Sunday, April 6, 2008

Population Genetics: A North Florida Hurler Club?

I have been rolling this around for a little while, and I'm still on the fence about it. I think it's kind of interesting that, of all the readers who have posted comments to this blog, and who are Hurler parents (that's what, seven or eight families?) four including Gracie's parents are along the I-10 corridor in North Florida.

So, is this a population blip or an information technology blip?

There is a temptation to jump to the conclusion that there might be a population of MPS-1 carriers in this area, but of course, right or wrong, this is pretty much statistical hooey. Here's why:
  • Four is not a statistically significant sample, even with the tiny population of Hurler kids that would be available for study. The number realistically exists on the level of coincidence.
  • Americans travel a lot. Gracie's dad is not from North Florida. Since Hurler is autosomal recessive, both parents have to be carriers for the gene to affect their child. Even though having one parent with an increased likelihood of carrier status (as would be the case with Sarah, if there were a concentration of carriers in N. Florida) does increase the total statistical likelihood for the couple, Jim's being a transplant dilutes the already pretty watery argument.
  • As it turns out, four Hurler kids living in North Florida isn't really that huge a number. 1:115,000 is a small chance, but given the large number of births that occur each year, it's big, but not enormous. In 2004, for example, 218,053 babies were born in Florida, of whom it is statistically probable that two were Hurler kids. Given improvements in treatment since that time, and much longer lifespans for children with Hurler Syndrome, it is not really that unreasonable to find four living children with Hurler Syndrome in Florida today. It's interesting to me that they seem concentrated in the I-10 corridor, though. It's a big state.

There have been reports of population concentrations in Hurler syndrome, as with many inherited disorders. One I read about was an elevation in a region of Northern Ireland. Isolated populations do tend to magnify genetic disorders, or just genetic differences, by intermarriage. The Ashkenazi Jewish population is a good example of this. Among other inherited disorders, this population, according to my reading, has a higher incidence of Hurler syndrome than the general population. Multigeneration North Florida families don't have the same degree of gene pool isolation, as they're all pretty mobile, but people who stay close to home in any population will naturally have a tendency to intermarry more frequently, right?

I do find it interesting that this population is so prominent on our blog. Does it mean that we're corresponding more with our geographic neighbors in this crisis than with people who live farther away? Surely the same internet is available to everyone, and people all over would find each other through the same channels that led us all here...

Anyone got any ideas about this?


Mr. Noodles Panini said...

I think it's interesting, if nothing else. And I think we could still start a club. :)

I'm not sure what proportion of those 218,000 births were in FL in 2004. But if we assume that the average life span for Hurler Kids is 10 (a safe bet given treatment advances), that would account for ~20 kids living with Hurler at a time. Unless 20% of all kids are born in FL (and 15% in Northern FL), the incidence of Hurler in N FL is relatively high. Also, those in FL that we know of are all MPS-1H, not MPS-1S. Does that make the incidence even more interesting? Not knowing enough about the genetics, I can't answer that question.

Anyway, I think it was an astute observation, sis. I grant you an honorary population genetics certificate. xoxox

mykidsmomx4 said...

I completely understand what you are talking about... there are so many variables and so much wondering... i love statistics. I really think they can be 'fun' ... but I think your blog really goes back to the one thing that so many parents go through... Where did I get this awful mutation? How could it be that I met the 1 in 25000 who have the same mutation and we made a child who had only a 1 in 4 chance of getting that mutation from both of us. Surely I could not just be this 'lucky' ... there MUST be a higher incidence in my area.

Both Lauren's dad and I are from this area. Born and raised 15 miles apart...families that have been here for many many decades. This would lead me to believe that there are other bloodlines here that are carriers. Yet Lauren's PT has heard of 4 MPS1 kids in 30 years. The only thing I can think of on my side is that nobody new My paternal grandfather except by name... could he have left even more of a legacy than he knew? Who knows...

As for the question of how so many Hurler's families have found you... we have a network. We have the MPS Forum. We have our own blogs... word gets around and people want to know that they are not the only ones. Even using Google, if someone found you that way, what key words would a normal person who had never heard of Hurler's before have to enter in? The likelihood is so small... besides the fact that there are surely more people who have found you, but not written because, as they have no connection to MPS, they read and move on.

mykidsmomx4 said...

Whoa.. I didn't mean to put an end to the discussion.

As for the 'club' part,I'd have to say that it would be a great support network for you guys!

By the way (not that you won't hav emore important things to remember) we will be in Minnesota from June 8th through the 16th.

See ya' there!

Testdriver said...

Ok, it's a club then! And I don't mean the Fred Flintstone kind, although I guess it's that, too, kind of...

The 218,045 number was for resident births in Florida during 2004, I got the number from Florida Vital Statistics. So, assuming a 10 year lifespan and a stable birth rate (it's actually going up), doesn't that suggest 20 in Florida at a time? I don't know, my math is rusty.

Anyway, since the people who visit us would probably skew young (as in more recently diagnosed) and are all 1H, we still might have a little blip. Even if we aren't statistically significant, we could still have a secret handshake and a couple of light hazing rituals...

Momx4, you're exactly the profile that supports this hypothesis, and I'd love to hear backgrounds on other N. FL Hurler families. I hope we'll see you in Minnesota, and I promise we won't make you drink beer out of an aquarium hose to get into our very exclusive club! ;)

Hys, Jim and G-love, We're sending you lots of love as you pack up for college!!! xo, Aunt Hyster