Eight common DNA polymorphisms have been described for the linked C6 and C7 genes. We now describe a ninth polymorphism in C7 exon 13 which is located in a tight cluster with two previously reported markers. We have used all these markers to investigate the heterogeneity of C7 deficiency. Five of the nine C7 deficient probands (resident in Ireland, South Africa, Russia and Israel) are heterozygous for C6/C7 haplotypes. Seven different C7 deficient haplotypes were found for C7 markers alone, but all the four Israelis share one and three out of four Irish haplotypes share another. The markers appear to be a good guide to the heterogeneity of C7 deficiency and have been useful in choosing homozygous subjects for the investigation of molecular defects.

We identified pepsinogen C (PGC) gene polymorphisms by means of PCR, which amplified DNA in the region within the intron between exons 7 and 8, and by 6% polyacrylamide gel electrophoresis. Six alleles were found in a Japanese population. The frequencies of these alleles in 408 unrelated Japanese individuals were 0·074, 0·026, 0·335, 0·237, 0·016 and 0·314, respectively. The serum pepsinogen II level significantly decreased in the order of the allele 6 homozygote, the allele 6 heterozygote and the other genotypes (χ2=7·850, D.F.=2, p=0·020). These findings indicated that the genetic background of serum pepsinogen should be considered when screening for stomach cancer by this procedure.

A new AAT allele (PI Zbristol) has been discovered in a woman with an obstetric history of three perinatal deaths from fulminant liver disease and no living offspring. She and her father were both PI M1Zbristol heterozygotes. The Zbristol protein is active as a proteinase inhibitor but appeared to be deficient in the plasma to about the same degree as the S protein in MS heterozygotes. It focuses on the basic side of Z and lacks the normal pattern of secondary isoforms associated with the commonly occurring AAT variants and migrates faster than normal on an SDS electrophoresis gel. The Zbristol mutation was found to be a C to T transition at codon 85 changing ACG (Thr) to ATG (Met). This disrupts the N-glycosylation site starting at Asn 83 preventing glycosylation at residue 83 in the PI Zbristol protein and explains the protein isoelectric focusing and SDS gel electrophoresis results. An analysis of haplotypes in the propositus and her father indicated that the Zbristol mutation occurred on the common M1(Val 213) genetic background. The new mutation also led to the generation of an NlaIII restriction endonuclease recognition site. Cell lines from two offspring tested for the presence of this NlaIII site revealed that one had the variant and the other did not. Thus, the relationship between Zbristol and fulminant liver disease in the offspring is unclear.

Every science has roots that antedate acceptance as a discipline. Neglecting these intimations, there is a consensus that population genetics became a recognised science about 1920, and that it split into two branches about 1960. One branch is concerned with historical processes, uniting genetics with anthropology and (in other species) with paleontology and taxonomy. The other branch is concerned with inheritance in contemporary populations, uniting genetics with epidemiology, medicine, psychology, and (in other species) with agriculture. Anthony Edwards (1995) identified this dichotomy as ‘differential-equation biology’ vs ‘statistical biology’. The distinction becomes fastidious when current gene frequencies are taken as indirect evidence for selection by disease in the remote past: such inference from a unique event is more characteristic of evolutionary genetics but concerns all population geneticists. From time to time interest groups are formed around twins, behaviour, demography, or quantitative traits, but they are generally recognised as aspects of genetic epidemiology. If the young science is in jeopardy, it is not by fission but by exclusion of studies that are only indirectly related to disease, which provides a focus but does not specify the contents. I will argue that every aspect of population genetics that is not primarily concerned with evolution is part of genetic epidemiology, and that the field must suffer if it is not inclusive. As with all human activity progress is punctuated, often cyclical, and therefore suggests the real and apparent movement of celestial bodies for which the language of astronomy is appropriate.

