Researchers have discovered a boy born without an entire set of brain cells.

Documented in the American Journal of Human Genetics, James Bennett from the University of Washington reported treating an infant with a gene mutation, born with multiple congenital brain abnormalities.

The baby was brought from rural Alaska to Bennett, a paediatric geneticist in Seattle, in the hope that he would be able to uncover the reason for the abnormalities - but the findings were far stranger than the doctor had anticipated.

The baby had trouble breathing, was unable to eat properly, and suffered from epilepsy. He died from a bacterial infection at 10 months of age.

"There wasn't any part of the brain that wasn't involved and affected in this child," Bennett told The Atlantic.

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During his autopsy, the researchers found no microglia in his brain - which is why it had grown to fill his skull incorrectly, and jutted out on an angle.

"Things get off track pretty quickly when you start manipulating the functions of microglia," said Stephen Noctor, a developmental neurobiologist at the University of California.

The autopsy also revealed that he carried two copies of CSF-1R, as his parents, who were cousins, each carried a single copy of the gene.