OPA3 — Outer mitochondrial membrane lipid metabolism regulator OPA3

The OPA3 gene contains the instructions for making a protein that lives in your mitochondria, which are the "power plants" of your cells. This protein helps keep the mitochondria in the right shape and working properly so they can produce enough energy. It is especially important for cells that need a lot of energy, like the nerve cells in your eyes and brain. When there is a mutation (a change or mistake) in the OPA3 gene, the mitochondria become disorganized and cannot produce energy efficiently. Because the nerve cells in your eyes (retinal ganglion cells) rely heavily on this energy, they can become damaged and die. This leads to a condition called optic atrophy, which causes a gradual loss of vision. Some people may also develop cataracts, which is a clouding of the lens in the eye. Depending on the type of mutation, it can be passed down from one parent (autosomal dominant) or both parents (autosomal recessive). In the recessive form, known as Costeff syndrome, the lack of energy also affects the brain, leading to movement problems, muscle stiffness, and developmental delays in addition to vision loss.

Gene description: The OPA3 gene provides instructions for making a protein found in mitochondria, the energy-producing centers of cells. It plays a role in regulating mitochondrial morphology, fission, and lipid metabolism, and is essential for the survival of cells with high energy demands, such as retinal ganglion cells.

Patient and family guide: The OPA3 gene contains the instructions for making a protein that lives in your mitochondria, which are the "power plants" of your cells. This protein helps keep the mitochondria in the right shape and working properly so they can produce enough energy. It is especially important for cells that need a lot of energy, like the nerve cells in your eyes and brain. When there is a mutation (a change or mistake) in the OPA3 gene, the mitochondria become disorganized and cannot produce energy efficiently. Because the nerve cells in your eyes (retinal ganglion cells) rely heavily on this energy, they can become damaged and die. This leads to a condition called optic atrophy, which causes a gradual loss of vision. Some people may also develop cataracts, which is a clouding of the lens in the eye. Depending on the type of mutation, it can be passed down from one parent (autosomal dominant) or both parents (autosomal recessive). In the recessive form, known as Costeff syndrome, the lack of energy also affects the brain, leading to movement problems, muscle stiffness, and developmental delays in addition to vision loss.

Gene function: The OPA3 protein is an integral protein of the mitochondrial outer membrane. It is thought to play a crucial role in the organization of the shape and structure of mitochondria, inducing mitochondrial fragmentation (fission), and regulating lipid metabolism. It is also involved in controlled cell death (apoptosis).

Protein structure: OPA3 is a 179-amino acid protein (approximately 20-kDa) that contains a mitochondrial targeting peptide at its N-terminus. It is an integral protein of the mitochondrial outer membrane, with its C-terminus exposed to the cytosol and its N-terminal region anchored in the membrane.

Molecular function: At the molecular level, OPA3 acts as an integral protein of the mitochondrial outer membrane. It regulates mitochondrial lipid metabolism and is involved in mitochondrial dynamics, specifically inducing mitochondrial fragmentation or fission. By maintaining the proper shape and structure of the mitochondrial network, OPA3 ensures efficient energy production. It also plays a role in the apoptotic pathway, influencing the susceptibility of cells to controlled cell death, particularly in tissues with high metabolic rates like the optic nerve and brain.

Mutation spectrum: Mutations in the OPA3 gene include missense mutations (e.g., Gln105Glu or Q105E), which are common in autosomal dominant optic atrophy and cataract. Splice site mutations (e.g., c.143-1G>C) are found in Costeff syndrome, leading to a complete loss of functional protein. Nonsense mutations and deletions may also occur.

Clinical significance: Mutations in the OPA3 gene lead to abnormal mitochondrial function. The mitochondria become misshapen, disorganized, and have reduced energy-producing capabilities. Cells with these poorly functioning mitochondria, particularly those with high energy demands like retinal ganglion cells, are more susceptible to apoptosis. The death of retinal ganglion cells causes optic nerve atrophy, leading to vision impairment. In Costeff syndrome, complete loss of OPA3 function also affects nerve cells in the brain, resulting in movement problems and delayed development.

Inheritance: Autosomal Dominant, Autosomal Recessive

Chromosomal location: 19q13.32

Research and therapeutic approaches: Currently, there are no specific gene therapies or targeted treatments for OPA3-related conditions. Management is supportive and multidisciplinary, focusing on treating symptoms. This includes cataract surgery, low vision aids, physical and occupational therapy for motor disabilities, and hearing aids for sensorineural hearing loss.