A pilot project offering voluntary heterozygote screening for the delta F508 mutation causing cystic fibrosis (CF) to 638 pregnant women attending two antenatal clinics in the eastern part of Berlin was carried out from 1990-1993. Participation was invited using an information leaflet and inclusion in the study was conditional on written informed consent. Of those invited to participate, only one refused to be tested, on the grounds of non-acceptance of prenatal diagnosis. Eighteen pregnant women were identified as carriers of the delta F508 mutation. All of them and their male partners accepted counselling in which the genetics of CF, its prognosis and treatment were explained, with emphasis on the meaning of heterozygosity, the fact that carriers are healthy, and the risk of an affected fetus when only one parent is identified as a heterozygote. All partners agreed to be tested for the delta F508 R553X and G551D mutations and a second counselling session was carried out after this test result was available. No problems were observed during initial testing but, as in other studies, we found considerable anxiety on being given the result in all couples where the woman tested positive; this was reduced substantially by counselling and when the partner tested negative. All probands found to be carriers stated that they found screening acceptable. In contrast to the cautious statement by the German Berufsverband Medizinische Genetik and the hostile reaction from a representative of the CF self-support organisation towards community-based heterozygote screening for CF, this study shows that CF screening is generally acceptable in this German population and that it is actively taken up by most pregnant women when offered.

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We analyzed germline mutations of the BRCA1 gene in 20 German breast/ovarian-cancer families. BRCA1 mutations co-segregating with breast-cancer susceptibility were identified in 3 of these families. All mutations were found to generate a premature stop codon leading to the synthesis of truncated BRCA1 proteins of different length. Nine polymorphisms were detected in BRCA1, 4 of which have not been described previously. Analysis of familial tumors for LOH revealed that only the disease-related allele of BRCA1 was present.

Optimal temperature conditions for the detection of 28 known mutations on 15 exons of the human cystic fibrosis transmembrane conductance regulator gene by single strand conformation polymorphism analysis using the Diagen TGGE Apparatus were established. This procedure was applied to the detection of unknown mutations in 58 non-deltaF508 chromosomes. Three novel mutations, -471del3 (5' flanking region), 3171insC (exon 17a) and 4700(T)8/9 (3' non-translated region) of the CFTR gene were found. Mutation 3171insC occurred in conjunction with the delta F508 mutation on the other allele of a child presenting with severe pathology. Mutation -471del3 has so far only been found in one healthy individual and her father, and 4700(T)8/9 is a DNA sequence polymorphism.

SUMMARY Two cDNA probes, cf23a and cf56a, identify deletions of selected exons in about 50% of our DMD/BMD patients. We have estimated the most likely order of the 11 exons detectable with both probes with respect to the different extensions of the deletions. In one of our BMD pedigrees, the observed deletion could be traced in the affected males through three generations. This result shows that with the use of cDNA probes detecting deletions, the only risk of error in genomic prenatal diagnosis is the general high frequency of new mutations for DMD/BMD. This is important progress in diagnosis compared to the 2 to 5% risk of misdiagnosis 'because of crossing over events using conventional linkage analysis with bridging or intragenic probes. The first prenatal diagnosis of an unaffected fetus of a woman who is a DMD carrier according to ultrasound examination is described. In one of our DMD males, the cDNA probe cf56a detects a deletion breakpoint. His sister also shows the altered band and is therefore a DMD carrier, while his mother has a totally normal band pattern. The interpretation of this observation could be either germline mosaicism or two identical new mutations. The identification of deletion breakpoints is a new diagnostic strategy, especially for carrier determination, which excludes misdiagnosis owing to crossing over events and the problems of dosage estimation. It is, however, limited by the low frequency of breakpoints detectable with cDNA probes. Therefore, the generation of new intron probes in this region is an important goal.Duchenne muscular dystrophy (DMD) and its clinically milder allelic form, Becker muscular dystrophy (BMD), are the most common X linked recessive genetic disorders affecting about one in 3000 males. DNA diagnosis has resulted in dramatic progress in carrier detection and prenatal analysis for affected families.1-3 However, since up to now it has been predominantly based on linkage analyses, its reliability was limited by the possibility of crossing over events. This has caused difficulties in decision making for pregnant women, particularly in prenatal diagnosis.

Sixty-eight DMD patients without detectable deletions or duplications were analysed, resulting in the identification of a point mutation in the coding sequence and two polymorphisms in the 5' flanking intron. The C to T change of the first nucleotide in the third triplet leads to a stop codon and seems to be the cause of the functional deficiency of the gene product in this patient.

A theoretical and practical approach to economize the analysis of large DNA sample numbers for identifying heterozygosity of the delta F508 mutation causing cystic fibrosis is presented. Sample pooling can reduce the number of polymerase chain reaction (PCR) tests for this mutation by up to 77%. Based on a mathematical model, the optimal number (n) of samples to be united in one pool is 24 for a German population with a delta F508 heterozygosity incidence of about 1/35. We show that the PCR method is sufficient to detect one heterozygote for the delta F508 mutation in a pool of up to 49 non-delated DNA samples.

More than 100 mutations have been described for the breast-cancer-susceptibility gene BRCA1. The paper describes phenotypical aspects of three selected mutations located at the beginning, in the middle, and at the end of the gene. A remarkable decrease of the age of diagnosis of the mammary carcinoma is observed with increasing length of the putative gene product, combined with greater severity of the disease.