Allan Herndon Dudley syndrome

Allan-Herndon-Dudley Syndrome

Allan-Herndon-Dudley syndrome (AHDS) is a rare genetic disorder that affects the development of the nervous system and is characterized by intellectual disability and problems with movement. It is an X-linked recessive condition, meaning it primarily affects males, while females are typically carriers.

History

Allan-Herndon-Dudley syndrome was first described in 1944 by Dr. William Allan, Dr. Florence C. Dudley, and Dr. C. Nash Herndon. They reported a family with several affected males who exhibited severe intellectual disability and hypotonia.

Genetics

AHDS is caused by mutations in the SLC16A2 gene, which encodes the monocarboxylate transporter 8 (MCT8). This protein is responsible for the transport of thyroid hormones, particularly triiodothyronine (T3), into neurons. Mutations in this gene lead to impaired transport of T3, resulting in abnormal brain development and function.

Inheritance

The disorder is inherited in an X-linked recessive pattern. Males have one X chromosome and one Y chromosome, so a single mutated copy of the gene on the X chromosome is sufficient to cause the disorder. Females have two X chromosomes, so they are typically carriers if they have one mutated copy of the gene, but they usually do not show symptoms.

Clinical Features

Individuals with Allan-Herndon-Dudley syndrome typically present with:

• Severe intellectual disability
• Hypotonia (reduced muscle tone)
• Spasticity (increased muscle tone)
• Movement disorders, such as dystonia and ataxia
• Delayed motor milestones
• Dysarthria (difficulty speaking)

Diagnosis

Diagnosis of AHDS is based on clinical evaluation, family history, and genetic testing to identify mutations in the SLC16A2 gene. Thyroid function tests may show elevated levels of T3 and low levels of thyroxine (T4) and thyroid-stimulating hormone (TSH).

Management

There is currently no cure for Allan-Herndon-Dudley syndrome. Management focuses on supportive care and symptomatic treatment, including:

• Physical therapy to improve motor skills
• Occupational therapy
• Speech therapy
• Medications to manage spasticity and other symptoms

Research

Ongoing research is focused on understanding the pathophysiology of AHDS and developing potential therapies, such as thyroid hormone analogs that can bypass the defective transporter.

Also see

• X-linked recessive inheritance
• Intellectual disability
• Thyroid hormone
• Genetic disorders

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External links

• Comprehensive information from the National Institute of health.
  

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