Hikikomori, The Extreme Self-Isolation Syndrome, Can Be Seen In The Blood - IFLScience

We all have those days when we just don't want to face the world – but what if that feeling never went away? What if it lasted for six months or more? That's the condition known as "hikikomori," or pathological social withdrawal. It's estimated to affect as many as a million people in Japan, and recent years have seen the phenomenon go global. But what causes this extreme self-isolation? A new study out of Kyushu University may have some answers.

"Mental illnesses such as depression, schizophrenia, and social anxiety disorder are occasionally observed in hikikomori individuals," explained Kyushu neuropsychiatry researcher Takahiro Kato. "However, our past research shows that it is not that simple, and that it is a complex condition with overlaps of different psychiatric and non-psychiatric elements."

Kato is the lead author of the study, which was published this week in the journal Dialogues in Clinical Neuroscience. Its main conclusion: there are a number of physical markers observable in the blood of individuals experiencing hikikomori, which researchers can use to distinguish between those with and without the illness – and even determine how severe their condition is.

"Understanding what happens biologically will help us greatly in identifying and treating hikikomori," Kato said.

Hikikomori first started gaining attention in the 1990s, then attributed to Japan's economic stagnation and culture of shame, but since then it has grown into a distinct phenomenon. Kyushu University has traditionally been ahead of the curve, though, opening the world's first outpatient clinic for hikikomori research in 2013.

The hope was to study the condition through a multi-faceted lens, developing support systems for patients through biological, psychological, and social perspectives on the phenomenon. While research has learned a lot about the sociological causes of hikikomori, there has been much less progress when it comes to the biological aspects of the syndrome.

Not so anymore. The team recruited 42 unmedicated hikikomori individuals and 41 healthy volunteers, and analyzed detailed data on their plasma metabolomes – the name for the small molecules found in our blood such as sugars, amino acids, and proteins, the team explain.

"Some of our key findings showed that, in the blood of men with hikikomori, ornithine levels and serum arginase activity were higher while bilirubin and arginine levels were lower," said first author Daiki Setoyama. "In both men and women patients, long-chain acylcarnitine levels were higher."

If you're familiar with biological markers in mental illness, those names were likely setting off some alarm bells. Ornithine, for example, is an amino acid associated with many bodily functions, but in particular, it helps regulate blood pressure. Bilirubin is usually talked about in relation to liver function, but it also has a peculiar connection to depression. Acylcarnitines play an important role in supplying energy to the brain, with levels in patients with depression decreasing when they take certain treatments for the condition.

All of which add up to the start of a rather convincing biological explanation for hikikomori. "When this data was further analyzed and categorized, we were able to distinguish between healthy and hikikomori individuals, and even predict its severity," said Setoyama.

If some experts are to be believed, the findings couldn't be more relevant. After more than two years of living under various lockdowns and pandemic measures, some fear that hikikomori may be turning up in places outside Japan.

"Today, hikikomori is spreading worldwide, thus, we must conduct international investigations to understand the similarities and differences between patients with hikikomori globally," said Kato.

"Identifying the biomarkers of hikikomori is the first step in uncovering the biological roots of the condition and connecting them to its severity," he concluded. "We hope these findings will lead to better specialized treatments and support for hikikomori."