The largest study to date of twins and Alzheimer’s disease indicates that inheritance may play a role in nearly 80 percent of cases, researchers said on Monday.

The report from the University of Southern California was based on a look at 392 pairs of twins in Sweden, age 65 and beyond, both identical and fraternal, at least one of whom had been diagnosed with Alzheimer’s. They were compared to a similar group of twins who were free of the disease.

While genetics has already been linked to the disease the new research “confirms the higher estimates that have been suggested previously. The important thing is that no one has had this large a sample before,” said lead author Margaret Gatz. She said the sample was 10 times larger than any other group of twins studied for the disease.

Gatz said the study “does suggest that there is an underlying genetic basis” but she cautioned “this doesn’t mean that environment is not important. Environment may be relevant not only for whether but also for when one gets the disease.”

The study, published in the Archives of General Psychiatry, concluded that heritability was “79 percent in the best fitting (analytical) model with the balance of variation explained by non-shared environmental influences.”

In a second study published in the same journal, researchers at Mount Sinai School of Medicine, New York, found that people who suffer from depression throughout their life and later develop Alzheimer’s show more physical changes in their brain than those with the disease who did not have depression.

Those with depression also suffer a more rapid mental decline once they develop the disease, said the study which was based on more than 90 Alzheimer patients, some of whom had lifetime depression and others who did not.

Previous studies have linked depression and Alzheimer’s disease, the study added.