Mom's mitochondria may hold mutation
Scientists discovered in the early 1960s that mitochondria, the power-generating stations inside clls, contain a few genes of their own. Now Emory University scientists in Atlanta have linked a specific defect in mitochondrial DNA to a rare form of blindness. The discovery confirms suspicions that tainted genes in these tiny power packs can indeed cause genetic defects and suggests a whole new mechanism for inherited diseases.
Several hundred mitochondria exist in the cytoplasm of each cell, their handful of genes distinct and separate from those packed on the chromosomes inside the cell nucleus. Altogether, the mitochondria contain about 0.3 percent of a cell's total DNA. These genes code for proteins vital to the production of adenosinetriphosphate (ATP), the key fuel used by cells. Unlike the DNA in the nucleus, which comes equally from the mother and father, the genes in the mitochondria come only from the mother.
Douglas C. Wallace and his colleagues discovered that people suffering Leber's hereditary optic neuropathy (LHON) have a defect in one mitochondrial gene that codes for a protein involved in the first step of ATP production. This defect results in the amino acid histidine being substituted for the amino acid arginine during the protein's synthesis, Wallace reported this week at the Short Course in Medical and Experimental Mammalian Genetics at the Jackson Laboratory in Bar Harbor, Maine, cosponsored by johns Hopkins University in Baltimore.
LHON results in optic nerve death and often causes blindness by age 20. Since mitochondria are passed on only by the mother, if she carries the defect, every one of her children will inherit it. Yet only a minority of people who inherit the defective gene go blind, Wallace notes. …