During fetal development, the human brain generates an excess of neurons, most of which are eliminated shortly before and after birth. New research from Harvard Medical School and Boston Children’s Hospital suggests that this is a critical quality-control mechanism.

A study published Oct 28 in Nature shows that neurons with multiple copy number variants — abnormal duplications or deletions of segments of DNA — are surprisingly widespread in the developing brain. Copy number variants can impact brain function and may contribute to neuropsychiatric conditions, including autism, schizophrenia, epilepsy, and intellectual disability.

But the research also shows that the vast majority of these flawed neurons are selectively eliminated, likely because the genomic alterations disrupt their ability to form synapses.