Acytokine called tumor necrosis factor (TNF) may contribute to the development and progression of neuropsychiatric illnesses, research has suggested (Psychiatric News, March 16), and it may do so by shrinking the hippocampus, the brain’s memory center, research has also implied. Indeed, TNF is known to be located in various brain regions, including the hippocampus.

But why might TNF shrink the hippocampus? Perhaps because a variant of the gene that makes TNF tells it to do so, an imaging genetic study published online May 4 in Biological Psychiatry suggested.

The study was headed by Udo Dannlowski, M.D., Ph.D., of the Neuroimaging Research Group of the Department of Psychiatry at the University of Munster in Germany.

Dannlowski and his colleagues evaluated more than 300 subjects who were free of severe medical conditions and of a history of psychiatric disorders to see whether they possessed A or G variants of the TNF gene. The scientists found that one-third of the subjects had one A copy and one G copy or two A copies, and that the remaining two-thirds had two G copies.

The researchers then imaged the brains of the subjects and found that individuals who had one A copy and one G copy or two A copies had significantly smaller hippocampi than did those individuals with two G copies.

Thus it looks as if the A variant of the TNF gene might prompt TNF to shrink the hippocampus, the researchers reasoned, and that a shrunken hippocampus in turn might contribute to neuro-psychiatric illnesses.

Only further research, though, will demonstrate whether this is the case. “We are now investigating a group of depressed patients with the same methods. …,” Dannlowski told Psychiatric News. “We assume that also in this patient group A carriers will show abnormally reduced hippocampi and might show an earlier onset and a less benign course of illness.”

Meanwhile, other researchers have linked the A variant of the TNF gene with schizophrenia, multiple sclerosis, and an early age of onset of Alzheimer’s disease. These findings too suggest that the A variant may contribute to neuropsychiatric illnesses—although not necessarily via a shrunken hippocampus.

The study was funded by the Medical Faculty of Munster and the Rolf-Dierichs Foundation.

An abstract of “Tumor Necrosis Factor Gene Variation Predicts Hippocampus Volume in Healthy Individuals” is posted at www.biologicalpsychiatryjournal.com/article/S0006-3223(12)00310-1/abstract.