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Finding Genes Controlling Complex Phenotypes

Finding Genes Controlling Complex Phenotypes. Elaine Ostrander, PhD National Human Genome Research Institute National Institutes of Health. Methodology and Approaches. Whole Genome Association Studies Human Height Obesity Behavior Others Animal Models Skin Color Skeletal Size

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Finding Genes Controlling Complex Phenotypes

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  1. Finding Genes Controlling Complex Phenotypes Elaine Ostrander, PhD National Human Genome Research Institute National Institutes of Health

  2. Methodology and Approaches • Whole Genome Association Studies • Human Height • Obesity • Behavior • Others • Animal Models • Skin Color • Skeletal Size • Leg length • Racing Speed

  3. WGA Association Studies Associated with Height • GWA scan data • Multiple SNPs in strong LD with each other reached genome wide levels of significance • Mice with with homozygous deletions at this locus are short in stature

  4. Genetics of Obesity • In whole genome association studies encompassing over 38,000 subjects, common set of variants in FTO gene were found to be associated with increased BMI. • Result grew out of study of diabetes and represents increased risk for both disease and obesity. • No mechanistic data. Appears that risk is mediated through changes in fat mass. • 16% of adults who are homozygous for the risk allele weigh 3 Kg more and had 1.67 fold increased risk of obesity than those without risk allele. Frayling et al., (2007). Science April 12

  5. Implications for Society are Enormous Societal traits perceived to be advantageous or desirable: tall and thin • Discrimination--obesity predisposes to variety of health problems diabetes, heart disease, blood pressure, etc. • Sports--Preselection and training of individuals • Taller: basketball, volleyball • Shorter: jockey, ice skater, gymnastics • Thinner: runner, dancer

  6. Genetics of Skin Color

  7. Genetics of Skin Color wt • golden gene (SLC24A5 in humans) encodes a cation exchanger that localizes to the melanosome or its precursor. • Protein product affects pigmentation in both zebrafish and humans • Melanophores of golden mutations are smaller, more pale, more transparent, and contain fewer melanosomes gol gol wt Lamason et al., (2005) Science 310:1782-1786

  8. Region of decreased heterozygosity in Europeans at SLC24A5 gene • Conservation of ancestral allele predominates • in African and East Asian populations. • Variant allele is nearly fixed in European populations correlating with lighter skin.. • Study suggest that SLC24A5 explains 25-38% of the European-African difference in skin melanin index. Lamason et al., (2005) Science 310, 1782 -1786

  9. Mapping Variation in the Canine System • Each breed fixed for specific traits • Creation of breeds recent and rapid • Small number of genes responsible for many complex traits Sutter et al., (2007) Science 316:112-5

  10. IGF1 Strong Statistical Association With Skeletal Size In Portuguese Water Dogs

  11. Identical Selective Sweep Across IGF1 in 14 Small Dog Breeds

  12. Mapping Breed-Fixed Morphology Force vs. speed axis of variation Achondroplasia Herding behavior Brachycephaly Body size

  13. Performance Enhancing Polymorphisms: Genes Controlling Racing Speed In Dogs Mosher et al., (2007) PLoS Genetics (in press)

  14. Muscle Mass Controlled in Part by Levels of Myostatin • “Bully” whippets appear similar to other species with “double muscle” phenotype. • Phenotype caused by two copies of a 2 bp deletion in exon 3 removes the latter 17% of the protein disrupts structure Belgian Blue Cattle Bully Whippet

  15. Dogs Heterozygous for the MSTN Deletion Show an Intermediate Phenotype

  16. P ≈ 7.43 x 10-6 ; Kruskal-Wallis Test P = 3.47 x 10-5; Kruskal-Wallis test P = 0.0015; Kruskal-Wallis test Mh mutation explains 60% of the variation in measurements

  17. Could this increased musculature affect a dog’s speed?

  18. Fisher’s Exact Test: A vs B,C,D P=0.00027 AB vs CD P=0.00073 A vs B P=0.086 C vs D P=0.42 Kendall’s NP P ~ 0.000283 MSTN Deletion is Overrepresented in Grade A Racers

  19. MSTN in Athletics • Are similar mutations found in other competitive or high performing groups? • What other performance-enhancing polymorphisms remain to be found? Many? • Vital area of research for both humans and animals • Little is known about risks and side effects Vogel. Science (2004) Sweeney. Sci. Am. (2004)

  20. Genetics of Behavior ? ? • Dozens of putative loci identified for behavioral disorders and many others • Bipolar disorder, Schizophrenia • Autism • ADD and ADHD • Etc. • Ongoing canine studies for: • “Rage” in English Spring Spaniels • Obsessive Compulsive Disorder in Bull Terriers • Naturally occurring behaviors such as prey drive, herding, learning, etc. ?

  21. Summary • The question of Nature versus Nurture remains, except now we know a great deal more about the “nature” part. • Will this knowledge affect our collective behaviors? • Will we as a society and as individuals continue to view ourselves as full of potential? • Or will our genetic profiles make us self-limiting? • Next inroads must be into genetic loci affect our ability to rise above our “genetic mandates”

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