Comments on: Pygmies are short because nature made them so http://blogs.discovermagazine.com/gnxp/2011/05/the-pygmies-are-short-because-nature-made-them-so/ Fri, 24 May 2013 15:27:00 +0000 hourly 1 http://wordpress.org/?v=3.4.2 By: omar http://blogs.discovermagazine.com/gnxp/2011/05/the-pygmies-are-short-because-nature-made-them-so/#comment-32990 omar Wed, 11 May 2011 19:46:50 +0000 http://blogs.discovermagazine.com/gnxp/?p=11610#comment-32990 Razib, you said "I believe that IGF can be found in meat and milk, so there are plausible dietary reasons that one could imagine this difference. " IGF-1 is found in meat and milk, but only in very small quantities and since it is itself a peptide, it is rapidly degraded in the GI tract, meaning you absorb very little of what you eat (which is why the only therapeutic form of IGF-1 is given via injection). There seem to be very few genetic defects in the IGF-1 gene itself that cause short stature. But keep in mind that the system works like this: Growth hormone circulated in the blood bound to GH binding protein, then binds to the GH receptor (interestingly, the circulating binding protein is nothing more than the extracellular part of the GH receptor). Once it binds to the receptor, it triggers a signalling cascade (the JAK-STAT pathway) that eventually increases IGF-1 production. A known, severe form of genetic dwarfism (Laron Syndrome) is usually caused by mutations in the GH receptor. But there are known (rare) defects in the JAK-STAT pathway that also cause short stature. Polymorphisms that decrease IGF-1 may occur in the IGF-1 gene itself but in this case, may be in the GH receptor (which would also decrease GH binding protein) or in the multiple genes involved in the JAK-STAT pathway. Dietary deficiency of IGF-1 would not explain this .But of course, lack of protein in the diet is a potent cause of short stature, only its not via differences in IGF-1 intake. Interestingly, Laron dwarfs are almost free of cancer and heart disease. http://www.nytimes.com/2011/02/17/science/17longevity.html Razib, you said

“I believe that IGF can be found in meat and milk, so there are plausible dietary reasons that one could imagine this difference. ”

IGF-1 is found in meat and milk, but only in very small quantities and since it is itself a peptide, it is rapidly degraded in the GI tract, meaning you absorb very little of what you eat (which is why the only therapeutic form of IGF-1 is given via injection).
There seem to be very few genetic defects in the IGF-1 gene itself that cause short stature. But keep in mind that the system works like this: Growth hormone circulated in the blood bound to GH binding protein, then binds to the GH receptor (interestingly, the circulating binding protein is nothing more than the extracellular part of the GH receptor). Once it binds to the receptor, it triggers a signalling cascade (the JAK-STAT pathway) that eventually increases IGF-1 production. A known, severe form of genetic dwarfism (Laron Syndrome) is usually caused by mutations in the GH receptor. But there are known (rare) defects in the JAK-STAT pathway that also cause short stature. Polymorphisms that decrease IGF-1 may occur in the IGF-1 gene itself but in this case, may be in the GH receptor (which would also decrease GH binding protein) or in the multiple genes involved in the JAK-STAT pathway. Dietary deficiency of IGF-1 would not explain this .But of course, lack of protein in the diet is a potent cause of short stature, only its not via differences in IGF-1 intake.
Interestingly, Laron dwarfs are almost free of cancer and heart disease. http://www.nytimes.com/2011/02/17/science/17longevity.html

]]> By: John Emerson http://blogs.discovermagazine.com/gnxp/2011/05/the-pygmies-are-short-because-nature-made-them-so/#comment-32989 John Emerson Tue, 10 May 2011 12:11:59 +0000 http://blogs.discovermagazine.com/gnxp/?p=11610#comment-32989 How tall are pygmies? The internets tell me that peoples are classified as pygmies if the average adult male is 5'1" or less. That actually overlaps the average height of historical poorly nourished populations elsewhere such as Japanese before 1850, or the French around 1800. I had thought that there was a separation, and that pygmies were seldom taller than 4'6" and that normal adults could be 4' even. Answer quickly because this is important to me. Adult males in my family average about 5'3 or 5'4. How tall are pygmies? The internets tell me that peoples are classified as pygmies if the average adult male is 5’1″ or less. That actually overlaps the average height of historical poorly nourished populations elsewhere such as Japanese before 1850, or the French around 1800. I had thought that there was a separation, and that pygmies were seldom taller than 4’6″ and that normal adults could be 4′ even.

Answer quickly because this is important to me. Adult males in my family average about 5’3 or 5’4.

]]> By: gcochran http://blogs.discovermagazine.com/gnxp/2011/05/the-pygmies-are-short-because-nature-made-them-so/#comment-32988 gcochran Tue, 10 May 2011 08:10:13 +0000 http://blogs.discovermagazine.com/gnxp/?p=11610#comment-32988 This is easy to do, but somehow I think we might have to wait a while before we see results on psychological quantitative traits. This is easy to do, but somehow I think we might have to wait a while before we see results on psychological quantitative traits.

]]>