The study, published in the September issue of Nature Genetics, describes the gene mutation that underlies Amish microcephaly (MCPHA), a birth defect marked by a profoundly small head and brain size. Over the past 40 years, 61 babies with MCPHA have been born to 23 nuclear families in the Old Order Amish community in Lancaster County, Pa. None of the children has lived beyond the age of 14 months, and most die between 4-6 months.
In their study in Nature Genetics, the NHGRI team found the gene defect causes developing cells to lose their normal ability to transport the building blocks of DNA, called base pairs, across the inner membrane walls of the mitochondria, which are tiny structures that function as the cells' metabolic power houses. Researchers believe that without this carrying ability, called mitochondrial deoxynucleotide transport, the cell's mitochondria cannot make DNA properly, causing the brain of the unborn child to develop abnormally. The NHGRI data also indicate that mitochondrial deoxynucleotide transport may play a crucial role in normal prenatal brain growth.
"It's a significant finding to all prenatal brain development," says Dr. Leslie Biesecker, the study's lead author and a senior investigator for the Genetic Disease Research Branch at NHGRI. "It makes a tie between energy metabolism and brain development."
Five other genes have been linked the brain-development abnormalities, including one called ASPM that appears to cause microcephaly in the children of a large family from Pakistan. Microcephaly can also be caused by the chromosomal disorder, trisomy 21 Down syndrome, and by environmental factors, such as fetal alcohol syndro
Contact: Geoff Spencer
NIH/National Human Genome Research Institute