What causes Opitz G/BBB syndrome ?
What causes Opitz G/BBB syndrome? The X-linked form of Opitz G/BBB syndrome is caused by mutations in the MID1 gene. The MID1 gene provides instructions for making a specific protein called midline-1. This protein helps regulate the function of microtubules, which are rigid, hollow fibers that make up the cell's structural framework (the cytoskeleton). Microtubules help cells maintain their shape, assist in the process of cell division, and are essential for the movement of cells (cell migration). The MID1 gene is a member of a group of genes called the TRIM (tripartite motif) family. The proteins produced from this large family of genes are involved in many cellular activities. Primarily, TRIM proteins play a role in the cell machinery that breaks down (degrades) unwanted proteins. As part of its protein degrading function, midline-1 is responsible for recycling certain proteins, including phosphatase 2A (PP2A), integrin alpha-4 (ITGA4), and serine/threonine-protein kinase 36 (STK36). The recycling of these three proteins so they can be reused instead of broken down is essential because they are needed for normal cellular functioning. Mutations in the MID1 gene lead to a decrease in midline-1 function, which prevents this protein recycling. As a result, certain proteins are not recycled, and they accumulate in cells. This buildup impairs microtubule function, resulting in problems with cell division and migration. Researchers speculate that the altered midline-1 protein affects how the cells divide and migrate along the midline of the body during development, resulting in the features of Opitz G/BBB syndrome. Some people who have a family history of X-linked Opitz G/BBB syndrome have no detectable MID1 mutation. The reason for this is not yet known, although some researchers have suggested the involvement of other unknown genes. The autosomal dominant form of Opitz G/BBB syndrome is caused by a deletion of a small piece of chromosome 22, specifically 22q11.2, which is why researchers consider this condition to be part of 22q11.2 deletion syndrome. It is not yet known which deleted gene(s) within this region of chromosome 22 specifically cause the signs and symptoms of Opitz G/BBB syndrome. In others with autosomal dominant Opitz G/BBB syndrome, the cause is related to a mutation in the SPECCIL gene. Click on the gene name to learn more about its role in the development of this condition.