Behavioral Genetics DB

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GENETICS OF ATHLETIC PERFORMANCE

Dr. Katie Dabrowski, PT, DPT

Some beginning concepts

  • Darwin’s theory of natural selection = individuals with traits that are favorable are more likely to survive and reproduce.
  • Those who are “stronger” are better equipped to handle struggles of the world
  • Each individual has a limited capacity to perform exercise – but what determines the limit to that capacity?
  • It is proposed that up to 50% of physical fitness is due to genetics
  • Athletes may be inherently predisposed to be more fit
  • But there may be a trade-off – genetically skilled athletes in one domain may be lesser-than in another domain (a sprinter with power and strength vs. lacking endurance, for example)
  • What genes are responsible for an athlete dominating in one sport (let’s say a sprint) rather than another (like a marathon)?

Components of Performance

  • Body morphology: Height and body composition
  • Aerobic endurance: Ability to sustain an aerobic effort over time.
  • Requires the ability of the cardiovascular system to deliver oxygen to working muscles, and the ability of those muscles to utilize that oxygen
  • Quantified via VO2max, but other factors like economy and ventilatory threshold influence performance in addition to VO2max
  • Muscular strength: Ability of muscle to generate force.
  • Quantified via one rep max
  • Cognitive factors
  • Injury susceptibility
  • Nutrition
  • Trainability

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Performance Enhancing Polymorphisms (PEPs)

  • PEPs = Genetic variants that, when inherited, can lead to improved athletic performance
  • 200+ PEPs exist

Angiotensin-Converting Enzyme

  • ACE gene contains the first PEP to be identified
  • ACE catalyzes the conversion of angiotensin I into angiotensin II, which affects vasoconstriction and regulation of salt and water homeostasis via releasing aldosterone
  • ACE is also responsible for regulating inflammatory reactions to lung injury, respiratory drive, erythropoiesis, tissue oxygenation, and regulation of skeletal muscle efficiency

Angiotensin-Converting Enzyme

  • Most common polymorphism associated with ACE is of the I allele
  • This polymorphism is associated with improved performance in endurance sports due to higher circulating and tissue ACE activity
  • ACE polymorphisms and athletic performance were first studied in Australian National Rowers at the pre-Olympic trials in 1996
  • Researchers found significantly increased frequency of I allele in elite rowers compared to normal controls
  • Another study investigated the role of ACE polymorphisms on body composition by training men over a 10-week period
  • Individuals with the I genotype had a greater anabolic response
  • And another study found a relationship between the I allele and mountaineering – individuals who engage in high altitude mountaineering ascending over 8000 meters without supplemental oxygen show an excess in the ACE I allele frequency

ACTN3 R577X

  • This gene codes for an important protein found exclusively in the fast type II muscle fibers used during explosive activities
  • A polymorphism resulting in a premature stop codon (X) rather than (R) at position 577
  • The R allele is advantageous in power events, and the RR genotype is overrepresented in elite power athletes; the X polymorphism is associated with lower sprinting ability and muscle strength
  • A study of elite European athletes found that power athletes are 50% less likely to have the XX genotype

NRF1

  • NRF1 has a role in mitochondrial biogenesis, oxidative phosphorylation, and increased capacity for energy during exercise
  • A study of Chinese men found two SNPs (single nucleotide polymorphisms) in noncoding regions of NRF1 that were associated with submaximum aerobic capacity (ventilatory threshold)
  • These men underwent a strenuous endurance program for 18 weeks of running, swimming, and cycling
  • Those without the two SNPs developed significantly better ventilatory thresholds compared to those with the polymorphisms

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ADRB2

  • A study of elite male endurance athletes reported a significant difference in a SNP in the ADRB2 gene
  • Sedentary controls had an excess of the Gly allele compared to these elite athletes
  • Gly allele is associated with increased body mass index (BMI)