The Fifth International workshop on chromosome 9 comprised a gathering of 36 scientists from seven countries and included a fairly even distribution of interests along chromosome 9 as well as a strong input from more global activities and from comparative mapping. At least eight groups had participated in the goal set at the previous workshop which was to improve the fine genetic mapping in different regions of chromosome 9 by meiotic breakpoint mapping in allocated regions and this has resulted in some greatly improved order information. Excellent computing facilities were available and all contributed maps were entered not only into SIGMA (and thence submitted to GDB) but also into a dedicated version of ACEDB which can be accessed on the Web in the form of one of 28 slices into which the chromosome has been arbitrarily divided. It was generally agreed that the amount of data is now overwhelming and that the integration and validation of all data is not only unrealistic in a short meeting but probably impossible until the whole chromosome has been sequenced and fully annotated. Sequence-ready contigs presented at the meeting totalled about 3 MB which is about one fiftieth of the estimated length. The single biggest barrier to integration of maps is the problem of non-standard nomenclature of loci. In the past 2 workshops efforts have been made to compare traditional ‘consensus’ maps made by human insight (still probably best for small specific regions) with those generated with some computer assistance (such as SIGMA) and those generated objectively by defined computer algorithms such as ldb. Since no single form of map or representation is entirely satisfactory for all purposes the maps reproduced in the published version of the report are confined to one of the genetic maps, in which Genethon and older markers have been incorporated, a Sigma map of the genes as symbols together with a listing of known ‘disease’ genes on chromosome 9, and a revised assessment of the mouse map together with a list of mouse loci predicted to be on human chromosome 9. One of the 28 ACEDB slices is also shown to illustrate strengths and weaknesses of this approach. Workshop files include not only all maps available at the time but also details of loci and details of the meiotic breakpoints in the CEPH families (http://www.gene.ucl.ac.uk/scw9db.shtml).

This report and other information on chromosome 9 can be found on the chromosome 9 homepage at the URL: http://www.gene.ucl.ac.uk/chr9/

Two hundred and eleven patients with a clinical diagnosis of Turner syndrome were studied. We report (i) the cytogenetic results, (ii) the frequency of cryptic mosaicism and (iii) the parental age and the parental origin of the abnormality. We scored 100 cells from blood cultures and found 97 patients to have a 45,X constitution, 15 to be 45,X/46,XX or 45,X/47,XXX mosaics, 86 to have a structurally abnormal X and 13 to have a structurally abnormal Y chromosome. Molecular methods were used to look for cryptic X and Y chromosome mosaicism in patients with a 45,X constitution. Two cryptic X but no cryptic Y mosaics were detected. In 74% of the 45,X patients the X was maternal in origin. The i(Xq)s were approximately equally likely to involve the paternal or maternal chromosome, while the majority of deletions and rings and virtually all the abnormal Y chromosomes were paternal in origin. We suggest that the preponderance of paternal errors in Turner syndrome may result from the absence of pairing along the greater part of the XY bivalent during paternal mei I, which may make the sex chromosomes particularly susceptible to both structural and non-disjunctional errors during male gametogenesis.

Phosphoglucomutase 1 (PGM1) deficiency is a stable characteristic of the erythroleukaemic cell line, K562, whereas the activity of the isozymes of the other two PGM loci (PGM2 and PGM3) is slightly elevated. In this study the molecular basis of PGM1 deficiency was investigated by a combined approach utilising protein electrophoresis, immunodetection, cytogenetic techniques, and DNA and RNA analysis. Isoelectric focusing and activity staining confirmed that K562 has no detectable PGM1 activity. Immunoblot analysis of extracts, separated by isoelectric focusing, starch gel and SDS gel electrophoresis, using monospecific anti-PGM1 antibodies showed that K562 contained no detectable immunoreactive material. Karyotype analysis revealed the presence of two intact chromosomes 1 and a derivative chromosome 1, der(1)t(1; 11), each of which carried a copy of the PGM1 gene as demonstrated by fluorescence in situ hybridization using a PGM1 cosmid as probe. Southern blot analysis using a PGM1 cDNA clone as probe suggested that the PGM1 genes had not been subject to any gross structural rearrangements. We were also able to determine that K562 is type PGM1 2+1+ by restriction endonuclease analysis of genomic DNA. Very low levels of PGM1 mRNA which appeared to be full length transcripts were detected in K562 using a reverse transcriptase PCR technique. We conclude that the most likely cause of PGM1 enzyme deficiency in K562 is abnormal regulation of transcription.

