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/

In order to explore the nature of glucose-6-phosphate dehydrogenase (G6PD) deficiency in south-east Sicily, we have analysed the G6PD gene in 25 unrelated males with abnormal G6PD activity and/or electrophoretic mobility, by using the analysis of the appropriate PCR-amplified fragment of DNA and subsequent digestion by appropriate restriction-enzymes, looking for the presence of certain known G6PD mutations. We amplified the entire G6PD coding sequence into eight fragments, followed by single-strand conformation polymorphism (SSCP) analysis and sequencing of those individual fragments that were found to be abnormal by SSCP. Through these methods we found a total of twelve G6PD Mediterranean variants with the association of a silent mutation 1311 (also known as polymorphic site Bcl I), one G6PD Mediterranean without this association, four G6PD A− Val 68 and two G6PD Santamaria and five G6PD Chatham. In a subject with normal activity a mutation was found in exon 5, designated as G6PD Sao Borja. This is the first report on the molecular analysis of G6PD mutations in Sicily and we have obtained evidence for four distinct classes of variants.

Sjögren–Larsson syndrome (SLS), a rare autosomal disorder characterized by ichthyosis, spastic neurological disorders and oligophrenia, is associated with deficiency of fatty aldehyde dehydrogenase encoded by a gene on chromosome 17q11.2. Mutations of the gene (GDB symbol ALDH10) were recently identified in three SLS patients. Another aldehyde dehydrogenase isozyme, ALDH3, also has a high activity for fatty aldehyde oxidation, and is encoded by a gene in chromosome 17q11.2. Abnormality of the ALDH3 gene could also cause a similar syndrome.

The examination of the ALDH3 locus of three additional SLS patients showed that two are heterozygous with C→G at nt 985 (Pro→Ala at protein position 329). However, the mutation was found to be common (frequency of the atypical allele is about 0·25) in normal subjects, and not related to SLS.

Isoelectric focusing analysis indicated that ALDH3 is hardly expressed in normal as well as patients' fibroblast cells, while ALDH10 expressed in the normal cells is diminished in the three patients' cells. The level of ALDH10 mRNA is also low in the patients' cells.

The examination of the ALDH10 locus revealed the existence of a 3 base deletion coupled with a 21 base insertion at intron 6/exon 7 junction in one patient. This abnormality is the same as that found in the patient previously reported by other investigators. One patient is associated with a 2 base deletion at nt 1297 and consequent premature chain termination at protein position 434. Another patient is a compound heterozygote for the same 2 base deletion at nt 1297 and a 5 base insertion at nt 1311 and premature chain termination at protein position 457. Unique characteristics of the SLS mutations are pointed out.

Despite the recent cloning of BRCA1, BRCA2 and the mismatch repair genes, it will still be a long time before it is possible to specify any individual's risk for ovarian cancer based on her genotype. Most women concerned about their risk on the basis of one or two affected relatives do not belong to extensive ovarian cancer families. Risk calculations depend on a reliable genetic model for ovarian cancer derived, ideally, from the population from which an individual is drawn. We have carried out a segregation analysis using data collected from consecutive ovarian cancer patients in two different centres in the UK. Complex segregation analysis was carried out with the addition of diathesis as a separate parameter allowing other cancers, associated with ovarian cancer, to be taken into account. The use of diathesis in the derivation of this alternative model is described. Analysed under joint likelihood without diathesis, the gene frequency is 0·0028 and penetrance to age 70 years is 50%. This is in agreement with other published models. Incorporating diathesis into the model under joint likelihood gives similar parameters for a single locus model but gives the best fit with a two locus model where both genes are rare.

Haseman & Elston (1972) introduced a sib pair method using classical regression analysis to detect linkage between a polymorphic marker locus and any quantitative trait locus. Most of the diseases mapped to date follow simple Mendelian, single locus transmission. But there are many familial diseases that do not follow simple Mendelian segregation, for example diabetes, several forms of cancer, etc. In this paper, we extend Haseman and Elston's sib pair method to two unlinked quantitative trait loci each linked to one of two unlinked polymorphic marker loci. For the two-locus epistatic model, we give a general formulation of the complete regression model and details of the regression coefficients in terms of variance components.

The Haseman & Elston (1972) sibling-pair regression method has been used to detect and estimate the variance contribution to observed values of a quantitative trait by allelic variation in specific candidate genes. The procedure was developed under a model with a single biallelic trait locus. This assumption does not hold for several known systems. In this paper we prove that for candidate gene analysis the Haseman–Elston procedure extends to the case of multiple trait loci, each possibly having more than two alleles. Simulation experiments comparing single-locus to two-locus models show that fitting the extended regression equations maintains nominal significance levels, but the power to detect linkage to trait variation is not improved by including additional loci. These results indicate that the original proposal is statistically robust to violations of the underlying genetic model. Practical issues associated with quantifying the relative variance contribution by individual loci are also discussed. Applications of the extended regression equations to lipoprotein(a) and high density lipoprotein cholesterol are given for illustration.

A new CYP17 gene abnormality was found in three Japanese patients with 17α-hydroxylase deficiency (17OHD). These patients were children from consanguineous marriages, but from two apparently unrelated families: one patient with 46, XY karyotype, and two siblings with 46, XX and 46, XY karyotypes. They were all raised as girls and presented with amenorrhea, eunuchoid appearance and hypertension. Gene analysis revealed two base-pair (TG) deletion in exon 5 (codons 300, 301) of the CYP17 gene. This deletion could be expected to alter the reading frame resulting in the lack of a haem-binding region (Cys 442) due to a premature stop codon at position 333. This small mutation may account for the patients' clinical manifestations of 17OHD.