ABSTRACT
Fatal familial insomnia (FFI) and familial Creutzfeldt-Jakob disease (fCJD) are familial prion diseases with autosomal dominant inheritance of the D178N mutation. FFI has been reported in at least 27 pedigrees around the world. Twelve apparently unrelated FFI and fCJD pedigrees with the characteristic D178N mutation have been reported in the Prion Diseases Registry of the Basque Country since 1993. The high incidence of familial prion diseases in this region may reflect a unique ancestral origin of the chromosome carrying this mutation. In order to investigate this putative founder effect, we developed "happy typing", a new approach to the happy mapping method, which consists of the physical isolation of large haploid genomic DNA fragments and their analysis by the Polymerase Chain Reaction in order to perform haplotypic analysis instead of pedigree analysis. Six novel microsatellite markers, located in a 150-kb genomic segment flanking the PRNP gene were characterized for typing haploid DNA fragments of 285 kb in size. A common haplotype was found in patients from the Basque region, strongly suggesting a founder effect. We propose that "happy typing" constitutes an efficient method for determining disease-associated haplotypes, since the analysis of a single affected individual per pedigree should provide sufficient evidence.
Subject(s)
Amyloid/genetics , Creutzfeldt-Jakob Syndrome/genetics , Founder Effect , Insomnia, Fatal Familial/genetics , Protein Precursors/genetics , Registries/statistics & numerical data , DNA Damage , Genetics, Population , Genotype , Haplotypes , Humans , Inheritance Patterns , Polymerase Chain Reaction , Prion Proteins , Prions , SpainABSTRACT
In 1995, a surveillance system for prion diseases was set up in the Basque Country, an autonomous region in northern Spain (2.1 million inhabitants). In the period from January 1993 to December 2003, we diagnosed 21 patients with familial prion diseases prospectively and another 4 patients retrospectively. They represent 35% of all the cases referred to the epidemiological registry. Two main possible explanations for this unusual high incidence of familial prion diseases are proposed: first, comprehensive case ascertainment by public health neurologists; second, a probable cluster of the D178N mutation within families of Basque origin related to a still unconfirmed common ancestor. Further genetic and genealogical studies should resolve this issue.
