Dysplastic nevi. Occurrence in first- and second-degree relatives of patients with 'sporadic' dysplastic nevus syndrome.

In this study a cross-sectional survey was undertaken among 156 living family members of 31 probands originally classified as having sporadic (histologically verified) dysplastic nevus syndrome (DNS). Seven (13.2%) of 53 parents had clinically recognizable DNS. Twenty-six (36.1%) of the 72 sibs showed dysplastic nevi. The diagnosis of DNS in family members was based on mainly clinical examination; in eight family members--those with only mild manifestation of DNS--a nevus was removed for histologic confirmation. After correction for pedigree size, we found that 60% of patients with "type A sporadic" DNS actually had one or more relatives with a DNS phenotype. Only 25% (8/30) of the probands were ultimately true sporadic cases without a DNS-affected first- or second-degree relative. In 15% (5/31) of the probands no conclusions concerning the type of DNS could be made because the pedigree size did not allow such a conclusion. We also found a higher prevalence of dysplastic nevi among the younger generation as compared with the older generation in our probands with DNS and their families as well as in a general population study of 400 individuals. This generation-dependent difference in expression of the DNS phenotype suggests that besides a genetic factor, other factors may play a role in the development of the characteristic phenotype.