"People with a mother with Alzheimer's disease had signs of brain shrinkage similar to people with early Alzheimer's," says researcher Robyn Honea, DPhil, an assistant professor of neurology at the University of Kansas School of Medicine.
Those with a maternal family history, she says, had twice as much gray matter shrinkage, which occurs with the disease, per year as those who had either a father with the disease or no parental history of it.
But a spokeswoman for the Alzheimer's Association who reviewed the findings takes exception to them, saying the sample size of 53 people is too small to come to any credible conclusions.
The study, supported by the National Institute on Aging and the National Institute of Neurological Disorders and Stroke, is published in the journal Neurology.
About 5.3 million Americans have Alzheimer's disease, according to estimates from the Alzheimer's Association.
Alzheimer's Disease & Maternal History: Study Details
Of those 53 people Honea evaluated, all were over age 60 and cognitively healthy at the start. There were 11 with a maternal family history, 10 with a paternal history, and 32 with no parental history of Alzheimer's.
Age is considered the most significant risk factor for developing Alzheimer's, Honea writes. Research has shown that first-degree relatives are at a fourfold to tenfold higher risk of getting the disease compared to those with no family history, and some other research has found a mother's history of the disease riskier for offspring than a father's history.
At the study start, all three groups were given a battery of tests to measure memory, language, and cognitive skills. They were given brain MRIs.
At 24 months, the tests and the scans were repeated and the researchers looked at brain shrinkage, which occurs with the disease.
- Those with a mother with Alzheimer's disease had about 1.5 times more brain shrinkage per year than those with a father with the disease.
- Those with a mother with Alzheimer's had twice the gray matter shrinkage as those who had no parental history or a father with the disease.
- The performance on the cognitive tests did not change at two years.
''We were surprised that a group that seemed healthy could start to have shrinkage in these areas," Honea tells WebMD.
The new findings echo some of previous studies finding a maternal family history linked with higher risk than a paternal history, she says. "Our research is adding to this data signaling there is something specific inherited from the mother."
Honea controlled for such factors as age and gender and the link held. The link held, too, when she took into account the presence of the ApoE4 gene, which is linked to an increased risk for Alzheimer's disease.
While 63% of those with a maternal family history were ApoE4 carriers, 20% of those with a paternal history were and 15% of those lacking a family history were.
Mother With Alzheimer's Disease: Why the Stronger Link?
Why the stronger link with a mother's history of Alzheimer's is not known, she says. "Our hypothesis is that is has something to do with mitochondrial DNA, which is only passed through the mother," she says. ''That is not to say that this is the only mechanism at play. We think there are multiple genetic mechanisms."
While most DNA is packaged in the chromosomes, mitochondria (the so-called energy powerhouses of cells) also have a small amount of DNA.
Honea reports no disclosures, but her co-authors do. Russell Swerdlow, MD, has served on speakers' bureaus for Pfizer and Accera; received speaker honoraria from Medivation Inc. and Accera, and research support from Medivation.
Jeffrey Burns, MD, serves on the speakers' bureau for Pfizer Inc. and Novartis and has been a consultant for Medacorp Consulting, Johnson County Clinical Trials, and PRA International, and has research support from Elan Corporation, Janssen, Wyeth, Pfizer, Danone, and others.
Alzheimer's Disease and Maternal History: Questions Remain
Maria Carrillo, PhD, the senior director of medical and scientific relations for the Alzheimer's Association, reviewed the study findings for WebMD.
In a statement, she says that ''the sample is simply too small to come to any real conclusions."
"While the results are somewhat consistent with previous findings regarding possible maternal genetic influence on Alzheimer's risk, this study was done on such a small scale that we would hesitate to call this a replication. This influence of maternal genetic contribution to Alzheimer's risk is still very much an unsettled question."
Until more research is done, the Alzheimer's Association recommends efforts to prevent or delay Alzheimer's, such as getting regular exercise, eating a heart-healthy diet, getting intellectual stimulation, and staying socially engaged.