons destined to be affected, and carriers.

Cystic fibrosis: typing 89 German families with linked DNA probes

Three hundred and ninety-two subjects from 89 German families were typed for restriction fragment length polymorphisms (RFLPs) detected by the probes pmetH, pmetD, pJ3.11, KM19, and XV2c known to be tightly linked to the cystic fibrosis (CF) gene. The analysis of the predictive value of this typing in individual CF families indicates that the combined use of these probes provides a powerful diagnostic system for both carrier detection and prenatal diagnosis. In 45 families the complete haplotype including all RFLPs was available. Of them 41 (91.1%) were fully informative and 4 were partly informative.

Prenatal diagnosis of cystic fibrosis using linked DNA probes

This paper presents data collected in Europe on 107 prenatal diagnoses of cystic fibrosis (CF) using linked DNA markers. To date, 38 children have been born without CF, as predicted, demonstrating the present rapid move from research to clinical genetic service.

First-trimester prenatal diagnosis of cystic fibrosis using fibroblasts from a deceased index child to establish haplotypes

First-trimester prenatal diagnosis of cystic fibrosis (CF) using linked DNA markers is usually only possible if there is an index affected child to establish the haplotype of the parental chromosomes. We describe a prenatal diagnosis where fibroblasts, cultured from the skin of a deceased affected child and then held in frozen storage for 3 years, were used as the starting point for tracking the CF gene. The fetus was diagnosed as a homozygous normal and the diagnosis confirmed by immunoreactive trypsin testing after birth. It was also possible to establish heterozygosity in the aunt of the affected child.

Genetic markers on chromosome 7

Chromosome 7 is frequently associated with chromosome aberrations, rearrangements, and deletions. It also contains many important genes, gene families, and disease loci. This brief review attempts to summarise these and other interesting aspects of chromosome 7. With the rapid accumulation of cloned genes and polymorphic DNA fragments, this chromosome has become an excellent substrate for molecular genetic studies.

Prenatal diagnostic options in cystic fibrosis

There are currently two diagnostic options in cystic fibrosis. These involve assays for certain microvillar enzyme activities in amniotic fluid and recombinant deoxyribonucleic acid studies of markers linked to the cystic fibrosis gene on chromosome 7. The former are reduced in cystic fibrosis homozygotes; the latter make it possible to determine the particular pattern of chromosome 7 markers predictive of a cystic fibrosis homozygote in a specific family. However, neither test is appropriate for, applicable to, or informative in all families. The problems and potential of each approach are discussed.

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.

Confirmation of prenatal diagnosis of cystic fibrosis by DNA typing of fetal tissues

Tissues from eight fetuses, diagnosed on the basis of amniotic fluid microvillar enzyme assay as having cystic fibrosis, were conserved in frozen storage for up to three years. Adequate samples of undegraded DNA could be extracted from small intestine, lung, and liver. DNA typing, with restriction fragment length polymorphisms tightly linked to the cystic fibrosis gene, showed all eight diagnoses to have been correct. Determining the DNA genotype of fetal material can also be used to establish the linkage relationship between markers and the cystic fibrosis gene, and will permit subsequent first trimester prenatal diagnosis for couples who have no living affected child.

Carrier prediction of cystic fibrosis in 36 families by means of restriction fragment length polymorphism

Transmission of cystic fibrosis (CF) was studied in 36 families with at least one affected and one unaffected child. DNA was prepared from peripheral leukocytes and submitted to restriction fragment length polymorphism (RFLP) analysis with two CF probes (pj3.11 and met). Twenty families were shown to be informative so that accurate predictions could be made of the status of the offspring. Sixteen were only partially informative. The allele frequency was similar to that originally reported except for one Msp I site detected with the pj3.11 probe, for which we found a significantly higher heterozygote frequency, making it more informative than expected in our population sample. Pedigree analysis demonstrated no obligate recombinant between CF and the polymorphic markers.

Recent advances in cystic fibrosis

Cystic fibrosis, one of the most common lethal inherited disorders in N. European and N. American populations, is characterized by the production of abnormally viscous mucous secretions in the lungs and digestive tract. The pathophysiological basis of the disease is unknown. However, during the last few years, rapid advances in molecular genetics and biochemical and physiological studies on cystic fibrosis epithelial cells have led to optimism that the cystic fibrosis defect will soon be identified. Current evidence suggests that the basic disturbance lies in altered regulation of protein secretion and electrolyte transport leading to an imbalance in composition of epithelial secretions in cystic fibrosis patients. Increasing knowledge of the mechanisms regulating production and secretion of mucins and movement of electrolytes across the cell membrane should lead to development of pharmacological manipulation(s) to correct the cellular abnormality. Ultimately, it is hoped that this will lead to the development of a rational treatment for cystic fibrosis patients.

