The linguistic confusion is easily exposed through the recent Regeneron study in Pennsylvania.

prevalence of ADH, Familial hypercholesterolemia, LDLR, APOB and PCSK9, FH patients

Note that FH-as-LDLR is 1:518 … still roughly the 1:500 estimated by the Nobel Prize winners. Nonetheless, this report became a jumping point for the lead author to claim on Twitter:

“FH is ~twice as common as it was thought to be.” (See illustration above.)

And here is a co-author in a press release, with a nearly identical phrase.

“The study shows us that FH is about twice as common as it was once thought to be …” [‘Geisinger and Regeneron study finds life-threatening genetic disorder is substantially underdiagnosed,’ Dec. 22, 2016]

But FH “was thought to be” FH-as-LDLR, which was estimated to be around 1:500 to begin with, and in this study FH-as-LDLR is still around 1:500.

As for the total prevalence, the Regeneron study and our passive mathematical exercise are not yet parallel. Earlier studies of FDB only counted the R3500Q mutation and concluded a prevalence between 1:1,000 and 1:1,250.