I have no idea about any of the family's medical history. Johnnie's parents were Mexican immigrants who hadn't been in the U.S. that long when he and Joe were born (I think they came here in 1944, the twins were born in 1951), so all of the Herrera kids were probably fluent in Spanish, or at least had a working knowledge of the language.
The thing that no one seems to be able to give me answers to is whether or not the people at the party actually said they saw Johnnie leave. All anyone seems to be able to say is that he was at the party. I was hoping to get that question answered when I e-mailed the Oxnard PD a few months back, but you saw the somewhat passive-aggressive response I got (it's posted a few pages back), so it doesn't really make me want to go out of my way to ask them anything again.
The first detective I talked to a few years ago, Lynette Fenton, who actually is in charge of Johnnie's case, told me that there were "indications of money and marital problems" and that "some people [she never specified who] felt that Johnnie only married her [Annette] because she got pregnant". Given the values of the era, I have little doubt that the unplanned pregnancy was what prompted them to marry. However, the marital and money problems thing is at direct odds with Johnnie's family's insistence that everything at the time of the disappearance was fine. Something isn't right there.
I suppose both versions could technically be true. For example, Johnnie may have been able to keep his emotions in check around his family and put on a convincing show of being content, only to vent to his friends about how upset he was when his family wasn't around. In other words, the family only saw Johnnie as happy because that's how he purposely portrayed himself in their presence, but the friends saw a completely different Johnnie. So each side is going by what they themselves witnessed.
Could something have happened that night, either at the party or at home, that caused Johnnie to simply snap and cut off all ties?