A higher risk of Alzheimer disease was associated with early risers, a new study published in Neurology reports. The study found no link between major depressive disorder and Alzheimer disease.

Although previous studies report comorbidity of depressive disorders and neurodegenerative diseases such as Alzheimer disease, the researchers wanted to find out if a causal relationship exists between them as well as between Alzheimer disease and other abnormal sleep patterns.

The researchers conducted a bidirectional two-sample Mendelian randomization (MR) study. A genome-wide association study used data from the UK Biobank, the Psychiatric Genomics Consortium database, and the International Genomics of Alzheimer’s Project.

The authors found no causal relationship between major depression and sleep-related phenotypes, nor did they find statistically significant relationships between major depression and Alzheimer disease.


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“Morning people” had genetically higher risks of Alzheimer disease, a lower risk of insomnia, and shorter sleep duration. They were also less likely to report long sleep. They also found people with higher risk of Alzheimer disease generally have a lower risk of insomnia.

Limitations include the fact that MR may overestimate the effect of clinical intervention on outcomes. In addition, the researchers obtained data only from middle-age or older individuals.

“Future work could explore the genetic heterogeneity of depression syndromes to test for causal relationships between potentially aetiologically distinct sub-types of depression (eg, late-onset depression) and Alzheimer’s disease,” the researchers concluded.

Reference

Huang J, Zuber V, Matthews PM, Elliott P, Tzoulaki J, Dehghan A. Sleep, major depressive disorder, and Alzheimer disease: A Mendelian randomization study. Neurology. 2020 Oct 6;95(14):e1963-e1970. doi: 10.1212/WNL.0000000000010463