Presymptomatic testing was done on four people from a large family in which an autosomal dominant form of spinocerebellar ataxia was segregating. Earlier genetic analysis had shown that in this family the disorder was tightly linked to an informative microsatellite polymorphism on chromosome 6p. Two subjects with prior risks of 50% of developing the disease had final risks after testing of 2%; the other two with prior risks of 25% had final risks of 1%. Chromosome 6p linked spinocerebellar ataxia may now be added to Huntington's disease as a late onset disorder in which genetic linkage may be used to carry out presymptomatic testing.

A family carrying two cystic fibrosis mutations, delta F508 and 1717-1, G --> A, requested prenatal diagnosis. In order to eliminate the need for labelling of allele-specific oligonucleotides and to simplify the analysis, 1717-1, G --> A was detected using an ARMS (amplification refractory mutation system) method (Newton et al., 1989). Fetal DNA was obtained by chorionic villus sampling (CVS) and the ARMS technique was used to exclude the 1717-1, G --> A mutation. The fetus was found to be heterozygous for the delta F508 mutation. ARMS is a simple, quick, non-radioactive method suitable for detecting DNA mutations in various clinical situations.

We have screened 100 partners of known or suspected CF heterozygotes for ten CF mutations which account for 88% of the CF mutations seen by us on CF chromosomes. We have identified six CF heterozygotes amongst the 100 low-risk people screened. As two of the six people at high-risk of being CF carriers were subsequently shown not to be CF carriers this gave rise to four couples with a one in four risk of CF in a pregnancy and so far to two PND's. The risk of CF in the remaining 94 couples was reduced to less than one in 800. We have concentrated on the screening of partners for the commoner CF mutations rather than haplotyping them for the CF linked markers XV-2c/TaqI and KM19/PstI which are in linkage disequilibrium with CF. For individuals shown not to carry these ten mutations, a five fold difference in risk of being a CF carrier remains between those who have the XV-2c/KM19 genotypes associated with the highest risk(BB), as compared to those with the lowest risk(CC). Nevertheless we feel that effort is better expended in mutation screening rather than haplotyping.

out in the more conducive environment of NHS facilities.We have serious doubts regarding the viability of the scrutiny team's proposals; in particular we believe that the purchasers (the prison service) will not be able to find adequate providers (NHS doctors).A corps of part time doctors devoted to the service already exists, but experience tells us that few others are likely to last the course.

In a Scottish family in which Huntington's disease (HD) was segregating, recombination was observed between the D4S115/S111 and D4S43/S95 loci, with the HD gene associated with the more proximal D4S43/S95 locus. Analysis of linkage disequilibrium in Scottish families showed significant non-random association between the HD gene and alleles at the D4S95 and D4S98 loci. This adds to previous evidence that the HD locus is not sited at the telomere of chromosome 4.

A hybrid cell line (R21/B1) containing a truncated human chromosome 6 (6pter-6q21) and a human Y chromosome on a hamster background was irradiated and fused to A23 (TK-) or W3GH (HPRT-) hamster cells. Clones containing expressed HLA class I genes (4/40) were selected using monoclonal antibodies. These clones were recloned and analyzed with a panel of probes from the HLA region. One hybrid (4G6) contained the entire HLA complex. Two other hybrids (4J4 and 4H2) contained only the HLA class I region, while the fourth hybrid (5P9) contained HLA class I and III genes in addition to other genes located in the 6p21 chromosomal region. In situ hybridization showed that the hybrid cells contained more than one fragment of human DNA. Alu and LINE PCR products were derived from these cells and compared to each other as well as to products from two somatic cell hybrids having the 6p21 region in common. The PCR fragments were then screened on conventional Southern blots of the somatic cell hybrids to select a panel of novel probes encompassing the 6p21 region. In addition, the origin of the human DNA fragments in hybrid 4J4 was determined by regional mapping of PCR products.

a gene is cloned and identified through knowledge of its expressed protein product, the new genetics works in reverse and uses information on gene structure to infer the amino acid sequence and function of the protein it controls. For this reason the phrases 'new genetics' and 'reverse genetics' have become largely synonymous. An outline of the major steps in reverse genetics is shown in Figure 1. Although it was apparent in 1979 that a technology existed which should in principal allow the identification of genes responsible for most Mendelian disorders, it was 10 years before a human gene was cloned by a pure reverse genetic approach without

We present an analysis of the frequency of 16 different cystic fibrosis (CF) mutant alleles in the Scottish population. Each allele was detected in DNA amplified by the polymerase chain reaction (PCR) either directly on polyacrylamide gels, on agarose gels after restriction enzyme digestion, or by using allele specific oligonucleotides. Among 506 CF chromosomes, of predominantly Scottish origin, the frequencies of the different mutations were delta F508 0.71, G551D 0.05, G542X 0.04, R117H 0.01, 1717-1G----A 0.01, A455E + delta I507 + R553X + R560T + W1282X + 621 + 1G----T combined 0.03, unpublished 0.01, and unknown 0.13. No examples of D110H, R347P, S549N, S549I, or 2566ins AT mutations were found. The relevance of this type of analysis for both prenatal diagnosis and heterozygote screening is discussed.