What causes McCune-Albright syndrome (MAS)?

MAS is a genetic disorder, which means that a change, also called a mutation, in a gene causes it. Genes are in the chromosomes of almost all human cells, and they code for each cell’s specialized actions. The mutation that causes MAS leads to errors in the functioning of certain cells.¹

MAS is not an inherited disease, meaning parents do not pass it on to their child, because the mutation occurs randomly while an embryo is developing.

GNAS Gene Mutation

MAS is caused by a mutation in the GNAS gene. The GNAS gene codes for one part of the G protein, which is short for guanine nucleotide-binding protein. This protein plays an important role in triggering many other cell processes. One of these processes is to turn off an enzyme called the adenylate cyclase enzyme. The mutated form of the G protein cannot turn this enzyme off, so the constantly active adenylate cyclase enzyme causes excess production of other hormones, resulting in the symptoms of MAS.¹

Mosaicism

The GNAS mutation happens after an embryo begins to form, and not when the mother’s egg or the father’s sperm is formed. Therefore, not all of the embryo’s cells have the mutation. This is called mosaicism. The severity of MAS symptoms depends on the number and location of cells containing the mutated GNAS gene.¹

MAS is caused by a mutation in the GNAS gene. The mutation leads to errors in the functioning of certain cells.¹

The GNAS gene codes for one part of the G protein, which is short for guanine nucleotide-binding protein. This protein plays an important role in triggering many cell processes, including the process that "turns off" an enzyme called the adenylate cyclase enzyme. The mutated form of the G protein cannot turn off the enzyme. High levels of active adenylate cyclase cause excess production of other hormones, resulting in the symptoms of MAS.¹

Not every cell in the body is exactly the same, so some cells may have the GNAS mutation while others do not. This is called mosaicism. The severity of MAS symptoms depends on the number of cells with the mutated GNAS gene and the location of those cells in the body.¹