Prevalence of 845G>A HFE mutation in Slavic populations: an east-west linear gradient in South Slavs

Aim To compare A allele frequencies of the 845G>A mutation of 10 Slavic populations in central, eastern, and southern Europe between each other and with other European populations. Methods The 845G>A mutation from the DNA of 400 Polish neonates collected in 2005-2006 was analyzed by polymerase chain reaction-restriction fragment length polymorphism. The data were compared with reports from other countries. Results We identified 381 GG homozygotes, 18 GA heterozygotes, and 1 AA homozygote. The 845A allele frequency was 2.5%, which makes the summary figure for Poland from this and previous studies 3.5%. The average prevalence for Poland and other West Slavic countries was 3.6%, similar to Russia (inhabited by the East Slavs, 3.5%). The average prevalence in South Slavic countries was 2.2%, gradually decreasing from 3.6% in Slovenia to 0% in Bulgaria, with a longitudinal linear gradient (adjusted R2 = 0.976, P < 0.001). Conclusions The West and East Slavs, together with Finland, Estonia, Germany, Austria, Hungary, Slovenia, and Croatia, form a group with 845A allele frequencies between 3% and 4%. In the South Slavs, there is a gradual decline in the prevalence of 845A allele from northwest to southeast, with a surprisingly exact east-west linear gradient.

In 1996, two major HFE gene mutations (845G>A and 187C>G) responsible for an inherited form of hemochromatosis were identified (1). Hereditary hemochromatosis is a common autosomal recessive disorder characterized by increased iron absorption. It has significant clinical consequences such as liver cirrhosis, diabetes mellitus, arthropathy, cardiomyopathy, and endocrine dysfunction (2). A total of 60% to 96% of patients with hemochromatosis in Europe have the mutation 845G>A in exon 4. This causes cysteine to tyrosine substitution at position 282 (C282Y) of the polypeptide chain, resulting in destabilization of one of the bridging sulfide molecules disrupting HFE binding to β2-macroglobulin (1,3). The HFE polypeptide chain loses its ability to bind to transferrin receptor, and this results in a 200-300% increase in iron absorption from food. The severity of symptoms in homozygotes is variable and depends on the race, age, sex, and diet (2, 4,5). Merryweather-Clarke et al (6) reported the highest prevalence of 845A HFE in northwestern Europe (5.2 to 10.1%), ie, Sweden, Norway, UK, and Ireland. In Finland, Hungary, Poland, Russia, Austria, Germany, Czech Republic, and Slovakia the prevalence was between 3.2 and 4%. In southern Europe (Greece, Romania, Italy, and Spain), the prevalence is very low (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) and in Turkey it is almost non-existent (7). According to more recent data, France (6.1%) can now be added to the northwestern group (19,20). As the major comparison of the prevalence between European countries by Merryweather-Clarke et al (6) included few data on Slavic populations, we further assessed the 845A HFE frequency in the Polish population and compared it with other Slavic populations and previously published results, as well as determined its distribution across the entire Europe.

MAteriAlS And MethodS
The study sample comprised 400 consecutively born neonates (187 female and  The average prevalence of 845A allele in the countries inhabited by the West Slavs was 3.6% and varied from 3.5% in Poland (including our study) through 3.8% in the Czech Republic to 4.0% in Slovakia (10,14,21-23) (Figure 1). This places the West Slavs to a group with allele frequencies between 3% and 4%, together with East Slavic Russia (3.5%) and Finland, Estonia, Germany, Austria, Hungary, Slovenia, and Croatia.

diSCuSSion
Our study showed that the distribution of 845A HFE among Slavic countries was bi-modal. The West and East Slavs had a similar prevalence as other central and eastern European populations, with values ranging between 3% and 4%. The South Slavs exhibited a linear decreasing west-to-east trend, with a prevalence varying from 3.6% to 0%.
Population migrations in Europe have led to the distribution of ethnic groups and cultures, and consequently to genetic mixing (68). Migrations, together with other factors, have also determined the prevalence of genetic diseases, such as hemochromatosis (68). Initially, the mutation 845G>A HFE was described in populations of northwestern European origin and has spread to territories inhabited by the Celts (68). On the other Our study, together with the study by Merryweather-Clarke et al (6), suggests that a group of countries in central and east Europe have similar prevalence of the mutation. To our knowledge, this is the first comprehensive comparison of the 845A HFE mutation prevalence between all West and South Slavic populations.
Among the South Slavs, there was a linear gradual decrease in the prevalence of allele 845A HFE. This linearity suggests a possible stability and demic diffusion of the genes from the northwest into a block (the South Slavs) in which there are no conditions for the maintenance of a high frequency of the mutation (either because of genetic background or environmental reasons). An alternative explanation is that there is a gradient of conditions to which South Slavic populations have been exposed, forming a gradient of positive selection and heterozygous advantage. A third possibility, perhaps supported by Y-chromosome haplotypes, is that the medieval expansion of the Slavs (beginning during the 5th and 6th century) resulted in a gradient of ancestors carrying this allele (69).
It would be interesting to see if such a gradient is found with mutations in other genes and to compare this with genetic distance data both among the Southern Slavs and the surrounding populations. Additionally, a spatial frequency distribution map constructed using intra-country regions would be of benefit -especially as a gradient similar to the one described here (but across one country) has been found in Portugal (57). It would also be interesting to fill in the gaps for the East Slavic populations, including those in Belarus, Ukraine, and the West Slavic group in Germany (the Sorbs). declaration of authorship GA gave the idea for the study and primarily conducted the research. JSC was involved in the analysis, gave the ideas, and participated in writing of the manuscript. BL was involved in the selection of Polish origin newborns and collection of cord blood samples. AC was involved in the analysis, gave the ideas, and participated in writing of the manuscript.