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EagI and NotI linking libraries were prepared in the lambda vector, EMBL5, from the mouse-human somatic cell hybrid 1W1LA4.9, which contains human chromosomes 11 and Xp as the only human component. Individual clones containing human DNA were isolated by their ability to hybridise with total human DNA and digested with SalI and EcoRI to identify the human insert size and single-copy fragments. The mean (+/- SD) insert sizes of the EagI and NotI clones were 18.3 +/- 3.2 kb and 16.6 +/- 3.6 kb, respectively. Regional localisation of 66 clones (52 EagI, 14 NotI) was achieved using a panel of 20 somatic cell hybrids that contained different overlapping deletions of chromosomes 11 or Xp. Thirty-nine clones (36 EagI, 3 NotI) were localised to chromosome 11; 17 of these were clustered in 11q13 and another nine were clustered in 11q14-q23.1. Twenty-seven clones (16 EagI, 11 NotI) were localised to Xp and 10 of these were clustered in Xp11. The 66 clones were assessed for seven different microsatellite repetitive sequences; restriction fragment length polymorphisms for five clones from 11q13 were also identified. These EagI and NotI clones, which supplement those previously mapped to chromosome 11 and Xp, should facilitate the generation of more detailed maps and the identification of genes that are associated with CpG-rich islands.

The WT1 gene was analysed using DNA from a Wilms' tumour derived from a patient with the WAGR syndrome using single strand conformation polymorphism analysis and polymerase chain reaction sequencing. A 14-bp insertion was found in the intron part of the splice donor site of exon 7 and was a tandem duplication of an upstream exon sequence. This mutation would be expected to disrupt the correct processing of the WT1 mRNA and is predicted to result in a non-functional protein. This observation further supports the role of WT1 in Wilms' tumorigenesis in patients with constitutional 11p13 deletions.

The Wilms' tumor predisposition gene, WT1, was analysed exon-by-exon in a variety of tumours using the single-strand conformation polymorphism (SSCP) technique. A consistent variation in the usual band pattern for exon 7 was detected in this survey. On sequencing, a silent mutation was noted in codon 313 resulting in an A-->G transition in an arginine codon. The A-->G transition destroys an AflIII restriction enzyme recognition site, which provides a rapid means of identifying heterozygotes at this locus. Analysis of the segregation of this polymorphism in families demonstrated a co-dominant inheritance pattern. In an analysis of 21 randomly selected individuals 25% were heterozygous at this locus, which makes this polymorphism useful in a variety of genetic analyses.

A cosmid library has been prepared in the lorist-B vector from a mouse/human somatic cell hybrid containing region 11q23-11pter as the only human component. This chromosome region is stably maintained in the hybrid as a result of translocation onto one copy of mouse chromosome 13. Individual cosmids containing human DNA were isolated by their ability to hybridise with total human DNA, digested with either HindIII or EcoRI, and 33 individual unique sequences were identified. These fragments were then isolated and subcloned into the bluescribe plasmid vector. Regional localisation of these unique sequences was achieved using a panel of somatic cell hybrids containing different overlapping deletions of chromosome 11. The majority of the 33 mapped sequences derived from the long arm of chromosome 11. Two clones were located within the 11p13-p14 region, which is associated with a predisposition to Wilms' tumour. These probes supplement those already mapped to this chromosome and will assist in the generation of a detailed chromosome 11 linkage map.

During routine screening of retinoblastoma patients for esterase D activity in red blood cell lysates a patient was identified with only 50% of normal enzyme activity. Chromosome analysis showed that this patient had a small deletion within chromosome region 13q14. Parental studies showed that, whereas the father had normal enzyme levels, the mother had esterase D levels which were also 50% of normal and a similar small 13q14 deletion. Ophthalmological examination failed to demonstrate any retinal abnormality in either parent. Thus we present the first case not only of the direct transmission of a 13q14 deletion within a family but also of an individual in whom the deletion has not predisposed to tumour formation.

We have analysed karyotypes and DNA from three patients with aniridia (congenital absence of irises) and Wilms' tumour. All three had constitutional deletions from the short arm of chromosome 11. The minimum region of overlap of the deletion involves a small region of band 11p13 presumed to contain the genetic loci responsible for both phenotypic abnormalities. Using cells from these patients, somatic cell hybrids with transformed mouse cells have been prepared. Individual subclones retaining either the deletion-11 chromosome or the normal chromosome 11, in addition to a variety of other human chromosomes, have been identified. The relative position of these breakpoints have been determined and the panel of hybrids has been used to map randomly-isolated 11p13 DNA sequences. The characterisation of these deletions has provided a useful panel of hybrids for random mapping strategies designed to identify the Wilms' and aniridia genes.

Somatic cell hybrids have been created between transformed mouse 3T3 cells and fibroblasts from a retinoblastoma patient with normal red-cell esterase-D (ESD) levels and a constitutional deletion of chromosome region 13q14-q31. In one subclone, which has retained the deletion chromosome but not the homologous normal copy, we have demonstrated the presence of the human ESD gene sequence. The breakpoint in this patient therefore must have occurred between the ESD gene and the retinoblastoma (Rb) predisposition locus. We have also been able to demonstrate that the ESD gene lies proximally to be the Rb gene in region 13q14. The recently isolated 4.7R cDNA gene sequence was absent from the deletion-containing hybrid, a finding consistent with the hypothesis that this sequence represents the Rb gene itself.