Corticosterone Methyloxidase Type 2 Deficiency (CMO II): A Patient Guide

Corticosterone Methyloxidase Type 2 (CMO II) deficiency is a rare, inherited condition that affects how the adrenal glands produce a vital hormone called aldosterone. Often referred to as Aldosterone Synthase Deficiency Type II, this disorder prevents the body from performing the final step in creating the hormone responsible for maintaining salt and water balance ^[1]. Without enough aldosterone, infants begin to lose excessive amounts of sodium in their urine, a process known as salt-wasting, which can lead to life-threatening dehydration and high levels of potassium in the blood if not recognized and treated early ^[2].

The condition typically reveals itself within the first few months of life, often presenting as a “failure to thrive.” Parents may notice their infant is persistently fussy, vomiting, or struggling to gain weight despite regular feedings ^[3]. These early signs are the body’s way of signaling that its internal chemistry is out of balance. While these symptoms can be frightening, identifying them allows medical teams to start targeted treatments to stabilize the child’s electrolytes and restore their health ^[4].

One of the most important things for families to understand is that isolated CMO II is distinct from many other adrenal disorders, such as classic salt-wasting Congenital Adrenal Hyperplasia (CAH). In confirmed, isolated CMO II, the production of cortisol—the body’s primary stress-response hormone—usually remains preserved ^[2]. While this means routine stress-dose steroids are often unnecessary once the diagnosis is confirmed, it does not mean a salt-wasting crisis is harmless ^[5]. Untreated dehydration and electrolyte imbalances remain a severe medical emergency, and families must always follow their endocrinologist’s specific sick-day plan ^[2].

Standard treatment consists of replacing the missing hormone effect with a medication called fludrocortisone and providing a precisely prescribed liquid salt supplement ^[6]. Once this balance is restored, many infants experience a period of “catch-up growth,” though the exact timeline varies depending on the child ^[3].

As children grow, their kidneys often become more efficient at retaining salt naturally, which may allow for a reduction in medication doses as they reach school age ^[3]. However, this is not a guarantee for every child, and any medication changes must be part of a carefully supervised medical trial ^[4]. By working closely with a pediatric endocrinologist and maintaining a consistent monitoring schedule, families can ensure their children stay healthy, safely hydrated, and well-balanced throughout every stage of their development ^[3].