New Study Challenges Long-Held Assumptions about NF1 Inheritance

New Study Challenges Long-Held Assumptions about NF1 Inheritance

November 5, 2026 Featured, Featured EU, NF1 , Science & Research

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Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic condition. This means that a person with NF1 has traditionally been understood to have a 50% chance of passing the altered NF1 gene to each child. This follows the principles of Mendelian inheritance, first described by Gregor Mendel hundreds of years ago, in which each child has an equal chance of inheriting either copy of a parent's gene.

However, a newly published study suggests that inheritance of NF1 may not always follow this expected pattern, adding another layer of complexity to NF1.

By examining 322 complete, well-characterized families (with a total of 701 children), researchers found that 61% of the children had inherited NF1, significantly more than the 50% expected under Mendelian inheritance.

The study, "Transmission Ratio Distortion of NF1 Mutant Alleles in Familial Neurofibromatosis Type 1," was published in Genetics in Medicine .

What Did the Researchers Find?

The researchers combined data from four well-characterized groups of families affected by NF1. They applied strict inclusion criteria to reduce potential sources of bias, such as excluding possible cases of mosaic NF1, and only including families where one parent had NF1 and the other did not.

Among the 701 children included in the analysis, 428 had NF1, representing 61% of the total. The researchers also examined whether inheritance differed depending on which parent had NF1:

• Among children whose mother had NF1, 62.8% had the condition.
• Among children whose father had NF1, 58.5% had the condition.

Although the proportion was slightly higher when NF1 was inherited from the mother, the difference between maternal and paternal transmission was not statistically significant. The researchers also investigated whether factors such as family size could explain the unexpected result. The excess of affected children persisted across the additional analyses.

This pattern is consistent with a phenomenon known as"transmission ratio distortion" which occurs when one version of a gene is passed on more frequently than the 50% expected under Mendelian inheritance. Transmission ratio distortion has also been described in a small number of other inherited conditions, suggesting that departures from Mendelian inheritance may be more common than previously recognized.

Does This Mean the Chance of Inheriting NF1 Is Now 61%?

Not necessarily.

Although this study included enough families to detect a statistically significant departure from the expected 50% inheritance pattern, the observed 61% represents an average across the study population, not an individual risk estimate. It does not mean that every person with NF1 has a 61% chance of passing their NF1-affected gene copy to a child.

We do not yet know how increased transmission risk could vary between families. It is possible that some families follow the expected 50% inheritance pattern, while others have a substantially higher risk. At the moment, it is not known whether having more than half of the children affected in a family is just by chance or if there is an underlying biological reason. Answering these questions is an important next step.

For now, the established guidance should remain unchanged: a person with NF1 is counseled that each pregnancy carries a 50% chance of inheriting the condition, assuming that the other parent does not have NF1.

Co-authors Anne Goriely and Peggy Wallace explain,

"The 61% figure is an average across our entire set of 322 families. Some families may have the expected 50% risk, but others may have a higher risk. Understanding the biological basis of this finding could eventually lead to more accurate, personalized genetic counseling to individual families."

How can we explain this unexpected finding?

If confirmed in studies of additional groups of families, the findings raise an intriguing biological question: why might the altered NF1 gene be inherited more frequently than expected?

One possible explanation proposed by the researchers involves a process called germline selection. Germline cells are the cells that give rise to eggs or sperm. The researchers propose that cells carrying changes in the NF1 gene might gain a growth advantage during early germline development, making the altered gene more likely to be passed on to the next generation.

This hypothesis draws on what is already know about NF1 biology. The NF1 gene produces neurofibromin, a protein that helps regulate cell growth through the RAS/MAPK signaling pathway. Reduced neurofibromin function can provide a growth advantage, contributing to the development of NF1-associated tumors. Whether a similar advantage occurs in developing reproductive cells remains unknown.

Importantly, germline selection is currently a hypothesis, not an established mechanism for the findings. The study analyzed inheritance within families but did not directly investigate reproductive cells or biological processes that could be responsible for the observed excess of affected children. Further research will be needed to determine whether germline selection, another biological mechanism, or factors related to the study population could explain the results.

Why This Research Matters

Although the findings do not immediately change clinical guidance, they raise important questions about the inheritance of NF1, a condition long considered to follow a straightforward Mendelian pattern.

Understanding whether an altered NF1 gene is preferentially transmitted could eventually have implications for:

• Genetic and reproductive counseling
• Prenatal and preimplantation genetic testing
• Our understanding of germline development
• Scientists' broader understanding of how NF1-related genetic changes influence cell behavior.

The research may also have implications beyond NF1. Transmission ratio distortion has been reported in a small number of other inherited conditions, and studying it in NF1 could help scientists understand how disease-associated genetic variants may influence their own inheritance.

What Families Should Know

For individuals and families with NF1 the findings may raise questions about the likelihood of passing the condition to future children.

The key message is that this study does not currently change the established 50% inheritance risk used in genetic counseling. However, the findings suggest that NF1 inheritance may be more complex than previously understood and that the conventional 50% estimate may not accurately reflect the risk in every family. Further research is needed before more personalized risk estimates can be offered.

People with NF1 who are considering having children should continue to seek advice from a genetic counselor or another qualified genetics professional, who can explain the current evidence, discuss reproductive options, and help families make informed decisions based on their circumstances and preferences.

This study opens an intriguing new avenue of NF1 research. By challenging a long-standing assumption about how NF1 is inherited, it highlights the need to better understand the biological processes that shape genetic transmission and whether transmission risk varies between families. Confirming these research findings will be essential before they can inform changes to clinical recommendations.

Read the publication in Genetics in Medicine.