Through linkage analysis and the identification of structural chromosome rearrangements, a number of disease genes have been mapped to the pericentromeric region of the long arm of chromosome 13. Structural rearrangements, or deletions, of the 13q12 region have been implicated in a range of myeloproliferative neoplasms, and other haematopoietic malignancies. In particular, seven cases of a t(8;13) (p11; q12·1) rearrangement have been noted in patients with an atypical myeloproliferative disorder associated with T-cell leukemia and eosinophilia. We have previously identified a CEPH megaYAC, 943E4, which crosses the translocation breakpoint in archival tumour samples from two patients with this t(8;13) translocation. As an initial step in the characterisation of this translocation breakpoint, we have generated a fine structure physical map of this 1·9 Mb YAC. We have used the method of YAC fragmentation to generate a series of deletion constructs of known size, which provide discreet physical landmarks convenient for mapping genetic markers along the 943E4 YAC. Analysis of these deletion constructs defined the order of ESTs and microsatellite markers in 943E4 as: cen-NIB1257-(ATP1AL1/D13S283)- D13S179E-(D13S504E/D13S505E)-D13S824E-D13S182E-D13S221-tel. These markers have also been assigned to physically defined regions relative to the fragmented YAC endpoints and a derived NotI restriction map.

The caudal-type homeobox gene Cdx2 encodes a transcription factor which is expressed in the intestine and is thought to play an important role in the proliferation and differentiation of intestinal epithelial cells. Mice heterozygous for null mutations in the caudal-type homeobox gene Cdx2 show multiple adenomatous polyps in the proximal colon in addition to skeletal problems associated with abnormal segmentation. In human colorectal cancer the expression of both CDX2 and carbonic anhydrase 1, a gene regulated by CDX2, is reduced or absent. It is possible that mutation of CDX2 is a primary event in the origin of some colorectal cancers. We have cloned human CDX2 cDNA and report here the nucleotide and protein sequences and assignment of the human gene to chromosome 13q12–13.

We have undertaken a study of 35 patients with i(Xq) to determine whether those that are maternally derived originate by similar mechanisms to those that are paternally derived. Isochromosome formation is not associated with increased parental age and >90% of i(Xq) contain proximal Xp sequences suggesting that centromere misdivision is not a common mechanism of formation. Our results indicate that the majority of i(Xq) originate from a single X chromosome and the usual mechanisms of formation do not appear to differ according to the parent of origin.

RALGDS is a 115 kDa protein which was identified by its ability to enhance guanine nucleotide exchange for the ras family member ral. It also binds to activated ras and rap1, and appears to function as part of a signalling complex in downstream events following rap1 activation. Here we report the identification of full-length cDNA clones for human RALGDS, isolated from a brain cDNA library. The predicted protein has strong sequence homology to rat and murine isoforms of RALGDS in the N- and C-terminal regions, but an internal region (aa 250–380) shows relatively high divergence with only 42% identical amino acid residues. The human RALGDS gene is contained within a 30 kb region of 9q34, approximately 200 kb proximal to the ABO gene, within the current critical region for the tuberous sclerosis gene TSC1. Partial genomic structure was determined; it consists of at least 11 exons. Based upon analysis of Southern blots from 110 TSC patients, genomic DNA SSCP analysis, and RT-PCR analysis which demonstrated RNA expression of both alleles in patients from 9q34-linked TSC families using intragenic polymorphisms, we conclude that RALGDS is not likely to be TSC1.

The transcription map of the human genome published by Schuler et al. (1996) is a valuable resource in which approximately one quarter of all human genes have been mapped with respect to genetic framework markers using radiation hybrids. We have taken information from this map to provide potential genes within the TSC1 candidate region on chromosome 9q34. In so doing we have been able to provide an independent assay of the quality of the radiation hybrid mapping by using somatic cell hybrids and a 2 Mb cosmid contig covering the TSC1 region as mapping tools. In addition, we have built sequence contigs of ESTs for 25 clusters. This has shown that about 20% of the relevant EST clusters in the Unigene resource (Boguski & Schuler 1995) contain chimaeric clones.

When dominant mutations of different genes may lead to the same disease, it is often difficult to detect in a particular patient which gene is involved. A strategy is to make genealogical extensions to find affected relatives that should have inherited the same mutation. In particular, for diseases with late age of onset or short survival time, only poor information may be obtained from close relatives of probands and it can be particularly efficient to make genealogical extensions to detect pairs of distantly related affected individuals. Such a pair of affecteds may provide information concerning the region of the genome where the mutated gene should map. Two situations may be encountered depending on whether or not prior information on the location of mutated genes involved in the disease are available. If we already know, from previous linkage studies, that a gene located in a given region R of the genome may be involved in the disease, the problem is then to confirm that it is indeed a mutation of this gene that is involved in the affected pair. Once the implication of a gene in region R has been confirmed the affected pair of relatives may give information to restrict the length of this region R. In this paper we discuss these two points by deriving analytically first the lod score expected and second the expected reduction of the length of the region where the mutation is suspected to map as a function of the number of meioses between the two affected individuals and of the polymorphism of the markers available in the region.

