Genetic disease question

Jason Soon has his own blog here, but he also posts on Gene Expression. There he offers this in critique of an article by Bill McKibben.

The McKibben post eventually finds its way to discussing efforts of Ashkenazi Jews to eliminate Tay-Sachs disease. Tay-Sachs is a fatal hereditary disease caused when a child inherits the relevant genes from both parents. Genetic screening is being used to combat it.

OK, I can relate to this. To my knowledge I'm "clean". But a cousin of mine died slowly from MLD, another genetic condition that requires the relevant deadly genes from both parents. She was the younger of two girls, and her parents never had any more kids after her.

Then there's sickle-cell anemia, which is associated with Africa but can be found in other nationalities. If a child gets the gene from both parents it will suffer sickle-cell anemia. But having just one of the genes confers some protection against malaria.

So something is lost if the sickle-cell gene is eliminated. And I wonder if the same is true of Tay-Sachs or even MLD, such that carrying the gene is beneficial as long as you don't get it from both parents.

I'd have to pay to see the rest of the Times article, and I can't see giving those creeps a nickel as long as the current regime is in place. So I'm not sure exactly how far Ashkenazi Jews are going toward eliminating the gene. Selective abortion? Sterilization?

But I would be interested in knowing if the Tay-Sachs, MLD or other such potentially deadly genes offered any benefits to their carriers.