TL;DR
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A study of 3,524 people with frontotemporal dementia or motor neuron disease identified 793 related pairs, including many connections not previously recognized. The genetic family maps may help researchers investigate disease-linked genes and show that people diagnosed with apparently sporadic disease can share ancestry with other affected participants.
Researchers have used DNA from 3,524 people with frontotemporal dementia (FTD) or motor neuron disease (MND), also known as ALS, to uncover previously unrecognized family connections and construct 73 DNA-based family trees. The study, published in the journal Brain, suggests that genetic links can be missed by conventional family histories, potentially giving researchers more relatives to compare when searching for disease-associated genes.
The research team, involving scientists from the Macquarie University Brain Institute and Clinic, analyzed data from participants in Australia, New Zealand and the United Kingdom. Using a method called cryptic relatedness analysis, the researchers detected relationships ranging from siblings to third cousins. They identified 793 related pairs; more than 30% of the relationships had not previously been recognized.
The newly identified connections helped researchers assemble 73 family trees based on shared DNA among people whose disease had no known genetic explanation. Comparing affected relatives can help narrow the DNA regions they inherited from a common ancestor, the researchers said, creating a way to make more use of existing patient cohorts in searches for disease-linked variants.
The team also traced shared ancestry around known ALS and FTD genes, including SOD1 and C9orf72. The analysis identified networks of people carrying the same genetic change who may share a distant ancestor, even when their families appeared unrelated. Some of these connections crossed national borders, linking participants in Australia, New Zealand and the UK.
The results matter because researchers studying adult-onset conditions can have limited information about a person’s family history. A family may be small, records may be incomplete, or relatives carrying a disease-associated variant may never develop symptoms. In those circumstances, people who appear unrelated on paper can still share inherited DNA.
Identifying those relatives may give researchers more affected individuals to compare, which could help them prioritize parts of the genome for further study. The work does not identify a new cause of ALS or FTD by itself, nor does it establish that every detected family connection explains a participant’s illness. Instead, it offers a method for finding relationships that can support future gene discovery and research into why similar inherited backgrounds may be associated with different outcomes.
The findings also complicate the distinction between “familial” and “sporadic” disease. The study reports that, among participants clinically recorded as having sporadic disease, almost 16% of those with FTD and 5.5% of those with ALS were genetically related to another affected person in the cohort. Those figures describe this study group; they are not estimates of the share of all people with either condition who have an affected relative.
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How DNA Reconstructed Family Trees
In an inherited condition, a family history can help researchers identify relatives who might share a genetic change. But FTD and ALS often begin in adulthood, and a genetic variant associated with disease may not lead to symptoms in every person who carries it. The study’s lead author, Dr. Lyndal Henden, said these factors can make family connections difficult to recognize through reported histories alone.
Cryptic relatedness analysis looks for evidence in DNA that two people share ancestry, even when they are not known to be relatives. In this study, researchers applied the approach to a combined dataset of people with FTD and MND/ALS, then used the detected connections to construct family groupings and examine ancestry around established disease genes.
The study, titled “Identity-by-descent to resolve reduced penetrance and advance gene discovery in neurodegenerative disease,” was published in Brain in 2026. Its authors include lead author Henden and senior author Professor Kelly Williams. The reported analysis is a research tool for understanding shared genetic backgrounds; it is not a clinical test result for any individual reader.
“Where we might have had only one person to study, we can now compare affected relatives and prioritize the regions of DNA they inherited from the same ancestor.”
— Professor Kelly Williams, senior author
Limits of the Findings
The study identifies genetic relationships, not a diagnosis or a proven cause for each person’s disease. The source report does not specify how many new disease-causing variants, if any, were established through the family trees, or whether the analysis has yet led to changes in clinical care. It also does not give enough detail to assess how representative the cohort is of all people with ALS or FTD.
The reported percentages for participants labeled as having sporadic disease apply to those enrolled in this dataset. They should not be read as population-wide rates. The researchers also found that genetically related participants could have different diagnoses, but the available report does not establish why shared ancestry was associated with different clinical outcomes.
The immediate next step is further research into the DNA regions shared by affected relatives, including people whose disease does not yet have a known genetic explanation. Researchers can use the reconstructed families to prioritize candidate regions and test whether they contain variants linked to disease.
The published study does not set out a timetable for identifying additional genes or describe a planned clinical application. Any proposed disease link would need further investigation; the current findings support a way to organize and study genetic data, rather than a new screening recommendation. The key question for follow-up work is whether these family connections help researchers identify variants and clarify why inherited genetic backgrounds can lead to different diagnoses or symptom outcomes.
Key Questions
What did the researchers find?
They identified 793 related pairs among 3,524 people with FTD or MND/ALS, with more than 30% of the relationships not previously recognized. The analysis also produced 73 DNA-based family trees.
What does cryptic relatedness analysis mean?
It is a method for using DNA data to detect shared ancestry between people who may not know they are related or may not appear related in their family histories.
Does the study identify a new ALS or FTD gene?
The report describes family mapping intended to support gene discovery and analysis around known genes, including SOD1 and C9orf72. It does not say that the study established a new disease-causing gene.
What did the study find about sporadic disease?
Among participants recorded clinically as having sporadic disease, almost 16% of those with FTD and 5.5% of those with ALS were genetically related to another affected participant in the cohort. These are study-specific figures, not general population estimates.
Does a genetic connection mean a person will develop ALS or FTD?
No such conclusion follows from this study. It examined shared ancestry and disease-related data; it does not establish that every person carrying a shared genetic background will develop symptoms. Questions about personal genetic risk should be discussed with a qualified health professional or genetic counselor.
Source: news-medical.net
