Probably not.

> Mother-to-offspring prion transmission appears to be prion-strain specific as evidence in other animal species including humans, Syrian hamsters and sheep infected with the classical bovine spongiform encephalopathy (BSE) agent show that progeny from infected females at the moment of gestation do not develop prion disease in the long-term

—Detection of CWD prions in naturally infected white-tailed deer fetuses and gestational tissues by PMCA

As that article and several others show, some prion diseases such as chronic wasting disease of deer can spread from mother to fetus, but there’s no evidence of that ever having happened in humans.

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> prion-strain specific

What is a "prion strain"? Are there different misfolded forms of PRNP?

Yes, certainly. That's why there are multiple different prion diseases in humans, such as Creutzfeldt-Jakob Disease, Gerstmann-Straussler-Scheinker Syndrome,Fatal Familial Insomnia, and Kuru.

>Although PrPC is encoded by the host genome, prions themselves encipher many phenotypic TSE variants, known as prion strains. Prion strains are TSE isolates that, after inoculation into distinct hosts, cause disease with consistent characteristics, such as incubation period, distinct patterns of PrPSc distribution and spongiosis and relative severity of the spongiform changes in the brain. The existence of such strains poses a fascinating challenge to prion research.

--Insights into prion strains and neurotoxicity

Isn't FFI an example of what OP was wondering about? Or is it different because it's the gene responsible for causing it that's passed down, not the proteins themselves?

I’m only in undergrad, but I do all of my projects and papers on prions and I am under the impression the second thing you said is true, it’s just the genetic basis.

FFI is caused by a mutation in the PrP gene that predisposes it to misfolding causing disease. If this DNA mutation is not passed down to the fetus, then it won't get the disease even if the mother has FFI. The misfolded protein itself will not be passed from mother to fetus.

www.science.org/doi/abs/10.1126/science.1439789

I see, thank you!