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?