Genetics and Family Risk in PFBC

Understanding why Primary Familial Brain Calcification (PFBC) runs in some families while affecting individuals differently starts with the genes. Genetic testing can often identify a specific “typo” in your DNA that caused the condition, but it is important to remember that having a genetic variant does not always mean you will feel sick ^[1][2].

How PFBC is Inherited

PFBC can be passed down in two different ways, depending on which gene is involved. This pattern determines the risk for your children, siblings, and other relatives ^[3][4].

• Autosomal Dominant (AD): This is the most common form. It means you only need to inherit one copy of the “typo” gene (from either parent) to be at risk for the condition ^[3]. The genes associated with this pattern include SLC20A2, PDGFRB, PDGFB, and XPR1 ^[3][5]. In these families, each child of an affected person has a 50% chance of inheriting the gene variant, not a 50% chance of developing symptoms.
• Autosomal Recessive (AR): This form is less common and usually occurs when a person inherits two copies of the “typo” gene—one from each parent ^[3][6]. The parents are usually “carriers” who do not have the disease themselves. The genes for this pattern include MYORG, JAM2, and NAA60 ^[7][8]. In these families, if both biological parents are carriers, each child has a 25% chance of inheriting both copies. The risk is different when one parent is affected or the partner’s carrier status is unknown.

Imaging vs. Clinical Penetrance: The Great Variable

One of the most confusing parts of PFBC genetics is penetrance—the likelihood that a person with the gene will actually show signs of the disease ^[9].

• Imaging Penetrance: This refers to whether calcification shows up on a brain scan. For dominant genes like SLC20A2, imaging penetrance is reported in some studies as nearly 100%, meaning almost everyone with the gene will eventually have “spots” on their CT scan ^[9][1].
• Clinical Penetrance: This refers to whether a person actually develops symptoms, like movement or mood changes. Clinical penetrance is much lower, estimated in a pooled review at roughly 61% across the most common genes ^[9].

These are research estimates from specific cohorts, not predictions of your personal future. This means it is very common to have a family member who “tests positive” on a brain scan but feels completely healthy ^[10][11]. For example, about 54% of people with a PDGFRB variant in one cohort never develop clinical symptoms ^[1].

Genetic Counseling and Testing for Families

Deciding whether to test family members who have no symptoms (asymptomatic relatives) is a deeply personal choice. There is no universally established schedule for imaging or testing asymptomatic relatives. The 2025 international consensus guidelines emphasize that genetic counseling should be a core part of your care ^[4].

A genetic counselor can help your family navigate:

1. The “VUS” Challenge: Sometimes testing finds a Variant of Uncertain Significance (VUS)—a genetic change that we don’t yet understand. A VUS should not be used to make medical decisions or to diagnose relatives ^[12][11].
2. Negative Results: A negative panel does not exclude PFBC. A substantial proportion of clinically suggestive cases remain genetically unresolved, as not all causative genes are known ^[4].
3. Reproductive Planning: For people considering having children, understanding whether their PFBC is dominant or recessive can help clarify the risks for future generations ^[3][6].
4. The Impact of Knowing: Since there is currently no “cure” that stops calcification, some family members may prefer not to know their status, while others find the information empowering for their future health planning. Testing decisions should consider privacy, insurance, and psychosocial implications where relevant ^[13][4].

Current guidelines recommend using comprehensive next-generation sequencing (or even whole-genome sequencing) to get the clearest picture of your family’s genetic landscape, usually guided by your genetic counselor ^[4].