The differences between the types?

Todays thoughts revolve around the broad nature of the condition.

So, I have looked at the condition in types, of which there are two (see 25th Feb http://hspjourney.blogspot.com/2011/02/condition-in-types.html) and I mention the different HSP variants on 25th March (http://hspjourney.blogspot.com/2011/03/interpreting-genetic-test-results.html). I haven't looked into the different dominant/recessive/x-linked recessive variations either.

The different pages which describe the condition are fairly general about when people first get onset of the condition and are even more general about how severe the effects might be. For example, this page http://www.ncbi.nlm.nih.gov/books/NBK1509/ gives listing of various SPG variants (up to SPG33), and with each one there's a range of onset ages. I note that in July '10, SPG48 was identified http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1000408.

I presume that that variation in severity is due to the amount of degradation in the nerves in the spinal column, but, I dont know the link between the particular SPG genetic modifications and the degradation of the nervous system - a topic for another post, perhaps. I am not surprised that there is variation in the condition given the ~50 variants, each with a range of onset age. I cannot decide if I should be surprised if 50 different variations give rise to the same broad symptoms though.

(However, if I think of potential reasons for my computer behaving slower at times, perhaps I should not be suprised, given the further complexity of the human body....)