Genetics in sport: Do single genetic differences impact sporting performance?

by Weaver • November 22, 2016 • No Comments

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genetics performance

One of the interesting variables in sporting performance is the influence genetics have on optimum performance. In this blog I wanted to look at the question that some commentators have posed that some athletes from certain parts of the world have an inherited advantage over others due to genetic markers. I decided to look at the research into some of the key single genetic markers noted to increase physiological performance and see if these questions are valid.

Introduction

The sporting accomplishments of distance runners and sprinters from African countries such as Kenya, Ethiopia and Jamaica are highly impressive. For example at the Beijing Olympics these countries accounted for 36 per cent of all track and field medals for men and women. With continued success noted for these countries at the London 2012 Olympics. These results have further enhanced the concept that certain racial groups have an inherent genetic advantage that heightens physiological performance levels. This is the controversial ideal that there is a black athletic supremacy. With the ideal emerging from over simplistic interpretations of performance along with the belief that skin color is linked to an individual’s genetic make-up (Cooper, 2004).

Early studies in this area reported small differences in sub-maximal work efficiency and endurance performance, which were attributed differences in mechanical efficiency (Boulay, et al., 1988). The authors concluded however, that there were no significant findings to support the concept of ethnic differences in work capacities and power output. Another early study supports biological differences between ethnic groups. Ama, et al. (1986) studied skeletal muscle characteristics of sedentary subjects with different racial backgrounds and noted that African students that descended from regions such as Cameroon and the Ivory Coast had 8 per cent lower type I and 6.7 per cent higher type IIa fibre proportions than whites. Additionally this sample had 30-40 per cent higher enzyme activity noted in phosphagenic and glycoltyic pathways.

Numerous studies have added to these findings looking more in depth into the physiological characteristics of black and white athletes focusing on comparative assessment. These have compared characteristics such as running economy, skeletal muscle composition, maximal aerobic capacity and lactate accumulation in black and white athletes. For example black athletes were noted as having lower lactate levels at exercise intensities (Weston, et al., 1999), higher functional capacity at race intensities (Weston, et al., 2000) and  better running economy (Weston, et al., 2000) when compared to their white counterparts.

These results contradict earlier findings that suggested black athletes were more genetically suited to shorter duration events (Ama, et al., 1986). Clearly this area of science is one within which it is difficult to make definitive conclusions. This has resulted from conflicting conclusions in studies that state the success of this racial group lays in short duration events, with other studies suggesting that it is longer duration events (Weston, et al., 2000). These findings show the difficulty that lay within grouping athletes under skin color and making conclusions about ethnic characteristics on the basis of small sample sizes.

The fact that many of the world’s best distance runners originate from certain regions of Kenya and Ethiopia rather than being evenly distributed across the countries further enhances the idea that certain ethnic groups possess inherent genetic disposition to perform in long distance events (Onywera, et al., 2006). A similar phenomenon is also seen in Jamaican sprinting with 80 per cent of national sprinters tracing their origins to the north-west region of the Jamaica (Robinson, 2007). Geographical differences in athlete production have been proposed to reflect a genetic similarity among those populating the regions for an athletic genotype and phenotype as a consequence of selection for a particular phenotype such as endurance or sprinting, if it offers an advantage in that environment. For example some believe that the Nandi tribe in Kenya has self-selected members for centuries based on endurance performance (Manners, 1997), therefore it is not surprising that there are postulations that Kenyan runners possess an “athletic gene” for distance running (Larsen, 2003). Similar postulations were made to explain superior African-American sprint performance, with these performers heritage laying in Western Africa. Theorists claim that these individuals have favorable physiological make-ups and that their pulmonary physiology, muscle fibre composition and metabolic pathways within their genetic make-up increase their performance levels (Morrison, & Cooper, 2006).

Morrison and Cooper (2006) hypothesize that biochemical differences between populations began and have continued over the last three centuries through natural selection. Cooper (2004) claimed that these differences began but did not end with the sickling of red blood cells. Cooper (2004) further advocated that individuals with the sickle cell trait possessed a significant advantage in the malarial African environment, with this trait triggering a number of physiological adaptations which had favorable consequences, within athletic performance (Morrison, & Cooper, 2006). While this hypothesis remains untested, another hypothesis to explain favorable West African biology may lay in the displacement process and harsh living conditions of slaves over the last number of centuries (Larsen, 2003). In these environments only the “fittest” slaves survived. Scott and Pitsiladis (2007) have stated that scientists who support the biological and genetic explanation for superior performance typically ignore the socio-economic and cultural factors which appear to explain the ethnic differences in performance. This review aims to explore the possible genetic explanations for differences in sports performances across ethnic groups

Genetic explanations for ethnic differences in sports performance

The ideal of an athletic superiority with a certain ethnic group is based on a preconception that the group constitutes a genetic homogeneous group defined by skin colour. This however is in contrast to findings that suggest there is more genetic variation among Africans than between Africans and Eurasians (Jobling, et al., 2004). Nevertheless the genetics of race is a controversial area of research and gives rise to a number of contrasting views. With some theorist supporting research into genetics as it can offer benefits in terms of diagnosis of disease and treatment (Burchard, et al., 2003). Other theorists are of the view that it should be abandoned for assessing the prevalence of disease genotypes (Cooper, et al., 2003).

