Background: The demand for prenatal diagnosis (PD) of cystic fibrosis (CF) is increasing.
Methods: We performed pre-test multidisciplinary counselling for 192 couples at CF reproductive risk. In 11/192 (5.7%) cases PD was not performed mainly because counselling revealed a reproductive risk for atypical (mild) CF, while 181 PDs were performed in couples revealed at high risk for CF mainly because they already had a CF child (148/181, 81.8%) or had been identified through cascade screening (28/181, 15.5%).
Results: In 167/181 (92.3%) cases (including two dichorionic twin pregnancies), PD was performed on chorionic villi, and in 14 on amniocyte DNA. Only 1/181 PD was unsuccessful. In all other cases, single tandem repeat analysis excluded maternal contamination, and PD was made within 7 days of sampling. In total 116/180 (64.4%) PDs were made with dot-blot analysis; 40 (22.2%) required gene sequencing; in 4/180 cases we tested the gene for large rearrangements; in 23/180 (12.8%) cases linkage analysis was necessary because parental mutation(s) were unknown. Forty-two out of 180 (23.3%) PDs revealed an affected foetus. All couples but one interrupted pregnancy. The first twin PD revealed the absence (1 foetus) and the presence of one mutation (the other foetus); the second twin PD revealed one parental mutation (1 foetus) and both parental mutations (the other foetus); the couple planned selective interruption.
Conclusions: PD for CF should be performed in reference laboratories equipped for gene scanning and linkage analysis, with a multidisciplinary staff able to offer counselling to couples during all phases of PD.
Haemophilia A is the most common inherited bleeding disorder caused by defects in the F8C gene that encodes coagulation factor VIII. This X-linked recessive disorder occurs in approximately 1:5000 males. Haemophilia A is diagnosed based on normal prothrombin time, altered activated partial thromboplastin time and reduced factor VIII activity in plasma. Carrier females are usually asymptomatic and can be identified only by molecular analysis. The most frequent mutations in F8C are intron 22 and 1 inversions, which occur in approximately 50% and 5% of patients, respectively, with a severe phenotype. Large gene deletions are observed in approximately 5% of alleles from patients with severe haemophilia A. The remaining severe cases and all moderate and mild cases result from numerous point mutations and small insertions/deletions, which are de novo mutations in one-third of cases. Thus, molecular diagnosis of carrier status and prenatal diagnosis in families without intron 22 or 1 inversions is based on scanning techniques or gene sequencing. When the disease-causing mutation cannot be identified, molecular diagnosis is performed by linkage analysis of several DNA polymorphic markers linked to F8C. Given the clinical heterogeneity among haemophilic patients, many groups, including our own, have examined the relationships between prothrombotic gene variants and haemophilic phenotype to investigate whether prothrombotic gene variants modify clinical expression of the disease.
Thanks to its typical expression, haemophilia can be identified in writings from the second century AD. Haemophilia B, an X-linked recessive bleeding disorder due to factor IX (FIX) deficiency, has an incidence of about 1:30000 live male births. The factor 9 (F9) gene was mapped in 1984 on Xq27.1. Haemophilia is diagnosed from prothrombin time, activated partial thromboplastin time, and FIX levels. Carrier females are usually asymptomatic and must be identified only with molecular analysis. Linkage analysis of F9 polymorphisms is rapid and inexpensive but limited by non-informative families, recombinant events, and the high incidence of germline mutations; thus, various procedures have been used for the direct scan of F9 mutations. We set up a novel denaturing high performance liquid chromatographic procedure to scan the F9 gene. This rapid, reproducible procedure detected F9 mutations in 100% of a preliminary cohort of 18 haemophilia B patients. Parallel to the development of more efficient diagnostic tools, the life expectancy and reproductive fitness of haemophilic patients have greatly improved and will continue to improve thanks to the use of less immunogenic recombinant FIX. Hopefully, new approaches based on gene therapy now being evaluated in clinical trials will revolutionise haemophilia B treatment.