Blog

by Shannon Weiloch, Fairfax Cryobank Genetic Counselor

One of the most common questions we hear is: “Why wasn’t that tested for?” 

It’s such an important question, and one that makes complete sense to ask. From the outside, it may feel like genetic testing should be able to cover every possible condition. 

The truth is, there are a few roadblocks that make testing for certain conditions challenging—or sometimes even impossible right now. Below, we’ve outlined some of the most common limitations of genetic testing to help bring clarity and reassurance. 

Launched in October 1990 and completed in April 2003, the Human Genome Project (HGP) generated the first sequence of the human genome. Think of it like the original AAA road maps your parents might have used for family road trips—the ones that no one could ever fold back up correctly. The HGP gave us a broad outline of the route, but more than 20 years later, we’re still learning the details of every twist and turn along the way. 

Here’s why: 

• Humans have about 20,000 genes. 

• Only 6,000–8,000 genes have well-characterized functions described in the scientific literature. 

• Just 4,000–5,000 genes are known to be related to Mendelian (single-gene) diseases, according to databases like OMIM (Online Mendelian Inheritance in Man). 

That means thousands of other genes are either: 

• Poorly understood, 

• Still being actively studied, 

• Tied to complex traits like height, diabetes risk, or intelligence, or 

• Functionally redundant or only relevant in specific tissues or conditions. 

In short: we can only test for what we know — and there’s still a lot we don’t fully understand. 

Even when we do know a gene’s function, different changes (variants) within the same gene can affect health in very different ways. And beyond genes themselves, we also have large stretches of DNA that don’t code for genes but still regulate how genes function. 

Finally, many common conditions — such as diabetes, heart disease, autism, and mental health challenges — aren’t tied to a single gene at all. Instead, they arise from hundreds or even thousands of genetic variants interacting with environmental factors.

So, while our understanding of genetics has come a long way, it’s important to remember how much we’re still uncovering. 

What this means for Fairfax Cryobank donors 
At Fairfax Cryobank, every sperm donor undergoes one of the most comprehensive genetic screening processes in the industry. Our testing panel screens for 500+ genetic conditions to provide families with the most accurate, reliable, and meaningful information available today. 

That said, no testing panel can cover every possible condition, and the limitations described above apply across the entire field of genetics. This is why we are transparent about what is tested, continually review and update our panels, and encourage clients to consider carrier screening for themselves as well. 

Our priority is to give you confidence and peace of mind as you navigate the various details of using a sperm donor to build your family. Are you ready to select your donor? I am available to help answer your genetics-specific questions and work with you to find a donor that is a good match for you.

You can contact me at 703-509-1085 or [email protected].

Shannon Weiloch
Fairfax Cryobank Genetic Counselor