Complex segregation analysis was conducted in a series of patients with hereditary non-polyposis colorectal cancer (HNPCC) ascertained through probands registered in the Cancer Registry of the Health Care District of Modena, Northern Italy. Altogether there were 125 nuclear families segregating for HNPCC, for a total of 672 individuals. The analysis favoured a two-locus model, with both susceptibility genes rare and dominant. The gene frequency of the deleterious allele at the major locus is estimated to be low qm=0·004 and for the second locus the estimate is even lower q=0·00003. Both genes defining the two-locus model seem to be highly penetrant. The lifetime penetrance of the abnormal gene at the major locus is estimated to be 0·73 for female, while the estimation for male is higher, 0·85.

A patient (64-year-old, male) with familial cholinesterasemia caused by BChE deficiency was studied. DNA sequence analysis of all exons identified a point mutation, an A→G transition at codon 128, resulting in a Tyr→Cys substitution. The propositus showed extremely low BChE activity, but his other family members (three individuals) showed from intermediate to normal BChE activity. An immunological method revealed the absence of BChE protein in serum of the propositus. Both PCR primer introduced restriction analysis (PCR-PIRA) and sequence analysis revealed all three family members to be heterozygotes for this mutation.

In order to assess the effect of the HLA region on familiality of coeliac disease (CD), we carried out a study on 121 CD index cases and 325 first degree relatives. The transmission disequilibrium test confirmed the importance of the HLA-DR3 haplotype in CD susceptibility. However, the different distortion found in affected children inheriting maternal or paternal DR3 alleles suggested that the sex of the parent might influence the risk conferred by this haplotype. The increase in risk to siblings of affected individuals relative to the risk in the general population (λs) and the contribution of the HLA genes to this clustering (λsHLA) have also been estimated. Non-overlapping data from the literature have been collected and combined with our sample to extend such analysis. Then, the percentage contribution of the HLA region to the development of CD among siblings was 36·2%. This result confirms that the HLA genotypes are an important genetic background to CD development but shows that additional susceptibility factors remain to be identified.

The transmission disequilibrium test (TDT) is a simple means to detect association which should only be positive if the marker allele is linked to the disease locus, but it cannot be used if parents of affected subjects are unavailable, as can occur when the disease has a late age of onset. Although one can sometimes deduce parental genotypes using the siblings of affected cases, reliance on this procedure can introduce bias and may also result in discarding many families which could provide useful information. Instead, it is shown that the use of unaffected siblings as controls is, like the TDT, robust against bias due to population stratification and other sources, and is expected only to produce positive results when a marker is both associated and linked with the disease locus. The method can have much less power than a case-control study using unrelated controls, but this can be guarded against by seeking unaffected siblings which are genotypically distinct from cases and by focusing only on alleles which are different within pairs of cases and controls. This yields a pair-wise test for association which can be used for multiallelic markers in a manner exactly analogous to the extended TDT (ETDT). The use of siblings as controls is simple, robust, practical and worthy of further consideration.

Co-segregation studies based on a selection of intragenic restriction fragment length polymorphisms of the low density lipoprotein receptor (LDLR) gene have been used extensively both for research and diagnostic studies of familial hypercholesterolaemia (FH) families, because direct mutation screening remains complex. Here we describe the development and application of a more efficient approach to co-segregation studies based on highly informative dinucleotide and tetranucleotide repeats flanking the LDLR gene. A series of microsatellites (D19S391, D19S394, D19S221 and D19S179) were selected for study on the basis of linkage analysis in the CEPH families using intragenic polymorphisms for a TA repeat (exon 18) in the LDLR gene, and earlier data for a Pvu II polymorphism (intron 15). A physical map of the region of chromosome 19 also contributed to this selection. One marker in particular, D19S394, sited 150 kilobases telomeric to the gene, was extremely useful, displaying 90% heterozygosity, robust PCR of tetranucleotide repeats without stutter bands, and no recombination with the LDLR gene (θ=0, LOD 68). Use of this marker in the families of twenty-three FH probands from Hampshire demonstrated co-segregation of the hyperlipidaemia phenotype with the LDLR gene region, except in one family with defective apolipoprotein B-100, and a family turning out to display familial combined hyperlipidaemia. This approach should facilitate the search for any families where FH does not co-segregate with the LDLR gene, and will enhance the repertoire of molecular diagnostic tools available for FH.