They are a totally different type of brindle Matt
American Brindle is Avy, X-Linked Brindle (Which is what Sarah has) is MoBr.
The males die because of a severe deficiency of copper, because this gene prevents them from synthesising it. There has been tests in labs, where they inject male babies at 16 days old with a copper infusion to prolong life, but, as Sarah says above, the males even at breeding age, don't seem to be fertile.
The MoBr gene is linked to the X cromosome, but because females have two X's... the non attached X compensates for the copper thing, and females are generally very healthy.
As much as it would be easier for this variety to have the occasional male live long enough to sire offspring, it would then create the potential problem of non-viable females too, if they were homozygous and inherited the MoBr gene on both of thier X's