I'll share a story. I have a frameshift mutation on a particular gene. It has been noted to be connected to speech delays, amongst other things. My son has the same mutation. However, he is globally delayed and has many issues. Normally, when you still have one good copy, whatever "abnormal" traits there are, it should be minimal as opposed to severe. However.... He had a very traumatic birth and was premature and not breathing and had lactic acidosis. My thoughts are that the traumatic events that happened to my son made whatever genetic predispositions he may have had, present themselves. This particular gene is crucial to neurodevelopment, and I think since his body was under extreme stress at birth, the one good copy wasn't enough to work properly. So, along those lines, could there a have been a genetic component triggered because of an accident during the prime age of speech development? Sure, I think it's plausible.