Yes, I was inaxact, sorry for that. Note that the term "mother" tongue is problematic in this context anyway, as there are many examples of caregivers and school systems not being fluent in sign language. I know a 70-something woman which turned out to have a deaf brother. Observing her while he was around, she didn't sign to him, she simply expected him to read from her lips. Which is very telling. Sign language is considered "their language" from her point of view, and she never aspired to actually learn it. After 50+ years of having a deaf brother... Just a recent anecdote, but still the norm. Deaf people have also been prevented from signing in certain schools. Similar things happened in the early days of Braille. Luis Braille never lived to see his system being used officially. He taught it in secret, as the power that be actually prevented it from being used for many decades. If you look long enough, there is a lot of patrnosation and ignorance in the way disabled people are treated by society, past and present.