My Father,  Two Brothers,  Both sons, and 3 nephews have Aphantasia.   I can confirm it is genetic.  

Have you ever read this theory about language evolution, it's a wonderful read and speaks to the potential impact slight variations in cognitive processes could have. I do tend to think these variations in imagery abilities are evolutionarily fit divergences, there are obvious collective advantages in diversity. And there is definitely scientific interest into this question of genetics, it's only a matter of time before we have some more conclusive answers. But as Shannon mentioned, the current data does suggest the possibility of a genetic component - aphantasics in that study were shown to be 10x as likely to have a 1st degree relative with aphantasia.

As recently as 2020, the only thing known about a genetic basis for aphantasia is that it runs in families more often than would be expected by chance (Zeman et al., 2020). So there probably are genetic markers, they're just totally unknown so far. Let's hope someone researches it soon!