In an ancient fishing village in the neighbourhood of Leiden a cluster of melanoma-prone families was detected. In these families atypical precursor naevi were recognizable in many melanoma patients and in their relatives. This combination of symptoms is called the Dysplastic Naevus Syndrome (DNS). The spectrum of clinical signs characterizing the phenotype of the DNS ranged from apparent lack of gene-expression through minimal to obvious manifestations. Genetic analysis of six pedigrees revealed an autosomal dominant mode of inheritance, with a very variable expressivity of the gene, which is also rather frequently non-penetrant. The total number of family members (affected or at risk) was 314, 243 of which were alive and were personally examined by us. In the six pedigrees a total of 33 patients with melanoma occurred. In thirty patients with multiple atypical naevi, the clinical diagnosis of DNS was histologically verified. A further thirty-six patients with several atypical naevi were also regarded as gene carriers. Fifteen 'normal' individuals had to be gene-carriers on the basis of their position in the pedigree.

We describe a family with an increased frequency of cells with premature centromere division (PCD) of all chromosomes in four phenotypically normal individuals. This familial PCD phenomenon is apparently different from the well-described PCD of the X chromosome and from the centromere splitting in cells of patients with Roberts syndrome. Implications for genetic counseling are discussed.

We have examined the procollagens and collagens produced by skin fibroblasts from a patient with Ehlers-Danlos syndrome type VII. The patient was heterozygous for an abnormal alpha 2(I) chain migrating with the approximate size of pN alpha 2(I) chains after pepsin digestion. Peptide mapping suggested that the abnormality was located at the amino-terminus of the alpha 2(I) chain. Quantitative analysis of the alpha 2(I) mRNA indicated loss of the exon 6 sequences, and subsequent polymerase chain reaction amplification of cDNA demonstrated a deletion of the 54 bp of exon 6 from some of the alpha 2(I) mRNA. Analysis of genomic DNA from the patient revealed a single base change in one COL1A2 allele, substituting an A for a G as the first base of intron 6. This change mutates the obligate GT-dinulceotide splicing signal to AT and leads to exon skipping with splicing from exon 5 to exon 7. Loss of exon 6 sequences results in the loss of the procollagen-N-propeptidase cleavage site and a lysine residue that normally participates in covalent intermolecular crosslinking within collagen fibres.

The clinical features of a father and daughter with Ehlers-Danlos syndrome type VIIB are described. They included severe cutaneous fragility, generalized joint laxity, kyphoscoliosis and a slightly dysmorphic face in the adult, with generalized joint laxity and congenital hip dislocation, hyperextensible skin and easy bruising in the child. The dermis contained slightly distorted collagen fibrils when examined by electron microscopy. The disorder is caused by G to A point mutation in the first base of intervening sequence 6 with resultant mis-splicing.

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