Four babies hemorrhage after parents refuse vitamin K shot, a practice on the rise

[jeff47]

135. Your excerpt doesn't conflict with the shot not affecting Factor 5.

The excerpt theorizes that Factor 5 was "ramped up" to deal with vitamin K deficiency. That doesn't mean having the shot would cause clotting - the two compounds work in different steps in clotting.

Essentially, they theorize that A lead to B. That doesn't mean B leads to A.

Additionally, these authors are just theorizing about why the Factor 5 Leiden evolved. There's no real causality here, there's an educated guess about causality. The fact that the Leiden allele is relatively rare is a problem for their theory. It either has to be relatively new, so that it has not had time to come to dominance, or it is not terribly beneficial. If it was as beneficial as their theory states, it would be far more common - for example, the sickle-cell genes are far more common than Factor 5 Leiden, and that has a very negative double-recessive condition.