What is Allan-Herndon-Dudley Syndrome (AHDS)?

Allan-Herndon-Dudley syndrome (AHDS) is an extremely rare inherited disorder of brain development. The disorder results in moderate to severe mental retardation. Problems with movement and muscle tone problems are also characteristic of AHDS. Because of these problems, people affected by AHDS have a hard time communicating and are usually wheelchair-bound by early adulthood. People with AHDS do not have any distinct physical characteristics, however, elongation of the face and abnormal folding of the ears is usually present.

Who gets AHDS?

AHDS is rare. There are more than thirty families with confirmed cases of the condition. Although the exact prevalence is not known, it appears it may affect as many as one in ten-thousand males. The condition is inherited in an X-linked recessive manner. Because of this, only males can get AHDS and only females can be carriers. AHDS is always present at birth and development was disrupted far before birth, however, the condition may not be apparent for months following birth.

What causes AHDS?

AHDS is caused by a mutation of the SLC16A2 gene, also known as MCT8. SLC16A2 provides instructions for making SLC16A2 protein, a protein responsible for transporting triiodothyronine, or T3, into nerve cells during brain development. T3 has many critical roles in the body including playing a part in normal formation and growth of nerve cells.

Because of the mutation of the SLC16A2 gene, brain development is disrupted. Since T3 is not being used by nerve cells, there are excessive amounts of the hormone in the blood causing toxicity and further contributing to the symptoms of AHDS.

What are the symptoms of AHDS?

Infants with AHDS usually appear healthy at birth. Within a few months, however, symptoms of the disorder begin to appear. These include poor muscle tone, inability to hold up the head, and physical and mental developmental delays. Children with AHDS may never be able to walk. They also have difficulty developing language. As the child ages, more symptoms appear. These include severe physical and mental delays, mental retardation, muscle weakness and stiffness, exaggerated reflexes, movement abnormalities, joint deformities, involuntary movements of the limbs, and impaired speech.

How is AHDS diagnosed?

Diagnosis of AHDS is reached once other conditions have been ruled out. A physical examination, medical history, and numerous tests can aid in diagnosis. There is genetic testing available, however, it has proved unsuccessful in some cases. Therefore, it is not always relied upon.

How is AHDS treated?

There is no cure for AHDS nor is there any specific treatment. Treatment is highly individualized. Because patients are usually severely cognitively impaired, special education and structured care is needed. Physical therapy appears to help with some movement problems. Since most of the mental damage associated with AHDS occurs before birth, early intervention is not successful.

What is the prognosis of those with AHDS?

Prognosis of AHDS is good. There does not appear to be an increased risk for any health effects. Therefore, AHDS patients live relatively long lives.

Source

WebMD

National Library of Medicine