Hemimegalencephaly is a rare but dramatic condition in which the brain grows asymmetrically, with one hemisphere becoming massively enlarged. Though frequently diagnosed in children with severe epilepsy, the cause of hemimegalencephaly is unknown and current treatment is radical: surgical removal of some or all of the diseased half of the brain. In a paper published in the June 24, 2012 online issue of Nature Genetics, a team of doctors and scientists, led by researchers at the University of California (UC) San Diego School of Medicine and the Howard Hughes Medical Institute, say de novo somatic mutations in a trio of genes that help regulate cell size and proliferation are likely culprits for causing hemimegalencephaly, though perhaps not the only ones. De novo somatic mutations are genetic changes in non-sex cells that are neither possessed nor transmitted by either parent. The scientists' findings – a collaboration among Joseph G. Gleeson, M.D., professor of neurosciences and pediatrics at UC San Diego School of Medicine and Rady Children's Hospital-San Diego; Gary W. Mathern, M.D., a neurosurgeon at UC Los Angeles' Mattel Children's Hospital; and colleagues – suggest it may be possible to design drugs that inhibit or turn down signals from these mutated genes, reducing or even preventing the need for surgery. Dr. Gleeson's lab studied a group of 20 patients with hemimegalencephaly upon whom Dr. Mathern had operated, analyzing and comparing DNA sequences from removed brain tissue with DNA from the patients' blood and saliva. "Mathern had reported a family with identical twins, in which one had hemimegalencephaly and one did not. Since such twins share all inherited DNA, we got to thinking that there may be a new mutation that arose in the diseased brain that causes the condition," said Dr. Gleeson.
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