First-trimester fetal screening of cystic fibrosis in low-risk population

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 screening: a fetus with hyperechogenic bowel may be the index case

BACKGROUND

The potential of hyperechogenic fetal bowel to act as a hallmark for prenatal cystic fibrosis screening in the general population is controversial.

METHODS

Our goal was to evaluate the incidence of cystic fibrosis in 209 fetuses with hyperechogenic bowel diagnosed at routine ultrasonography and with no family history of cystic fibrosis. The diagnosis of cystic fibrosis was based on prenatal screening for the eight mutations most frequently observed in France (deltaF508, deltaI507, 1717-1G-->A, G542X, G551D, R553X, W1282X, N1303K) and at postnatal follow up.

RESULTS

The overall incidence of cystic fibrosis was 7/209 (3.3%) which is 84 times the estimated risk of CF in the general population (112500). Of these seven cases, six were diagnosed prenatally based on DNA analysis (deltaF508/deltaF508, n=5; deltaF508/G542X, n=1). One case in which only one mutation had been recognised was diagnosed clinically after birth (deltaF508/unidentified mutation). Of the seven cases, none was diagnosed at 16-19 weeks, four at 16-24 weeks, and three after this. The incidence of heterozygous fetuses (15/209, 7%) was not significantly higher than the 5% expected in the general population. The mutations involved in these heterozygous cases were deltaF508 (n=13), G542X (n=1), and G551D (n=1).

CONCLUSIONS

Screening for cystic fibrosis should be offered to families in which fetal hyperechogenic bowel is diagnosed at routine ultrasonography. This underlines the need to review genetic counselling in this situation where the fetus is the index case for a genetic disease.

Costs, effects, and savings of screening for cystic fibrosis gene carriers

STUDY OBJECTIVE

Evaluating the costs, effects, and savings of several strategies for cystic fibrosis (CF) gene carrier screening.

DESIGN

A general model for evaluating prenatal, preconceptional, school, and neonatal carrier screening was constructed. For prenatal and preconceptional screening, two strategies were evaluated: single entry and double entry two step couple screening. Firstly, the Dutch situation was evaluated prospectively; subsequently the results were generalised to other carrier frequencies.

SETTING

Prospective simulation model.

MAIN RESULTS

Of all screening strategies, neonatal carrier screening gives most carrier couples an informed choice concerning reproduction. If the parents of carrier newborns would not be tested however, prenatal screening detects most carrier couples. Prenatal and single entry preconceptional screening programmes have a favourable cost-savings balance in the Netherlands under a wide range of assumptions. For double entry preconceptional screening and neonatal screening, high enough values of uptake of screening, prenatal diagnosis, and induced abortion are necessary. School carrier screening does not have a favourable cost-savings balance.

CONCLUSIONS

If a CF screening programme is judged to be useful on individual and social grounds, costs considerations are no obstacle for prenatal and single entry preconceptional screening.

Prenatal cystic fibrosis screening in a low-risk population undergoing chorionic villus sampling for fetal karyotyping

Screening for cystic fibrosis (CF) has been offered to pregnant women seeking chorionic villus sampling (CVS) for prenatal chromosomal abnormality investigation. The mutation panel has increased over the years to include 8 mutations and can detect 65% of abnormal CF genes in the Italian population. Testing was offered to a total of 2214 consecutive pregnant women; 45 of them declined screening (take up rate: 98%). In 1055 of the 2169 pregnancies screened, the test was at first done on the fetus, while in the remaining cases both parents were investigated. Among parents 46 carriers were identified (2.1%), in 41 of whom the mutation was delta F508. In two couples both parents were heterozygous, and in one the fetus was affected and the pregnancy was terminated. Although CF testing offered to pregnant women undergoing invasive investigation such as CVS may not be the model for a mass screening, its very high effectiveness can represent an advantageous component of more comprehensive strategies.

Cystic fibrosis--an Indian perspective on recent advances in diagnosis and management

Cystic fibrosis (CF) is a common inherited disorder in caucasians. The estimated incidence of CF in Asians varies from 1:10,000 to 1:12,000. Indian data is restricted to few case reports. The gene for CF is located on the long arm of chromosome 7 at position 7q13. There are more than 300 identified mutations in CF. The basic defect in CF is a mutational change in the gene for chloride conductance channel. Failure of chloride conductance by epithelial cells leads to dehydration of secretions that are too viscid and difficult to clear. The disease is characterized by abnormal secretions in the respiratory, gastrointestinal and reproductive tract and sweat glands. The common clinical manifestations include meconium ileus in neonatal period, recurrent lower respiratory tract infections (pseudomonas pneumonia, bronchiectasis), steatorrhoea, azoospermia, and in late stages hepatobiliary and endocrine pancreatic dysfunctions. The diagnosis of disease is established by clinical criteria and sweat chloride concentration more than 60 mEq/L. Facilities for DNA diagnosis of common CF mutations are now available in India. The treatment of CF includes early diagnosis, daily clearance of respiratory passages, appropriate antibiotic therapy, aerosolised recombinant human DNase and antibiotics, and nutritional supplementation. The latter include changes in diet composition, pancreatic enzyme supplementation and vitamins and trace mineral supplementation. Gene therapy for the pulmonary manifestations is being tried in a number of centres abroad. Other considerations include heart lung transplantation and ameloride inhalation therapy.

Prenatal diagnosis by chorionic villus sampling

Chorionic villus sampling (CVS) retains its great advantage over mid-trimester amniocentesis by producing early results. Moreover, rapid analytical techniques reduce significantly the waiting time between sampling and diagnosis, while recombinant DNA technology and human gene mapping progress amplify enormously the spectrum of the indications. The recent inclusion in the prenatal diagnosis package of screening tests based on DNA analysis for the major genetic diseases (i.e. cystic fibrosis, fragile-X mental retardation syndrome) may efficiently contribute to prevent the genetic disease. The role of CVS in twin pregnancy has been investigated and compared to amniocentesis. Although these techniques are equally safe, CVS should be considered the approach of choice for a number of technical advantage and in relation to selective fetal reduction in discordant twins. Recent reports have substantially contributed on the hypothetical relationship between limb reduction defects (LRDs) and chorion biopsy. The analysis of LRDs among more than 130,000 CVS reported to WHO CVS-Registry has been unable to find out any relationship between sampling and fetal malformations, including LRDs. In conclusion, first trimester CVS should be considered the gold standard procedure for prenatal diagnosis of genetic diseases.

Carrier screening in the community

A number of different models of cystic fibrosis (CF) carrier screening have now been tested in pilot trials. Apart from opportunistic and cascade testing (which are strictly speaking not true forms of screening), the major programmes have been directed either to young adults in primary care or to pregnant women in antenatal clinics. Only in the latter form of screening has sufficient data been collected to allow conclusions to be reached on the optimum mode of delivery. It seems very probable that when CF carrier screening passes into routine service, it will be the antenatal couple model that is used.

Carrier screening for cystic fibrosis

A number of different models of CF carrier screening have now been tested in pilot trials. Apart from opportunistic and cascade testing (which are strictly speaking not true forms of screening), the major programmes have been directed either to young adults in primary care or to pregnant women in antenatal clinics. Only in the latter form of screening has sufficient data been collected to allow conclusions to be reached on the optimum mode of delivery. It seems very probable that when CF carrier screening passes into routine service, it will be the antenatal couple model that is used.