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A study in Brain used DNA data from 3,524 people with ALS or frontotemporal dementia to identify 793 related pairs, including many relationships not previously recognized. The findings created 73 DNA-based family trees and connected some people whose disease had been recorded as sporadic, offering researchers a way to investigate inherited risk that family histories may miss.
Researchers from the Macquarie University Brain Institute and Clinic have identified hundreds of previously unrecognized genetic relationships among people with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The study, based on DNA data from 3,524 people in Australia, New Zealand and the United Kingdom, found 793 related pairs and used the hidden connections to build 73 DNA-based family trees that may help researchers search for disease-linked genes.
The team applied a method called cryptic relatedness analysis to identify people who shared inherited DNA, including relatives as distant as third cousins. More than 30 per cent of the relationships identified had not been recognized previously, according to the study report. The analysis drew on people with FTD and motor neuron disease, also known as ALS.
The newly reconstructed family trees came from people who had no known genetic explanation for their disease. Finding affected relatives gives researchers more people to compare: shared stretches of DNA can help narrow the search for variants that may be involved. The study also mapped shared ancestry around known ALS and FTD genes, including SOD1 and C9orf72, identifying networks in which people carried the same genetic change inherited from a distant common ancestor.
The findings also complicate the usual distinction between familial and sporadic disease. Among people whose cases were clinically recorded as sporadic, nearly 16 per cent of those with FTD and 5.5 per cent of those with ALS were genetically related to another affected person in the cohort. Some related people had different diagnoses, the report said. These results describe patterns within this study group; they do not establish that every identified connection caused disease or predict an individual’s outcome.
Adult-onset disease can make inherited patterns hard to see. A person may carry a disease-associated genetic variant without developing symptoms, while family records may be incomplete or relatives may not know of one another. DNA-based links can reveal shared ancestry even when a conventional family history does not point researchers toward a connection.
For gene discovery, the practical value is a larger set of relatives to compare. When more than one affected person shares DNA inherited from a common ancestor, researchers can look for genetic regions shared among them and prioritize candidates for further study. The study’s authors say this approach could make better use of existing patient cohorts, but the reported family links are a research tool—not a new diagnostic test or a guarantee that a specific disease gene will be found.
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Why Family History Can Miss Links
ALS affects motor neurons, while FTD is a group of disorders involving changes in behavior, personality or language. The conditions can have genetic causes, and some genetic backgrounds are associated with either or both diagnoses. However, not all cases have an identified genetic explanation, and relatives who share a risk variant may not show the same symptoms.
The study, led by Dr. Lyndal Henden with Professor Kelly Williams as senior author, used identity-by-descent analysis to find DNA inherited from shared ancestors. Its paper, “Identity-by-descent to resolve reduced penetrance and advance gene discovery in neurodegenerative disease,” was published in the journal Brain in 2026. The research examined a combined cohort from three countries; its results should be understood within that study population.
“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
What the DNA Links Cannot Show
The analysis identified shared ancestry, but a genetic relationship alone does not establish which inherited variant, if any, caused a person’s illness. The report does not show that all 793 related pairs shared a disease-causing mutation, and the study’s findings cannot be used to estimate an individual’s risk from the figures alone.
It is also not clear from the reported results how many new disease-causing genes the family trees will ultimately help identify, or whether the method will produce similar findings in other populations. Some relatives may remain undiagnosed, and reduced penetrance means people with a relevant genetic variant may not develop symptoms. The study reports associations and research opportunities, not a clinical prediction for families.
How Researchers May Use the Trees
The next research step is to compare DNA across the newly assembled families and investigate candidate regions for variants linked to ALS or FTD. Researchers can also examine the mapped networks around known genes, including SOD1 and C9orf72, to better understand shared ancestry and differences in diagnosis or symptoms.
The study does not specify a timetable for follow-up results. Any future gene findings would need further investigation before their role in disease could be established. For now, the reported advance is the ability to identify hidden relationships in existing cohorts and use those connections to guide further genetic research.
Key Questions
What did the researchers discover?
Using DNA data from 3,524 people with ALS or FTD, researchers identified 793 related pairs and built 73 DNA-based family trees from people whose disease had no known genetic explanation.
What is cryptic relatedness analysis?
It is a method for detecting people who share inherited DNA and are genetically related, even when their connection is not known from family records. In this study, identified relatives ranged from siblings to third cousins.
Does this mean ALS and FTD are the same disease?
No. The study found genetic connections across people diagnosed with the two conditions, and some related individuals had different diagnoses. It does not say that ALS and FTD are the same disease.
What does the study say about sporadic cases?
Within this cohort, nearly 16 per cent of people with FTD and 5.5 per cent of people with ALS whose disease was recorded as sporadic were genetically related to another affected person in the study. Those figures apply to the research group and do not determine an individual’s diagnosis or risk.
Can the findings predict a person’s risk?
No. The study maps relationships and supports research into disease-associated genes; it does not provide an individual risk assessment. People with questions about genetic testing or family risk should speak with a qualified health professional or genetic counsellor.
Source: news-medical.net
