Family studies suggest a strong genetic component to autism and schizophrenia, but the disorders are thought to arise during early development, making it difficult to study the underlying genetics.
Now researchers at Cold Spring Harbor Laboratory in New York have created mice with chromosomal abnormalities that mirror those seen in humans with these disorders, which should make it easier to study the role of genetics in the development of the brain.
In 2008, several research groups identified a section of DNA on chromosome 16 that appeared to be important for brain development in humans. Deletions of this section were tied to autism and developmental delays, while extra copies were linked to autism and schizophrenia.
The new mouse model should let scientists evaluate the effects of genetic variants at different developmental stages, starting in the womb. The hope is that these experiments will provide new clues about the biology of autism and schizophrenia and possibly identify new tests that could help clinicians diagnose these conditions. “We’re especially interested in finding early biomarkers for these disorders,” says Alea Mills, the lead author of the new study, which appears today in the Proceedings of the National Academy of Sciences.
The researchers used a relatively new genetic technique called chromosome engineering to target the mouse equivalent of the relevant section of chromosome 16. They then used standard methods to generate mice that either lacked the section or had extra copies of it.
The chromosomal deletion appeared to have more severe effects than the duplication, which is consistent with what clinicians have observed in humans. About half of the mice with the deletion died shortly after birth, suggesting that this chromosomal section is essential for proper development. Whether the deletion also contributes to infant mortality in humans is unknown.
The mice with the deletion also exhibited behaviors associated with autism, such as restricted, repetitive movements and sleep deficits. When the researchers conducted MRI scans on the mice, they found the deletion was associated with increased volume in several brain areas, particularly in the hypothalamus, the brain region that regulates eating and sleeping behaviors. The mice with the duplication tended to have smaller brain areas compared to controls, but the effect was less pronounced.
The next step for Mills and her colleagues is to figure out the mechanisms behind the behavioral and anatomical differences they observed. Most mouse models are created by manipulating a single gene, but the human and mouse versions of the chromosome 16 section each contain more than 20 genes, and it’s unclear which are the most important. “There’s going to be a need to refine this area down to fewer genes,” says David Miller, a genetics researcher at Children’s Hospital Boston who has researched the chromosome 16 deletion in humans but was not involved with this study.
Toward this end, Mills and her team are working on dividing the chromosomal section into smaller pieces and creating subgroups of their deletion and duplication in mice. Studying the interactions of so many genes will be challenging, but it may be necessary to understand complex, heterogeneous disorders such as autism and schizophrenia. Many clinics, including Children’s Hospital Boston, already have a test that can detect chromosome 16 deletions or duplications. “The trick is knowing what it means when you find them,” says Miller.