I'm 8th of 10 children. At least 3 of us are ASDers (the 6th or 7th [twins, and I don't know which one was born, first], me (the 8th), and the 10th - all girls. The woman who raised me (maternal aunt) had it, I'm sure (undiagnosed), and she was second-born. My biological mother had it, I'm sure, and she was 4th-born. Also, I'm sure my maternal grandfather had it (again, undiagnosed); but, I don't know what number he was (I don't THINK he was first-born, but I couldn't swear to it). I have a nephew who was second-born (well, really, THIRD born----first child died), and I'm sure he has it. I have another nephew who was first-born, who has it (undiagnosed). I have another nephew that was first-born who has it (undiagnosed). I don't really know my great-nieces and nephews, but since it has run so rampantly in my family, I'm sure there's a few in that generation, too.
So, let's see..... I think that's 5 generations with, possibly, only 2 first-borns.
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White female; age 59; diagnosed Aspie.
I use caps for emphasis----I'm NOT angry or shouting. I use caps like others use italics, underline, or bold.
"What we know is a drop; what we don't know, is an ocean." (Sir Isaac Newton)