Inbreeding levels in Northeast Brazil: strategies for the prospecting of new genetic disorders

Silvana Santos,Francisco Rennan Lopes De Paiva,Fernando Kok,Mathias Weller,Paulo A Otto

doi:10.1590/s1415-47572010005000020

Abstract

A new autosomal recessive genetic condition, the SPOAN syndrome (an acronym for spastic paraplegia, optic atrophy and neuropathy syndrome), was recently discovered in an isolated region of the State of Rio Grande do Norte in Northeast Brazil, in a population that was identified by the IBGE (Brazilian Institute of Geography and Statistics) as belonging to the Brazilian communities with the highest rates of “deficiencies” (Neri, 2003), a term used to describe diseases, malformations, and handicaps in general. This prompted us to conduct a study of consanguinity levels in five of its municipal districts by directly interviewing their inhabitants. Information on 7,639 couples (corresponding to about 40% of the whole population of the studied districts) was obtained. The research disclosed the existence of very high frequencies of consanguineous marriages, which varied from about 9% to 32%, suggesting the presence of a direct association between genetic diseases such as the SPOAN syndrome, genetic drift and inbreeding levels. This fact calls for the introduction of educational programs for the local populations, as well as for further studies aiming to identify and characterize other genetic conditions. Epidemiological strategies developed to collect inbreeding data, with the collaboration of health systems available in the region, might be very successful in the prospecting of genetic disorders.

Highlights

In the 1950’s and 1960’s, Freire-Maia and his collaborators, as well as other authors, conducted a number of studies on inbreeding levels of Brazilian populations
The study was developed with the participation of agencies involved in programs for the training of health agents [“Programa de Agentes Comunitários de Saude (PACS)”] and for promoting family health [“Programa de Saúde da Família (PSF)”], in five municipal districts of the state of Rio Grande do Norte (São Miguel, Pilões, Riacho de Santana, Serrinha dos Pintos, and Olho d’Água do Borges), all of them recently identified by IBGE as belonging to the 50 Brazilian communities with the highest rates of “deficiencies” (Neri, 2003)
In Serrinha dos Pintos, more than 30% of all couples were constituted by related individuals (F = 0.0095), a fact that can be explained by the relative geographic isolation of its population, living in a highland region in the western part of the state of Rio Grande do Norte

Summary

Introduction

In the 1950’s and 1960’s, Freire-Maia and his collaborators, as well as other authors, conducted a number of studies on inbreeding levels of Brazilian populations. The overall mean value of the frequency of consanguineous marriages in Brazil was estimated to be 4.8%, corresponding to an average inbreeding coefficient F = 0.0023. The lowest inbreeding levels were detected in the southern states, whereas in some states of Northeast Brazil these rates varied from 6% to 12% (Freire-Maia, 1957, 1958; Freire-Maia and Freire-Maia, 1961; see Salzano and Freire-Maia, 1967; Freire-Maia, 1968, 1989, 1990, for summaries and updates of these studies). Since most of the affected subjects were inbred, we became interested in evaluating the consanguinity rates in the region, and in developing a project to study the consequences of these rates on morbidity

Methods

Results

Conclusion