The CFTR 3849+10kbC->T and 2789+5G->A alleles are associated with a mild CF phenotype.

Most cystic fibrosis (CF) transmembrane receptor mutations are rare. The French CF Registry offers an opportunity to study the genotype-phenotype relationship of these rare alleles. Since 1992, 39 CF patients carrying one copy of the 3849+10kbC->T mutation and 88 the 2789+5G->A allele have been seen at least once in a CF care centre. Among them, 16 carrying the 3849+10kbC->T/Delta F508 genotype and 34 with the 2789+5G->A/Delta F508 genotype were seen in 2000. Their age at diagnosis, sweat chloride concentration, anthropometric and lung function results, and clinical aspects were compared with those homozygous for the Delta F508 mutation matched for sex, age and CF care centre. Major differences, most of them statistically significant, in the age at diagnosis, prevalence of pancreatic insufficiency, and other clinical signs, anthropometric and lung function measures were observed between both compound heterozygote groups and their matched Delta F508/Delta F508 groups. The mean sweat chloride concentration was also lower (close to normal values) among 3849+10kbC->T/Delta F508 patients, but not among 2789+5G->A/Delta F508 patients. In conclusion, both mutations studied here are associated with a milder course of cystic fibrosis disease. The 3849+10kbC->T and 2789+5G->A alleles are splice site mutations, leading to abnormal mRNA; however, a small amount of normally spliced transcripts can also be detected. The presence of these small amounts of normal cystic fibrosis transmembrane receptor protein in these cystic fibrosis patients is likely to be responsible for the milder severity of disease and a better life expectancy.

Prevalence of CFTR mutations in hypertrypsinaemia detected through neonatal screening for cystic fibrosis.

Nowadays, most of the neonatal screening programs for cystic fibrosis (CF) combine the assay of immunoreactive trypsinogen (IRT) with the analysis of the most common mutations of the CFTR gene. The efficiency of this strategy is now well established, but the identification of heterozygotes among neonates with increased IRT is perceived as a drawback. We proposed to assess the heterozygosity frequency among the children with hypertrypsinaemia detected through the CF screening program implemented in Brittany (France) 10 years ago, to describe the CFTR mutations detected in them and to determine the frequency of the IVS8-5T variant. The molecular analysis relies, in our protocol, on the systematic analysis of three exons of the gene (7-10-11). A total of 160,019 babies were screened for CF in western Brittany between 1992 and 1998. Of the 1964 newborns with increased IRT (1.2%), 60 were CF and 213 were carriers. Heterozygosity frequency was 12.8%), i.e. 3 times greater than in the general population (3.9%; p < 10(-6)), Variability of mutations detected in carriers was greater than in CF children (21 mutations versus 10) and a high proportion of mild mutations or variants (A349V, R297Q, R347H, V317A, G544S, R553G, etc) was observed in carriers. The allelic frequency of the 5T (5.6%) was not significantly increased in this cohort. This study is consistent with previous ones in finding a significantly higher rate of heterozygotes than expected among neonates with hypertrypsinaemia. The strategy of screening used here allows to highlight the variability of mutations detected in heterozygotes and to show that severe mutations, as well as mild mutations, have been observed in neonates with hypertrypsinaemia. If there is no doubt that neonatal hypertrypsinaemia is associated with an elevated frequency of carriers, the underlying mechanisms remain obscure.

Neonatal screening for cystic fibrosis in Brittany, France: assessment of 10 years' experience and impact on prenatal diagnosis.

BACKGROUND: Neonatal screening for cystic fibrosis has been a subject of debate over the past few years. This study assesses 10 years of neonatal screening in Brittany, France, and examines its impact on prenatal screening of subsequent pregnancies in couples with an affected child. METHODS: The study included all the neonates screened for cystic fibrosis in Brittany from Jan 1, 1989, to Dec 31, 1998. The screening consisted of an immunoreactive trypsinogen assay from dried blood spots, plus, from 1993, mutation analysis. Data were collected on incidence of cystic fibrosis, and genotypic and biochemical characteristics. The use of prenatal screening of subsequent pregnancies in affected families was also investigated. FINDINGS: Of the 343,756 neonates screened, 118 children with cystic fibrosis were identified, giving an incidence of one in 2913. All mutated alleles were characterised: 34 different mutations resulting in 36 genotypes were detected. The introduction of DNA analysis into the protocol greatly reduced the recall rate and increased the sensitivity of the test. The mean cost of the screening programme was US$2.32 per screened child. 39 (34%) of the families identified by neonatal screening opted for subsequent prenatal diagnosis at least once. 12 couples would have benefited from this procedure while their first child was still symptom-free. 42 healthy children were born, and 18 pregnancies were terminated (therapeutic abortion rate of 100%). INTERPRETATION: We have shown the feasibility of neonatal screening for cystic fibrosis in Brittany. Through the detection of a large range of mutations, neonatal screening provides the opportunity for more reliable prenatal diagnosis and cascade screening. The neonatal screening programme described here could provide a good model for other countries intending to initiate such a scheme.