I'm working on a sci fi story which heavily integrates themes of varying alien configurations and how they shape society, culture and language. As part of this theme, I want to have some of the human characters using a variety of different methods of communication, rather than falling into the "all humans communicate through spoken language and aliens have variations" trap. I decided to have a main human character who primarily uses a signed language, and have decided to 'make' her Deaf as a part of this. (Capitalized intentionally, see below.)
One thing I really want for this character is for her to come from a cultural background of heavy signed language usage. It's important to the themes and the character to have her come from a Deaf cultural background, and I'm looking for things which would cause and maintain a population with high stable rates of Deafness/hearing impairment as a result, which would still apply outside of her place of origin, as that is where much of the story is set. I've also decided for other reasons that I want her to come from a space colony near the setting location rather than from Earth itself.
The idea I have come up with is that this settlement is one of the earliest human settlements outside of the solar system, coming from an intergenerational starship with a minimal staff and a wide variety of frozen/preserved embryos meant to establish a human population upon arrival. The idea I had is that for whatever reason, those embryos happened to have a high frequency of Deafness, and as the years passed resulted in an established human settlement which mostly uses a signed language.
I do not need an explanation/justification as to why they wouldn't all use technology to become hearing. I have that covered. My question instead is: what sorts of causes might result in a population with widespread generational Deafness such as this? I had originally conceived of this as purely biological reasons and been looking for something which would specifically affect Deafness rates in the population, but some other suggested explanations have suggested environmental factors which could cause Deafness to be specifically created or selected for. These answers are also appropriate. I am not sure how to update the tags for this to reflect this.
The best answer will have a plausible genesis (such as a specific genetic syndrome and/or something which could cause stored embryos to be susceptible to it, or a reason for the starship to be originally crewed by Deaf folks) and a reason why it would be stable many generations down the line. Scenarios should be consistent with a culturally Deaf background and a signing background, rather than suggesting alternate means of communication technology.
EDIT: Okay. I was cool with the edit which removed some other plot details for clarity, but ever since it was made I've been getting "what if instead of Deafness you did [x]" answers, and that is not what I'm looking for. I specifically am looking for a Deaf culture here.