Genotyping of cystic fibrosis families with linked DNA probes

Forty-six British families, containing at least one child affected with cystic fibrosis, were typed for restriction fragment length polymorphisms (RFLPs) by the probes pmet H, pmet D, pJ3.11 and 7c22. Thirty-five (76%) were fully informative for prenatal diagnosis and carrier detection, while in the remainder prenatal exclusion of an affected fetus could be carried out in half the pregnancies. The frequencies of individual alleles did not differ between cystic fibrosis and normal chromosomes. However, the previously noted excess of one haplotype on chromosomes carrying the cystic fibrosis gene was confirmed.

Pathological confirmation of cystic fibrosis in the fetus following prenatal diagnosis

Prenatal diagnosis of cystic fibrosis is presently based on the determination of microvillar enzyme activities in the amniotic fluid. However, there seems to be no accurate means for confirming the diagnosis of the aborted fetus. During the past year we performed pathological and histopathological examinations on 7 fetuses diagnosed in the second trimester of pregnancy to be affected by cystic fibrosis and compared them with 4 control age-matched fetuses. Glycol-methacrylate-embedded 2-3-mu thick sections of the pancreas, lungs, bronchial tree, and GI tract were stained with toluidine blue, H&E, PAS, and AB-PAS, and examined microscopically. In the controls, PAS-positive granules were dispersed throughout the cytoplasm of most pancreatic acinar and tracheal submucosal glandular cells. In the affected fetuses 2 distinct groups were identified. In one group of 4 fetuses, the pancreatic and tracheal submucosal glands were dilated and contained a weak PAS-positive material. The glandular epithelial cells had very little PAS-positive granules. In this group, the tracheal epithelium was either atrophic or metaplastic and devoid of microvilli. In the second group of 3 fetuses there was less dilation of the glands, and both pancreatic acinar cells and tracheal submucosal glandular epithelial cells contained few PAS-positive granules, which were confined mainly to a perinuclear location. The tracheal epithelial cells contained few microvilli which, when present, appeared thicker and shorter as compared to controls. We feel that histochemical evaluation of pancreatic and bronchial tissue may be of help in the pathological confirmation of cystic fibrosis in human fetuses where the results of the biochemical studies are suggestive of the disease.

Clinic experience of prenatal diagnosis of cystic fibrosis by use of linked DNA probes

96 families at risk of having a child with cystic fibrosis have been counselled about prenatal diagnosis by the use of linked DNA probes. Of the first 30 pregnancies 9 children have been born and confirmed to be free from CF, as predicted; 8 pregnancies were terminated (1 of these was found to be miscarrying at time of termination); 12 pregnancies, in which the fetuses are predicted to be unaffected, are in progress; and 1 has miscarried. No couple with a prenatal prediction of CF decided to continue with the pregnancy. 1 pregnancy was terminated because of a 50:50 chance of an affected fetus. In 1 twin pregnancy the affected fetus was selectively aborted, and the other baby was confirmed after birth to be unaffected, as predicted. In the other twin pregnancy the two chorionic plates could not be samples separately; the pregnancy was continued on the basis of normal findings for the lower plate, and both twins have turned out to be normal. Many couples at risk see early prenatal diagnosis as a way to help them have an unaffected child.

Three additional DNA polymorphisms in the met gene and D7S8 locus: use in prenatal diagnosis of cystic fibrosis

We have used cloned DNA sequences from the 5' end of the met locus and the D7S8 locus to locate new restriction fragment length polymorphisms. TaqI and MspI polymorphisms with frequencies of 0.34/0.66 and 0.10/0.90, respectively, for met and a PvuII polymorphism (0.15/0.85) at D7S8 are described. We used these new markers to analyze our reference panel of cystic fibrosis pedigrees and found that they provided additional information in several families. No evidence for recombination was observed between the 5' end of met and previously described met markers. We present examples of the use of the met markers in the clinical diagnosis of cystic fibrosis and summarize our analysis of 29 clinical cases including eight prenatal diagnoses. We conclude that DNA-based prediction of cystic fibrosis is an effective clinical diagnostic procedure.

Effect of screening for cystic fibrosis on the influence of genetic counseling

We studied the influence of genetic counseling for cystic fibrosis on family planning, using neonatal screening, family size at time of diagnosis, and maternal age as possible determinants for reproductive behaviour. The expected number of children born to mothers of equal age and parity in the same period was approximated on the basis of population statistics. These numbers were compared to the numbers of children born in the study group after a CF diagnosis and information on the 25% recurrence risk were given. A 50.8% reduction in childbirth was found in the study group, although 77% of families had decided against further high-risk pregnancies. No statistically significant influence of neonatal screening could be demonstrated, but this may be due to the small number of families involved.

