What are the genetic changes related to pseudohypoaldosteronism type 1 ?
Mutations in one of four different genes involved in sodium regulation cause autosomal dominant or autosomal recessive PHA1. Mutations in the NR3C2 gene cause autosomal dominant PHA1. This gene provides instructions for making the mineralocorticoid receptor protein. Mutations in the SCNN1A, SCNN1B, or SCNN1G genes cause autosomal recessive PHA1. Each of these three genes provides instructions for making one of the pieces (subunits) of a protein complex called the epithelial sodium channel (ENaC).  The mineralocorticoid receptor regulates specialized proteins in the cell membrane that control the transport of sodium or potassium into cells. In response to signals that sodium levels are low, such as the presence of the hormone aldosterone, the mineralocorticoid receptor increases the number and activity of these proteins at the cell membrane of certain kidney cells. One of these proteins is ENaC, which transports sodium into the cell; another protein simultaneously transports sodium out of the cell and potassium into the cell. These proteins help keep sodium in the body through a process called reabsorption and remove potassium from the body through a process called secretion.  Mutations in the NR3C2 gene lead to a nonfunctional or abnormally functioning mineralocorticoid receptor protein that cannot properly regulate the specialized proteins that transport sodium and potassium. As a result, sodium reabsorption and potassium secretion are both decreased, causing hyponatremia and hyperkalemia.  Mutations in the SCNN1A, SCNN1B, and SCNN1G genes result in reduced functioning or nonfunctioning ENaC channels. As in autosomal dominant PHA1, the reduction or absence of ENaC function in the kidneys leads to hyponatremia and hyperkalemia. In addition, nonfunctional ENaC channels in other body systems lead to additional signs and symptoms of autosomal recessive PHA1, including lung infections and skin lesions.