Can You Get FSHD Without a Family History?

Yes, you can absolutely develop facioscapulohumeral dystrophy (FSHD) even if no one else in your family has it. In fact, between 10% and 30% of all people diagnosed with FSHD have no documented family history of the disease ^[1][2].

When someone is the first in their family to be diagnosed with a genetic condition like FSHD, it is usually the result of a spontaneous genetic change, which doctors call a de novo mutation.

How Spontaneous (De Novo) Mutations Happen

Our bodies are constantly building and copying DNA. Sometimes, during the formation of an egg or sperm cell, or very shortly after an egg is fertilized, a copying error occurs.

In the case of FSHD, this usually means a specific section of DNA on chromosome 4 (called the D4Z4 repeat array) becomes unexpectedly shortened, or “contracted” ^[3]. This contraction is the hallmark of FSHD type 1 (FSHD1) and leads to the inappropriate activation of a gene called DUX4, which causes muscle damage ^[4]. Less commonly, a spontaneous mutation can occur in a different gene, such as SMCHD1, which causes FSHD type 2 (FSHD2) ^[5].

If these acronyms feel overwhelming, don’t panic. You can look at your genetic test results or ask your doctor to clarify exactly which type you have, as this helps map out your specific condition. Notably, some research suggests that spontaneous (de novo) mutations—particularly in FSHD1—can sometimes lead to symptoms starting earlier or varying in severity compared to inherited cases ^[6][7].

If you have a de novo mutation, you did not inherit the disease from your parents in the traditional sense; the genetic change started with you.

The Role of Mosaicism in Parents

In some cases where there appears to be no family history, one of the parents may actually carry the genetic change, but only in a small percentage of their cells. This phenomenon is called mosaicism ^[8].

Because the mutation is only present in a fraction of their body cells, the parent usually does not have any muscle weakness or symptoms of FSHD. However, if the genetic change is also present in their reproductive cells (sperm or eggs), they can pass the fully developed mutation to their child ^[9].

If your parents are considering having more children, or if you have healthy siblings who are planning families, they may want to speak with a genetic counselor. Highly sensitive genetic testing can determine if either of your parents has low-level mosaicism, which can help assess the risk for your siblings ^[10][8].

Passing the Gene to Future Children

It can be confusing to realize that you are the first person in your family to have a genetic disease, but you can still pass it down to the next generation.

Once a spontaneous mutation happens early in your development, it becomes a permanent part of your genetic blueprint. For the most common form of the disease (FSHD1), the condition is autosomal dominant. This means it only takes one copy of the altered gene to cause the disease ^[4][11]. Because you have one affected chromosome and one unaffected chromosome, there is a 50% chance with each pregnancy that you will pass the FSHD1 gene to your child ^[12]. (FSHD2 inheritance is a bit more complex, often requiring two specific genetic factors to align).

If you are thinking about starting or expanding your family, meeting with a genetic counselor can be incredibly helpful. They can discuss reproductive options with you, including specialized prenatal testing or in vitro fertilization (IVF) techniques that screen embryos for the FSHD gene before pregnancy ^[13][14].