The use of genetics as an explanation of sports performance is poorly understood and more difficult to study. Bejan et al. (2010) estimated that human genetic variation is shared by all humans and that marginal variation (<10%) is specific to major ethnic groups. This is backed up by the human genome project with analysis of haplotype (linked segments of genetic frequencies) frequencies showing that these are shared between two of the three geographical populations: Europe, Asia and Africa (International HapMap consortium, 2005). Therefore it is estimated that the level of genetic diversity between human populations is not significant enough to justify its use in terms of race (Jobling, et al., 2004). Therefore any biochemical, physiological and or anatomical differences between groups defined solely by skin color are not applicable to the source population. This is highlighted by Bejan et al. (2010) who referenced anthropometric data and showed that the centre of mass in black athletes was 3 per cent higher above the ground than in white athletes, with this equating to a 1.5 per cent speed advantage in swimming. These authors followed on stating that amongst male athletes of the same height Asians were more favoured than whites to perform in swimming events however their height is holding them back. Therefore it may be concluded that the process of comparison of physiological characteristics based solely on skin colour does not offer much insight in why some groups are successful in certain sports (Atkinson, et al., 2009). Below I have looked at some key genetic variables with regard to sprint and distance performance

Mitochondrial DNA (mtDNA) in distance and sprint athletes

Therefore there has been a push towards mapping the genetic ancestry of elite athletes. The first of these tests focused on uni-parentally inherited genetic markers such as mitochondrial DNA (mtDNA). This genetic marker provides a unique opportunity to explore the matriline of select groups as the marker is passes entirely matrilineally and accumulates mutations along the maternal genealogical line. Given the rapid mutation rate of mtDNA compared to the nuclear genome, it is possible to create detailed phylogenies to explore the matriline relatedness of people in addition to phenotypes of interest (Atkinson, et al., 2009). Grouping particular haplotypes creates easily comparable units of genealogical information with useful levels of predictability. When found in other parts of the world these haplotypes can be used as indicators of recent migration (Salas, et al., 2002).

This approach was applied to Ethiopian and Kenyan distance runners with results reveling that elite runners from Ethiopia and Kenya were not grouped to one area of the mitochondrial tree but results revealed a wide distribution, similar to their general population in contrast to the ideal that these athletes are a genetically distinct group defined by their mtDNA. As a result the mtDNA haplogroup diversity found in Ethiopian and Kenyan athletes does not support the role for an mtDNA polymorphisim as an explanation for their running success (Scott, et al., 2005). This finding further dismisses the hypothesis that the Ethiopian/Kenyan population from which the athletes are drawn, has remained genetically confined to East Africa, but instead shows that it has undergone migration and subsequent changes during the development of the human species. This rejects the common assumption that elite African distance runners have maintained and further developed the ancestral endurance phenotype through living in the East African highlands (Deason, et al., 2011).

Further analysis of specific population mtDNA halogroups in the Kenyan population and in Kenyan runners found that these are very different to their Ethiopian counterparts, with a lower frequency of haplogroups M and R noted in Kenyan population. These M and R haplogroups were noted as being present in 10 per cent of Kenyans compared to 45 per cent of Ethiopians (Scott, et al., 2009). It is interesting that these two regions which have has such success levels in distance running have such different ancestral contribution to their gene pool. In contrast to the Ethiopian cohort were no differences in mtDNA haplogroup distribution found between controls and international athletes. Athletes from Kenya displayed an excess of L0 haplogroups and a dearth of L3 haplogroups. Kenyan athletes also showed differences from control groups when each genetic sequence was compared to the sum of all others, showing an excess of M haplogroups. The association of mtDNA haplogroups L0 and M within Kenyan athletes may suggest that these haplogroups contain polymorphisms, which influence some aspect of endurance performance or its trainability but fail to explain the Kenyan running phenomenon (Mikami, et al., 2010).

