Study: Autism-Linked Gene Deletion Could Affect Cognitive Speed

Myelin, a sheath of insulation around nerves that helps electrical impulses travel through the central nervous system, is reduced in mice that have a gene deletion associated with autism spectrum disorder (ASD), results of a study by the University of Texas Health Science Center at San Antonio show.¹

Investigators depleted 1 copy of a gene, Tbx1, which is encoded in the chromosome 22q11.2 region linked to impaired cognition, to find cognitive speed was slower in those mice on 2 tests: attentional set shifting, which challenges cognitive flexibility, and the Morris water maze, which taxes spatial memory.¹

"Variants of this gene, Tbx1, are associated with ASD, intellectual disability, and many other developmental issues," Noboru Hiroi, PhD, professor of pharmacology at UT Health San Antonio, said in a statement. "These ultra-rare variants are found in only a few families in the world."¹

UT Health San Antonio investigators teamed up with investigators from Tohoku University in Japan, who performed whole-brain magnetic resonance imaging studies to discover which brain regions had altered white matter.¹

Changes were seen only in the fimbria, a band of nerve fibers that connect various brain regions with the hippocampus, which is the center of learning and memories.¹

"That is a very regionally specific deficit," Dr. Hiroi said.¹

The findings were confirmed by investigators through electron microscopy.¹

In analyzing the slower cognition exhibited by the mice, the investigators hypothesized that myelin was negatively affected.¹

Indeed, mice lacking 1 Tbx1 copy did not have as many cells called oligodendrocytes, which are the cells that manufacture myelin.¹

"This negatively affected the production of the building blocks of myelin, which resulted in these mice not having enough protective fibers," Hiroi said. "Without the myelin sheath, you don't have speedy signal conductance between brain regions."¹

The study is limited, because investigators cannot compare the speed of mice on a pair of tests with actual cognition in humans.¹

However, human and mice studies are both important in understanding gene copy number variants in developmental and psychiatric disorders,” Hiroi said.¹

"In a mouse model, we identified structural changes in the brain and a specific gene that, when deficient, is responsible for those changes," Hiroi said.

"Tbx1 is only one of many genes implicated in autism and schizophrenia, but this mechanistic basis we found, this impaired myelination, can be tested for generalizability in other copy number variants and ultra-rare variants.¹

The study was funded by 3 institutes of the US National Institutes of Health: Institutes of Health: the Eunice Kennedy Shriver National Institute of Child Health and Human Development; the National Institute of Mental Health, and the National Institute on Deafness and Other Communication Disorders.¹

ASD affects 1 in 44 children, according to the CDC.²

References

1. Autism-linked gene, if deleted, results in less myelin. Science Daily. News release. December 21, 2021. Accessed January 5, 2022. https://www.sciencedaily.com/releases/2021/12/211221102655.htm

2. Data & statistics on autism spectrum disorder. CDC. Updated December 2, 2021. Accessed January 6, 2022. https://www.cdc.gov/ncbddd/autism/data.html