Hi Natalie,

To answer your question about WHAT an exon is, and whether it is harmful:

In essence, an exon is nothing more than an area on a gene...sorta like a neighborhood. Think of the 21-hydroxylase gene as a big city, made up of 10 distinct neighborhoods. An "exon" would be one of those 10 neighborhoods....kinda like saying you live in the "Beacon Hill" area of Boston.

Since there are so many pieces of DNA on a gene--much like there are many houses in a big city---knowing where a piece of DNA is located on a gene (e.g. exon 10) helps scientists know where to look for problems. Much like knowing which neighborhood you live in helps someone find your house in a big city.

So, an exon is not an inherently good or bad thing. It is just a term used to identify a particular place on a gene.

"Introns" are also places on a gene. But, introns are places where not much happens. So, if exons are neighborhoods where there are lots of houses and people, then introns are kinda like the undeveloped areas and vacant houses in-between.

Well, enough of the real estate analogies...(haha!)...and on to the issue of the "misdiagnosis."

Personally, I think it is a bit premature to say that there was a misdiagnosis, when TWO mutations have been found in your daughter’s DNA. As you said earlier, if these mutations each occured on different copies of her 21-hydroxylase genes, then she would have CAH, after all. So--to me--it seems possible that the "misdiagnosis" could (unfortunately) itself be a "misdiagnosis."

Like Martha, I am suprised that they are unable to tell if your daughter’s mutations occur on different gene copies (which would make your daughter have CAH) or the same gene copy (which would make your daughter a carrier.) If it were not possible to tell which gene copy is affected, then DNA testing would more or less be worthless for everyone, since one would NEVER be able to distinguish between an affected person or a carrier. I would ask the geneticist to clarify this.

As for your daughter’s original diagnosis of CAH: I would certainly hope that the md didn’t just "assume" that she had CAH, based on the fact that her sister had CAH. However, if she had significantly elevated adrenal hormone levels, then the diagnosis coud certainly be made, even without an ACTH stimulation test. So, to get to the bottom of whether or not she has CAH, it seems important to know what her hormone levels were at the time of diagnosis. Also, what they are now, that she is being weaned off medication. If they are significantly elevated without medication, then---unfortunately--she may have CAH, after all.