Studies have also looked at the mtDNA haplogroup profiles of elite sprinters and controls, noting that there was difference in mtDNA profiles of elite sprinters from Finland compared to everyday controls (Niemi, & Majamaa, 2005). This research noted that there was no over representation of a particular haplogroup within sprinters when compared to the everyday population. Similarly significant associations between mitochondrial haplogroup G1 and elite endurance performance have been noted in elite Japanese athletes. This therefore could implicate mtDNA as a determinant of elite athletic status.

A more recent study compared the maternal linage of Jamaican and American elite sprinters. This study showed that these elite sprinters were found to be derived from similar source populations although there were differences seen within mtDNA haplotypes (Deason, et al., 2011). These associations of mtDNA haplogroups within elite sprinters would suggest that certain lineages contain markers for particular genotypes in both nuclear and mitochondrial genome types. With these genome types impacting on some aspect of sport performance, however these fail to explain the sprint dominance seen by athletes of West African descent such as Usain Bolt.

Y chromosome

The idea that elite African runners studied to date do not arise from a limited genetic isolate is further supported by the analysis of the Y chromosome haplogroup distribution of Ethiopian runners (Moran, et al., 2004). Ethiopian runners differ significantly in their Y chromosome distribution from both the general population and that of the Arsi region which a produces an excessive amount of elite runners (Moran, et al., 2004).

The finding that Y chromosome haplogroups were associated with athlete status in Ethiopians suggests that either an element of Y chromosome genetics is influencing athletic performance, or that the Y chromosome have been affected by population stratification. However the distribution of Y chromosome of the Arsi region did not differ from the rest of the Ethiopian population, therefore reducing the likelihood of this being caused from stratification of the population.

Recent published data found that the same haplogroups were over represented in a Kenyan cohort (Scott, et al., 2010) thus providing some evidence that the Y chromosome has a biological effect on running performance. However despite these findings results show similar levels of diversity to those found using mtDNA therefore collectively mtDNA and Y chromosome research findings fail to provide and genetic evidence to support the biology of ethnic differences in sports performance.

ACE Gene and Alpha-Actinin-3

Despite the postulation that certain ethnic groups are genetically adapted for athletic performance, only two candidate genes have been studied in East African athletes (Ash, et al., 2010) and in sprint athletes (Yang, et al., 2007; Scott, et al., 2010). The first of these was the angiotensin converting enzyme (ACE) gene. This gene is associated with a number of aspects of human performance (Jones, et al., 2002). In general the I allele has been associated with endurance performance and the D allele with power performance. With the I allele additionally associated with an increased tolerance at high altitude thus making it ideal for investigation. This is because there is a common assumption that these athletes life at high altitude accounts for their success.

As such both subsets of the ACE were tested in Kenyan runners (Scott, et al., 2005) and Ethiopian runners (Ash, et al., 2010). Results showed no significant differences in both I and D allele genotype frequencies between runners and controls. Although the controversy over the influence of ACE as a potential influencing factor on endurance performance continues, these studies did not show support for the role of ACE gene variation in explaining the running dominance of African athletes.

Only two genes (ACE and ACTN3) have been researched in elite sprint athletes. The alpha-actinin-3 gene (ACTN3) has been associated with elite physical performance in many studies (Yang, et al., 2003) and found at differing frequencies across populations (Mills, et al., 2001). One of the gene variants of ACNT3 has been linked with athlete status in Australian populations with the ACTN3-dificient XX genotype being present at a lower frequency in sprint and power athletes and at increased levels in endurance athletes (Yang, et al., 2003). This association has also been replicated in a number of Finnish cohort studies (Niemi, & Majamaa, 2005). Such studies have helped establish the link between this variant of ACTN3 (R577X) and muscular strength and sprint performance. Therefore it was surprising to see that this variant was absent in controls and sprinters from the USA and Jamaica (Scott, et al., 2010). With additional studies showing no link between this polymorphism and endurance performance in East African endurance runners (Yang, et al., 2007). These finding suggest that this polymorphism is not a major determining factor in African success within both sprinting and endurance events.

Conclusion

What has been seen is that the dominance of African athletes in both sprinting and endurance events has lead theorists to suggest that these athletes are genetically adapted to engage in competition within these events. However by genotyping key genes and genetic sequences it has been shown that these genes are not significant determinants of their success.

Whether or not nuclear variants can be attributed to these phenomenon remains to be shown. However the achievements of some populations in sporting arenas must rely on the integration of physiological, biochemical, psychological and biomechanical systems, which themselves can contribute a multitude of contributors. Therefore the likelihood that the success of these athletes is linked to a single polymorphism is unlikely. It is much more plausible to state that athletes rely on a combination of advantageous genotypes for increased performance levels. Research is currently looking a multiple polymorphisms and if there is a link between combined polymorphisms and increased athletic performance.

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