I think you have a great attitude Dr. John, and that might be because you and your son's have the diagnosis of Asperger's, which is higher-functioning. You did great, and I'm sure you are helping your teenage sons to do the same.
Those of us who have lower-functioning children know that without the diagnosis, our children are not provided with the appropriate and necessary supports that they need in school, and life.
My son would probably be in a mental hospital, or a group home somewhere, without the few programs, supports and services out there to help him. I kept him in school until the age of 21 1/2, and then, thankfully, his name came up for the Adult Autism Waiver. He lives on SSI, which he could never have qualified for without the diagnosis, in subsidized housing.
My point is, without the diagnosis, many children will not be able to receive the support services they are entitled to in school, in their IEP, and as part of their transition into independence and adulthood.
I hate labels too, but the label did not stand as an obstacle to anything positive for my son, it served as a bridge to the things he needed in order to be the best he could possibly be.

The real answer has to be this:
Yes--No--Maybe
I know families that have 4 out of 6 on the spectrum, from mild to severe. I also know some who have the oldest 2 on the spectrum, both in the middle of the severity scale, but not at all in the last 3.
I believe that there are a lot of factors at play in Autism. Some of them we have no control over. But some we do, like early intervention and how we deal with it in our home and family.
I hope that this is not the deciding factor for you in having more children or not. While it can be very hard to deal with, it isn't the end of the world.
It will be what you make of it. That may sound harsh, because some kids really have sever difficulties. But I firmly believe that if you love your child and there is a unifying love between you and your spouse, you will be able to handle the things in your life. If you look at things negatively-it will be negative! If you look at the possibilities-you will find help and answers.
I have a daughter in the spectrum. Now she is 19 and pretty high-functioning. But that was not always the case! We have gone through times of severe difficulties, horrible behavior that we felt we couldn't tell anyone about. We have been beaten on, bitten, had to clean up #2 from all kinds of places, had to put many locks on our front door and she still would get out, we had to get her off the roof of our neighbors house, had people call and tell us she was riding someone else's bike and she was naked. We honestly thought that she would end up not being able to live with us.
But we loved her. We sought treatment and paid attention to how it was or wasn't working! We knew her better than anyone else so we made the choices and we made the sacrifices. No, it wasn't something I wanted to go through, even now it can be very hard. But we still love her. We still help her, we see how all of our sacrifices and work have paid off. It is totally different than the satisfaction I have in my 2 older children. It has more meaning and more tears are shed much easier over knowing how hard she had to work along with us.
Autism isn't the end of our dreams for our child. It is the opportunity to really learn about our child and then help them with the strengths they have.
It is a different road than you planned, that's all!

I am the father of two sons, ages 19 and 15. Both have an Asperger's (now HFA) diagnosis. I have been informed that I am an adult with residual Asperger's.

In my youth, it was not an official diagnosis, and I am glad of that, as I find educators overwhelmingly use the label to pigeon-hole kids and push them off onto life-limiting non-diploma tracks at school. Absent that label, the teachers who educated me just adapted there approaches to me to overcome my "oddness".

As a result, I graduated with a high school diploma, earned a bachelor's degree from university, earned a podiatric medical degree, and have built a successful practice specializing in lower-extremity wound care/limb salvage and preservation.

The point?

1. It is not uncommon for more than one child in a family to be on the spectrum. I don't know the exact statistic, and given the state of autistic spectrum disorder research and knowledge, I would not trust that statistic.

2. Don't let ANYBODY turn the diagnosis into a label and pigeon-hole your ASD child. Don't let anyone assume your child can or cannot do ANTHING because of the diagnosis, and thus impose limits upon him or her instead of exploring every option, leaving no stone unturned, and facilitating your child to achieve to his or her fullest potential.

3. Don't allow yourself to despair because of your child's diagnosis--don't YOU fall into the trap of turning the diagnosis into a label. Remember that our children, with the right approach, can achieve extraordinary things.

Dr. John L. Trench III
Advanced Wound and Limb Care Center
Terre Haute, Indiana

I have 5 children Julian being number 4 and only he is affected. I am an only child myself and have not ever heard that any of my cousins or their kids have autism.

Odds higher, yes. However, it isn't about playing odds, but celebrating individuals. I have one child on spectrum, one that isn't. I am on spectrum myself. I have family that is, and family that isn't. We are all wonderful individuals with our own strengths, difficulties, and personalities.