Living with Phenylketonuria is a challenge in and of itself, as anybody that deals with it can likely tell you. It takes a strong commitment to building habits and sticking with a routine to manage the symptoms it brings; it’s no surprise that soon-to-be parents would be concerned about the chances of potentially passing it on to their children. With 1 in 10,000 to 15,000 newborns diagnosed with PKU every year, what are the odds of your child having it too if you do?
If it’s been a little while since your last biology class, don’t worry, we’ve got you covered.
Each cell in the body contains a total of 46 chromosomes (essentially long strings of genes) that are arranged into a total of 23 pairs, one from the mother, and one from the father. These genes are the equivalent of an instruction sheet; they send the information needed to grow, develop, and stay healthy to the various parts of the body.
The 23 pairs of chromosomes are each labeled with a number, and these numbered pairs are called the autosomal chromosomes. Since chromosomes show up in pairs, it’s important to remember that there are two copies of each of the genes as a result. If a change in DNA happens in only one pair of genes that causes a health condition, it’s then referred to as a dominant mutation. On the opposite hand, if it only occurs in the event of both copies of the gene being changed, it’s then called a recessive mutation.
Where does PKU fall? That would be under the autosomal recessive category.
Autosomal recessive what now?
Phenylketonuria is classified as an autosomal recessive disorder, which means that it’s something inherited when a mutated gene is passed on from each parent. Autosomal because it shows in those pairs of genes, recessive because it requires both copies to be changed to occur. In many cases the parents may be carrying a mutated copy of this gene, but may not show signs or symptoms of the condition whatsoever; this is because in most cases the gene is typically recessive to its working counterpart gene.
So what are my odds?
This is where things tend to get a bit trickier. As mentioned above, there are many instances where people will carry the gene that could cause PKU, but it’s balanced out by a working gene; this means that a completely healthy person with no signs of PKU whatsoever still could potentially pass it down. Without knowing for sure whether you carry that gene, there’s a level of guesswork involved.
*Disclaimer: We are not biologists, nor are we doctors, we’ve just spent a lot of time researching this as an area we care deeply about.*
With that being said, here are a few possible ways it could play out:
1 parent has PKU, 1 does not (nor do they carry the gene)
There is a 100% chance that the child will be born with the faulty gene, but it will be matched with a working gene; they could potentially pass it on to their children if they were to have a child with someone who has PKU, but they should be fine.
1 parent has PKU, 1 does not (but carries the gene)
This scenario represents a 50% chance of the child being born with one working gene and one non (above scenario, unaffected) and a 50% chance of being born with both affected genes and having PKU.
Both parents have PKU
Statistically speaking, if both parents are passing on the same mutated recessive gene (as they wouldn’t have a working gene to pass on), there’s a near 100% chance that the child will be born with PKU.
Neither parent has PKU (but both carry the gene)
This situation is a classic example of odds. There’s a 25% chance in this case that the child will inherit a working gene from each parent, which makes them entirely a non-carrier. There’s a 50% chance that the child will have both a working gene and a nonworking gene, which makes them a carrier, but one that’s not likely to ever experience the symptoms of PKU. The remaining 25% makes up the chances of the child inheriting a nonworking gene from each parent, and thus being diagnosed.
As you can see, a major factor here is whether or not one of the parents carries the recessive gene as well, which they may not even know themselves. These kinds of things can be tested for with a doctor if it’s something you’re genuinely concerned about, but you’ll have definitive answers when the little bundle of joy actually arrives. A diagnosis isn’t the end of the world though; sure it makes things tricky, but a parent that’s been there and done that can help a child to overcome anything.