"Nationwide, half of all unpaid Alzheimer's disease caregivers are under the age of 50 and as many as 68 percent are the children, children-in-law or grandchildren of these patients," said study author Joshua D. Grill, PhD, Assistant Professor of Neurology at the UCLA Mary S. Easton Center for Alzheimer's Disease Research and a member of the American Academy of Neurology. "In contrast, in our analyses, 67 percent of the 2,041 Alzheimer's clinical trial participants had a spouse as their study partner. We found that there were several differences between people with spouse and adult child study partners that could affect the results of the trials and interpretations of those results."

Grill adds that factors such as race and caregiver attitude may also impact recruitment to trials. For example, only five percent of participants across the trials were Hispanic and those with an adult child study partner were twice as likely as those with spouse partners to be Hispanic. In addition, six percent of participants were African-American and those with adult child study partners were nearly three times as likely to be African-American as those with spouse study partners.

For the study, the research team categorized people with Alzheimer's disease based on the type of study partner they had -- either spouse, adult child or other study partners -- from six clinical trials conducted by the Alzheimer's Disease Cooperative Study.

In addition to the differences in enrollment, they found that participants with other study partners were at increased risk to drop out of studies.

After considering other factors, the risk of dropout for the "other" study partner group was 70 percent higher than that for the "spouse" study partner group.

The study was supported by the National Institute on Aging, the Sidell-Kagan Foundation and the Marian S. Ware Alzheimer Program.

To learn more about Alzheimer's disease, visit http://www.aan.com/patients.