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Origin of Foot Deformity

Discussion in 'General Issues and Discussion Forum' started by sandra.jones, Mar 30, 2009.

  1. sandra.jones

    sandra.jones Member


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    Do we know to what extent foot deformity is developmental, environmental, or neuropathic ( thinking of diabetes here) in origin?

    Sandra
     
  2. drsarbes

    drsarbes Well-Known Member

    Hi Sanda:

    Your question seems a bit too generalized, can you be more specific?
    What foot deformity are you referring to (in diabetics)?

    There are a few to choose from!
     
  3. Heritability can be estimated for any quantitative character within populations, for example: the angle of abduction of the hallux on it's metatarsal. This provides information regarding the genetic versus environmental components of the character under examination. The problem is that heritability is not a fixed number and will vary with time and population. Within my PhD I looked at hallux valgus and a number of other foot related variables in this way.

    More on heritability here:http://en.wikipedia.org/wiki/Heritability
    Article on heritability in diabetes here: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1674860
     
    Last edited: Mar 30, 2009
  4. drsarbes

    drsarbes Well-Known Member

    Hi Simon:
    When you say heritability is not a fixed number, are you relating this to Hallux Abductus angle?

    As you are aware, like anything else, if you collected enough data you could correlate maternal and paternal HAA to offspring HAA, at a given age. It might be an interpretive leap to relate the two, but I've seen statistical gymnastics before!

    Steve
     
  5. Not just to HAA, heritability per se is not constant. The parent-offspring regression is what I did as part of my PhD, this is a common approach employed in quantitative genetics. I also age adjusted the data as age is an important co-variable.
     
  6. drsarbes

    drsarbes Well-Known Member

    " heritability per se is not constant"

    Interesting. Wouldn't it depend on what level you are examining for inheritance?

    I'm not fluent in genetics, but from what I recall, a gene (or series of or part of) is either in the genetic code of an individual or it is not. If you are testing at this level it would be a matter of YES or NO, wouldn't it?

    If you are examining phenotypes and trying to relate it to a genetic code plus other environmental factors, if you could, in fact (and I'm not saying that one could) measure all the influencing factors you might come up with a constant.
    The only thing that is keeping a researcher from being successful is our own limitations on quantifying all the factors that do affect the final phenotype.

    Does this make sense to you, Simon, or am I way off base?

    Steve (the non scientist)
     
  7. Steve, I'm trying to stay with you here;) It is important to realize that the heritability is a property not only of the character but also of the population; of the environmental circumstance to which the individuals are subjected, and of the way in which the phenotype is measured. Since the value of the heritability depends on the magnitude of all components of variance, a change in any one of these will affect it (for example, if you measure HAA in a population, and I measure HAA in the same population the heritability will be slightly different due to the differences in our measurements due to inter-tester measurement error/ between day variation etc.). All the genetic components are influenced by gene frequencies and may therefore differ from one population to another, according to past history of the population. In particular, small populations maintained for long enough for an appreciable amount of fixation to have taken place are expected to show lower heritabilities than larger populations. The environmental variance is dependent on the conditions of culture: more variable conditions reduce the heritability; more uniform conditions increase it (all subjects wearing the same shoes, or a wide variety of shoes, measure me today, then measure me in 5 years time when I've had five years of different environmental influence. The example I used to use here is this, if we measured the length of my nose from its base above my top lip to its tip today and then my nose was hit by an environmental influence such as a brick, the phenotypic value could well be different tomorrow :D). And, finally, if the phenotype is the mean of two or more measurements the heritability will differ from that of a single measurement. So whenever a value is stated for the heritability of a given character it must be understood to refer to a particular population under particular conditions. Values found in other populations under other circumstances will be more or less the same according to whether the structure of the population and the environmental conditions are more or less alike.

    Hope this helps. I can give you more, but I'll have to dig out my quantitative genetics texts.
     
  8. drsarbes

    drsarbes Well-Known Member

    OK Simon, I get it now. Thanks for taking the time to explain this.
    ( the brick hitting your nose really helped)

    Getting back to Sandra's original post, even if she were to give a very specific pathology the best we could do is design a study that would give us a mean influence (as a percent) of the various factors affecting this pathology in a given (well) defined population and at a given point in time.

    Right?

    Steve
     
  9. Right. We are basically partitioning the variance. In the case of heritability this is into genetic and environmental components. It's a pretty blunt tool, but has been widely used. You could also partition the variance by building multiple regression models employing other predictors and in so doing identify the independent variables that "explain" the variance in our specific (dependent) pathology. We can use models like this to predict the risk that an individual might have of developing said pathology, within the statistical limits of the model. This is a somewhat brighter tool. :drinks
     
  10. sandra.jones

    sandra.jones Member

    My question arose from considering a group of children /adolescents with diabetes, biomechanical screening, diabetes foot screening and (some) discussion around footwear. And your discussion has elicited further thoughts which will take me down another route.

    Thank you.

    S
     
  11. drsarbes

    drsarbes Well-Known Member

    Hi Sandra:

    Simon can correct me if I'm wrong, but if you choose to perform screenings limiting the participants to Juvenile diabetics, you would still need to identify, pre screening, the pathology (ies) in question and what environmental factors you wish to include. You would also need to factor in the age. You might be able to come up with a predictor for your pathology in question that could be proven or dis-proven over time.

    Steve
     
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