Orosomucoid polymorphism in Finns, Swedes and Swedish Saamis

Cancer among the Sami--a review on the Norwegian, Swedish and Finnish Sami populations

OBJECTIVES

The Sami are the Indigenous people of the northernmost parts of Sweden, Finland and Norway, and of the Kola Peninsula of Russia. The present review summarizes the main results from studies on cancer morbidity and mortality among the Sami and discusses these results in relation to exposure of known risk factors.

STUDY DESIGN

Literature review.

METHODS

A systematic search over the time period 1966-2008 for relevant articles was conducted on MEDLINE. Updates and recalculations of some of the results from the original data were also done.

RESULTS

Nine articles whose main focus is on cancer incidence or mortality among the Sami were identified. In all studies, the overall incidence of cancer or cancer mortality was lower among the Sami in comparison with the national populations. The differences were less striking in relation to regional reference populations, but the rates were still significantly lower for all populations of Sami, except for Swedish Sami women. Beyond the general trend of a lower cancer incidence among the Sami, there were some notable differences between the various Sami subpopulations.

CONCLUSIONS

The risk of developing and dying from cancer is low among the Sami. A life-style that includes cancer-protective factors, such as certain dietary components and physical activity, is the most likely explanation for the lower incidence of cancer among the Sami.

Cancer in the Sami population of Sweden in relation to lifestyle and genetic factors

The reindeer herding Sami of Sweden have low incidences of cancer. The aim of the present study was to investigate the cancer risk in a large cohort of Swedish Sami, containing Sami with different lifestyle and genetic Sami heritage. A cohort of 41,721 Sami identified in official national registers between 1960 and 1997, was divided into two sub-populations -- reindeer herding Sami (RS) and non-reindeer herding Sami (NRS). A demographically matched non-Sami reference population (NS) was used as standard when incidence and mortality ratios were calculated. Incidence and mortality data were obtained from the Swedish Cancer and Cause of Death Registers for the period 1961-2003. For Sami men, lower risks were found for cancers of the colon and prostate, and for malignant melanoma and non-Hodkins lymphoma, but higher for stomach cancer. The Sami women showed higher risks for cancers of the stomach and the ovaries, but lower risk for cancer of the bladder. The RS demonstrated lower relative cancer risks compared with the NRS. The lowest relative risk was found among the RS men, while the highest were observed among the NRS women. The RS men who had adopted a more westernized lifestyle showed a similar relative risk for prostate cancer as that of the NS living in the same region. Most of these differences in cancer risks could probably be ascribed to differences in lifestyle. It is concluded that the traditional Sami lifestyle contains elements, e.g. dietary contents and physical activity that may protect them from developing cancer.

Evaluation of the SNP tagging approach in an independent population sample--array-based SNP discovery in Sami

Significant efforts have been made to determine the correlation structure of common SNPs in the human genome. One method has been to identify the sets of tagSNPs that capture most of the genetic variation. Here, we evaluate the transferability of tagSNPs between populations using a population sample of Sami, the indigenous people of Scandinavia. Array-based SNP discovery in a 4.4 Mb region of 28 phased copies of chromosome 21 uncovered 5,132 segregating sites, 3,188 of which had a minimum minor allele frequency (mMAF) of 0.1. Due to the population structure and consequently high LD, the number of tagSNPs needed to capture all SNP variation in Sami is much lower than that for the HapMap populations. TagSNPs identified from the HapMap data perform only slightly better in the Sami than choosing tagSNPs at random from the same set of common SNPs. Surprisingly, tagSNPs defined from the HapMap data did not perform better than selecting the same number of SNPs at random from all SNPs discovered in Sami. Nearly half (46%) of the Sami SNPs with a mMAF of 0.1 are not present in the HapMap dataset. Among sites overlapping between Sami and HapMap populations, 18% are not tagged by the European American (CEU) HapMap tagSNPs, while 43% of the SNPs that are unique to Sami are not tagged by the CEU tagSNPs. These results point to serious limitations in the transferability of common tagSNPs to capture random sequence variation, even between closely related populations, such as CEU and Sami.

A recent genetic link between Sami and the Volga-Ural region of Russia

The genetic origin of the Sami is enigmatic and contributions from Continental Europe, Eastern Europe and Asia have been proposed. To address the evolutionary history of northern and southern Swedish Sami, we have studied their mtDNA haplogroup frequencies and complete mtDNA genome sequences. While the majority of mtDNA diversity in the northern Swedish, Norwegian and Finnish Sami is accounted for by haplogroups V and U5b1b1, the southern Swedish Sami have other haplogroups and a frequency distribution similar to that of the Continental European population. Stratification of the southern Sami on the basis of occupation indicates that this is the result of recent admixture with the Swedish population. The divergence time for the Sami haplogroup V sequences is 7600 YBP (years before present), and for U5b1b1, 5500 YBP amongst Sami and 6600 YBP amongst Sami and Finns. This suggests an arrival in the region soon after the retreat of the glacial ice, either by way of Continental Europe and/or the Volga-Ural region. Haplogroup Z is found at low frequency in the Sami and Northern Asian populations but is virtually absent in Europe. Several conserved substitutions group the Sami Z lineages strongly with those from Finland and the Volga-Ural region of Russia, but distinguish them from Northeast Asian representatives. This suggests that some Sami lineages shared a common ancestor with lineages from the Volga-Ural region as recently as 2700 years ago, indicative of a more recent contribution of people from the Volga-Ural region to the Sami population.

Cancer risk in the reindeer breeding Saami population of Sweden, 1961-1997

The Saami people are the natives of northern Scandinavia and the Kola Peninsula. In a cohort of 2033 Swedish reindeer breeding Saamis, the cancer risks between 1961 and 1997 were studied. In total, 193 cases of cancer were observed versus 322 expected in the general Swedish population and 249 in a geographically matched reference population of non-Saamis. In comparison to non-Saamis living in the same area, the reindeer breeding Saamis showed a statistically significant lower risk of developing cancer of the prostate and of malignant lymphoma, whereas the risk of stomach cancer was significantly higher. Although there were no statistically significant changes of cancer risks over time, temporal trends were indicated towards a decreased risk of cancer in the stomach and the prostate. The results suggest that the explanations of the low cancer risk of the reindeer breeding Saamis, in relation to the non-Saamis in the same environment, are to be found among lifestyle and/or genetic factors.