Geographic heterogeneity of 4 common worldwide cystic fibrosis non-DF508 mutations in Brazil.

Cystic fibrosis (CF) is an autosomal recessive disease caused by at least 750 different mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The frequency of the most common mutation (DF508) in Brazilian patients of European origin is 47%. To determine the frequency of 4 other common CF mutations (G542X, G551D, R553X, and N1303K) in Brazilian patients of European origin, we used direct polymerase chain reaction (PCR) amplification of DNA obtained from dried blood spots on Guthrie cards. The DNA came from 247 non-DF508 chromosomes from 172 Brazilian CF patients ascertained from 5 different states of Brazil. The results show that the 4 mutations account for 17% of the non-DF508 alleles and only 9% of the total number of Brazilian CF alleles. Overall, the frequency of each mutation is different from northern European and North American populations but similar to southern European populations, mainly the Italian and Spanish populations. When Brazilian patients of European origin are grouped according to state of birth, the frequencies of the mutations are significantly different between southern and southeastern states of Brazil. Therefore there are serious implication for risk assessment of DNA-based tests in heterogeneous populations such as Brazilians. Further studies are needed to identify the remaining 44% of CF mutations for the different populations and regions of Brazil.

Cystic fibrosis in the Brazilian population: DF508 mutation and KM-19/XV-2C haplotype distribution.

We have used PCR amplification of DNA obtained from Guthrie cards to identify the DF508 mutation and correlate it with the allele frequencies at two polymorphic loci (XV-2C and KM-19) closely linked to the cystic fibrosis gene. The DNA came from 193 white Brazilian families affected by cystic fibrosis and living in five different states of Brazil. The distribution of the haplotypes derived from the DF508 and non-DF508 XV-2C/KM-19 genotypes indicates that 88% of the DF508 alleles are linked to haplotype B and suggests that high heterogeneity exists among the non-DF508 cystic fibrosis alleles occurring in different states. Our data can be used to compare linkage disequilibrium between Brazilians and other heterogeneous populations where the DF508 mutation frequency is low and where many different rare mutations account for the remaining recessive cystic fibrosis alleles.

Regional distribution of cystic fibrosis-linked DNA haplotypes in Brazil: multicenter study.

The restriction fragment length polymorphism (RFLP) haplotypes of cystic fibrosis (CF) alleles vary between populations. To determine the distribution of two RFLPs (XV-2C and KM-19) that are tightly linked to the CF locus, we analyzed a white sample from five different states of Brazil. The haplotypes of 314 CF- and 237 non-CF-bearing chromosomes were uniformly distributed over the five states. The XV-2C allele and haplotype frequencies and the degree of linkage disequilibrium were determined. These were similar to values previously reported in southern European countries but different from results reported for northern and central Europe and North America. In contrast, although KM-19 allele frequencies differed between Brazilian states and European and North American countries, these frequencies were similar to values reported in black Americans. A significant proportion of Brazilian CF-bearing chromosomes had less common haplotypes, suggesting a heterogeneous distribution of CF gene mutations among Brazilians. Further studies are needed to identify the mutations affecting the Brazilian CF patients with various haplotypes.

DNA analysis of cystic fibrosis in Brazil by direct PCR amplification from Guthrie cards.

A 3 bp deletion of codon 508 (phenylalanine) of the cystic fibrosis (CF) gene constitutes the mutation of most CF chromosomes. The frequency of this mutation (referred to as delta F508), varies considerably between populations, ranging from 26% of the CF mutations in Turkey to 88% in Denmark. To determine the frequency of the delta F508 mutation in Brazilian Caucasoid CF patients, we used direct polymerase chain reaction (PCR) amplification of DNA obtained from dried blood spots on Guthrie cards, followed by ethidium bromide staining of gels. Although the overall frequency of the delta F508 mutation was 47% of 380 CF chromosomes from Brazilian Caucasoids born in five different states, significant interstate differences were observed, ranging from a delta F508 frequency of 27% to 53%. While our method could be used to screen patients and their relatives for carrier testing and prenatal diagnosis, the efficacy of screening only for the delta F508 mutation would be low, and would vary from state to state. Screening for a panel of local mutations will be needed to increase the mutation detection rate and optimize genetic counseling.