Impact of molecular biology on clinical genetics

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Fetal diagnosis of inborn errors of metabolism

Nearly 4000 different human disorders are supposed or known to be due to a single gene mutation. In about 10%, an early diagnosis is possible by the demonstration of specific abnormalities of metabolites in blood and/or urine, an abnormal structure/function of a particular (enzyme) protein or by the (in)direct demonstration of the gene mutation using DNA analysis. These methods of molecular analysis can often also be used for carrier detection. Early identification of couples at risk of handicapped offspring followed by genetic counselling forms the basis for prevention. Follow-up studies have shown that more than half of the couples at risk of a child with a genetic disease refrain from pregnancy. An important alternative for couples at risk is prenatal monitoring and selective abortion. During the last 10-15 years, the technology of fetal diagnosis of genetic diseases has improved and the number of Mendelian disorders that can be diagnosed in utero has increased to more than 100. In the second-trimester of pregnancy, about two dozen inborn errors of metabolism have been diagnosed by metabolite analysis of amniotic fluid supernatant using gas chromatography-mass spectrometry or electrophoretic methods. About 5000 pregnancies at risk of different types of haemoglobinopathy, haemophilia, alpha-1-antitrypsin deficiency and a few other diseases not expressed in amniotic fluid cells have been investigated by biochemical analysis after fetal blood sampling. The most common approach towards fetal diagnosis of inborn errors of metabolism has been the demonstration of a specific enzyme deficiency in cultured amniotic fluid cells. In this way some 60 different diseases have been diagnosed, usually after 2-4 weeks of cultivation after amniocentesis at 16 weeks gestation. In addition, some 20 other Mendelian disorders have been diagnosed in utero by ultrasonography and non-biochemical analysis of amniotic fluid cells or fetal skin biopsies. The introduction of chorionic villus sampling has offered the possibility of first-trimester fetal diagnosis of a large number of Mendelian disorders. The overall diagnostic experience until mid-1986 amounts to about 1500 pregnancies at risk. Some 45 different inborn errors have been diagnosed by enzyme assays directly on chorionic villus homogenate or after incubation with radiolabelled precursors of intact villi followed by chromatography or other types of analysis. In a few instances, cell cultivation for a period of 2-3 weeks is required to establish a reliable biochemical diagnosis.

Diagnosis of genetic disease using recombinant DNA. Supplement

Recombinant DNA methodology has greatly increased our knowledge of the molecular pathology of the human genome at the same time as providing the means to diagnose inherited disease as the DNA level. We present here a list of recent reports of both direct and indirect analysis of human inherited disease which is intended to serve as a guide to current molecular genetic approaches to diagnostic medicine.

Fetal diagnosis of cystic fibrosis

Two different methods of prenatal diagnosis of CF are currently available. Both are usually only suitable for couples with a 1 in 4 risk of bearing an affected child. The method of choice is first trimester diagnosis on a chorionic villus sample using linked DNA probes. The advantages are: 1. The very high degree of accuracy of diagnosis, 2. The opportunity of first trimester termination of pregnancy when the fetus is affected. The disadvantages are: 1. The need for a blood sample from an index affected child to establish phase, 2. The requirement for early workup of the nuclear family to ascertain informativeness, 3. The chance that some families will be uninformative or only partially informative for available DNA probes. An alternative form of diagnosis is that using microvillar enzyme testing on second trimester amniocentesis samples. The advantages are: 1. It is suitable for all pregnancies with a 1 in 4 risk of CF, 2. No prior workup of the family is required, 3. Assays can be completed within one hour of receipt of the sample. The disadvantages are: 1. The accuracy of diagnosis leaves some scope for error, 2. If termination of pregnancy is indicated this can only be carried out at about 18 or 19 weeks of gestation.

The management of the patient having fetal diagnosis

The non-technical aspects of delivery of prenatal diagnostic services deserve consideration. Communication with the patient and her partner about their risks of fetal abnormality, the risks of tests and the interpretation of results is essential if the couple are to make the right choices for themselves. Some results of prenatal tests are easy to interpret but others are more difficult either because the clinical consequences cannot be predicted or because the laboratory results are 'borderline' or could be artifactual. Further tests to clarify the situation may be necessary and expert help sought from several disciplines. Staff involved in the care of a woman undergoing termination of pregnancy should be willing to participate in the procedures sympathetically. Post-termination examination of the aborted fetus is necessary both for genetic counselling and quality control for the tests employed. Throughout the various stages of prenatal diagnosis, support should be provided for the couple; this is particularly necessary for those who have had a previous abnormal baby. For those undergoing termination of pregnancy, skilled help should be offered to minimize long-term adverse sequelae.