Correlation between consanguineous marriages and age-standardized mortality rate due to breast cancer, an ecologic study

Abstract

To the editor Consanguineous unions are common in several countries. This is associated with increase levels of morbidity and mortality in offspring [1–4]. Some studies have shown that consanguinity increased some adverse effects at population level [5–7]. Susceptibility to cancer in offspring of consanguineous marriages has been studied [8–13]. Parental consanguinity is linked to a decreased risk of breast cancer [13]. Other studies, however, have shown that consanguinity does not affect the susceptibility to breast cancer [10–12]. For countries such as our country, where the consanguineous marriage is common [14, 15], the association between consanguinity and mortality due to cancers is highly important for public health programs. To the best of our knowledge, there is no study concerning the association between consanguinity and mortality rate due to breast cancer. Therefore, the present ecological study was done. Since cancers are common in older age groups, a population that is older will have a higher crude cancer incidence rate. Age standardization is a procedure where weighted averages of age-specific rates are used to modify rates to a standard population to minimize the effects of differences in the age composition of given populations when comparing rates for these populations. The purpose of this rate is to compare groups of people from different backgrounds and age structures. Data about age-standardized mortality rates (ASMR) due to breast cancer (per 100,000 population) (for 2002) and gross national income per capita (GNI; at international dollars) (for 2000) were obtained from the World Health Organization web site ( http://www.who.int). Inbreeding coefficient is the probability that an individual has received both alleles of a pair from an identical ancestral. The mean of inbreeding coefficient (a) values for the countries was obtained from the web site http://www. consang.net. Selection of countries was based on availability of all above mentioned variables. Table 1 shows the list of 62 selected countries and the values of the corresponding variables. Logarithmic transformation was used on GNI per capita and a, because they had highly skewed distributions and the logarithmic transformations brought them closer to the normal distributions. Partial correlation analysis was carried out to eliminate the possible confounding effect of GNI per capita on the correlation of ASMR due to breast cancer with the mean inbreeding coefficients. After controlling for log10GNI per capita, significant negative correlation between log10a and the ASMR due to breast cancer was observed (r = -0.267, df = 59, P = 0.038). We noted a possible lack of reliable data from lowincome countries. Therefore, we stratified the countries according to their GNI per capita, lowand high-income countries with GNI per capita less than and more than $10,000, respectively. Statistical analysis showed that in high-income countries, after controlling for log10GNI per capita, correlation between ASMR due to breast cancer and log10a was significant yet (r = -0.782, df = 20, P \ 0.001). It might be concluded that consanguinity influences ASMR due to breast cancer independent of country income. Several studies showed higher mortality rates of neonatal, infant, and under 5-year mortalities in consanguineous marriages [1, 2, 7]. Taken together, the negative M. Saadat (&) I. Saadat Department of Biology, College of Sciences, Shiraz University, 71454 Shiraz, Iran e-mail: saadat@susc.ac.ir; msaadat41@yahoo.com