What is 4H leukodystrophy? 

4H leukodystrophy is a rare genetic disorder that affects the nervous system. The name is short for hypomyelination with hypogonadotropic hypogonadism and hypodontia. The condition is also known as 4H syndrome or Polr 3-related leukodystrophy.

Leukodystrophy is a group of conditions that affect the white matter of the brain. These diseases damage the myelin sheath, which surrounds and protects the nerve cells in the brain and spinal cord and speeds transmission of messages between cells.

The process of the body forming this protective myelin sheath is called myelination. Typically, myelination develops in the first few years of life. Hypomyelination means that the body is unable to produce myelin at normal levels. This prevents the body from completing normal myelination of the brain, and in some cases, the nerves outside the brain.

4H leukodystrophy is the combination of that myelin deficiency and two other conditions: hypogonadotropic hypogonadism (a condition that results in delayed puberty) and hypodontia (having fewer teeth than normal or an abnormal development of those teeth).

People with 4H leukodystrophy often have motor problems, including stiffness of the muscles and joints and problems with balance and coordination. They may also have movement disorders, including tremor or difficulty controlling smooth movements of their arms and legs. As infants, they may have delay in teething or have teeth appear in an unusual order. They are usually small for their age, and they do not go through typical puberty.