Which are the symptoms of Allan-Herndon-Dudley Syndrome?

Allan-Herndon-Dudley Syndrome (AHDS) is a rare genetic disorder that primarily affects the development and function of the brain. It is an X-linked recessive disorder, meaning it primarily affects males. This syndrome is caused by mutations in the SLC16A2 gene, which is responsible for producing a protein called monocarboxylate transporter 8 (MCT8). MCT8 plays a crucial role in transporting thyroid hormones into the brain.

The symptoms of Allan-Herndon-Dudley Syndrome can vary in severity, but they generally become apparent in early infancy. Infants with AHDS may exhibit delayed development, particularly in motor skills such as sitting, crawling, and walking. They may have weak muscle tone (hypotonia) and experience difficulty with coordination and balance. These motor impairments can lead to delayed or absent speech development.

Individuals with AHDS often have intellectual disability. The severity of intellectual impairment can range from mild to severe. They may have difficulty with learning, problem-solving, and understanding abstract concepts. Additionally, individuals with AHDS may have poor attention span and exhibit hyperactivity.

Another prominent symptom of AHDS is abnormal muscle stiffness (spasticity). This can cause muscle tightness and involuntary muscle contractions (spasms). The stiffness primarily affects the legs, making walking and other movements challenging. Some individuals may require assistive devices such as braces or wheelchairs for mobility.

Individuals with AHDS may also experience problems with speech and language. They may have limited vocabulary, difficulty articulating words, and struggle with grammar and syntax. Communication difficulties can further contribute to social and behavioral challenges.

Other common features of AHDS include:

• Abnormalities in muscle tone, such as hypotonia (low muscle tone) in infancy and spasticity (high muscle tone) in later childhood


• Delayed or absent growth, resulting in short stature


• Distinct facial features, including a prominent jaw, a wide mouth, and a large tongue


• Abnormalities in the structure of the brain, which can be observed through neuroimaging studies


• Seizures, which may vary in frequency and severity


• Abnormalities in thyroid hormone levels

It is important to note that the symptoms and their severity can vary among individuals with AHDS. Some individuals may have milder symptoms and better functional abilities, while others may experience more significant impairments. Due to the rarity of AHDS, it is crucial for affected individuals to receive comprehensive medical care and support from healthcare professionals familiar with the syndrome.