Mitochondrial DNA

  • Endurance athletes tend to have enhanced mitochondrial function:
  • Increased mitochondrial gene expression
  • Increased mitochondrial DNA
  • Increased mitochondrial enzyme activity
  • Mitochondrial function is linked to aerobic fitness and insulin sensitivity

Nitric oxide synthase

  • At rest, increased nitric oxide (NO) production and NO synthase (NOS) inhibition can increase and decrease, respectively, blood flow to skeletal muscle
  • NO decreases mitochondrial respiration
  • NOS inhibition blocks glucose transport during exercise; NO has the opposite effect
  • NOS3, a polymorphism, is linked to increased adaptability of the heart during exercise

Myostatin

  • MSTN gene gained interest when a 4-year-old German boy who was homozygous for MTSN mutations and displayed significant muscle hypertrophy
  • He was shown to have very muscular thighs and upper arms at birth
  • Ultrasonography showed that his quadriceps muscle was 7.2 SD above the mean
  • His mother was a former Olympic sprint swimmer and was heterozygous for the same mutation

PPARD

  • PPARD (peroxisome proliferator-activated receptor-delta) gene = determinants of mitochondrial function
  • PPARD:
  • Regulates the gene expression in lipid and carbohydrate metabolism
  • Affects insulin sensitivity by modifying skeletal muscle glucose uptake
  • Polymorphisms in this gene are associated with predisposition to endurance performance
  • Frequency of PPARD polymorphism in endurance athletes = significantly higher than controls

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PGC-1

  • PGC-1 regulates the expression of genes for oxidative phosphorylation and ATP production
  • Muscle-specific expression of PGC-1 improves performance during voluntary and forced exercise challenges
  • PGC-1 transgenic mice have enhanced performance during peak VO2 tests

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HIFs

  • HIFs = hypoxia inducible factors (proteins)
  • Help us to understand the body’s response to hypoxia in tissues during increased oxygen demand (muscles working at high intensities)
  • The genes controlled by HIFs include those that:
  • Stimulate red blood cell production*
  • Encode glycolytic enzymes*
  • *These things are critical for achieving high levels of anaerobic performance
  • Removing HIF causes an adaptive response in skeletal muscle similar to endurance training – aka these muscles are no longer able to be powerful and anaerobic with short bursts, but instead perform best with endurance activities

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Injury Risk

  • Resistance to and/or the ability to recover from injury is another integral factor for optimal performance
  • Two main areas studied for genetic links to injury:
  • Concussion
  • Tendinopathy

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Concussion

  • APOE is the gene most frequently studied with regard to concussion/mild TBI
  • It has three isoforms (ε2, ε3, and ε4 alleles), and the ε4 allele has a strong association with Alzheimer’s disease
  • This association led to many researchers investigating a possible link between this allele and risk for concussion/outcomes after TBI
  • Some studies have found that individuals with the ε4 allele suffer worse outcomes from head injury; boxers with the ε4 allele have higher chronic brain injury scores

Tendinopathy

  • Tendinopathy = pain and pathology associated with overuse in/around tendons
  • Several genes associated with tendon injuries
  • COL1A1
  • COL5A1
  • COL12A1
  • COL14A1
  • TNC
  • MMP3
  • TGFB1
  • GDF-5
  • We’ll highlight some of them

COL1A1

  • Collagen type I alpha 1 gene
  • Collagen type I fibrils are a major constituent of bone matrix, forming strong parallel bundles of fibers in tendons and ligaments
  • A SNP polymorphism of COL1A1 which results in a T to G substitution is associated with osteoporotic fracture, osteoarthritis, myocardial infarction, lumbar disc disease, and stress urinary incontinence
  • TT genotype = reduced risk of cruciate ligament ruptures and shoulder dislocation ruptures compared with GG genotype

TNC

  • Tenascin C gene
  • Association of ABO blood group with Achilles tendon injury
  • O blood = more susceptible to tendon injuries
  • TNC gene is closely linked to the ABO gene that determines blood type