Allan-Herndon-Dudley syndrome
Allan-Herndon-Dudley syndrome is a rare inherited disorder affecting the brain development. This occurs mainly among the male population who exhibit moderate to severe mental disabilities and problems with their movements. Although the infants born with this condition appear normal, the symptoms become evident shortly after birth and include poor muscle tone, inability to control head movements and developmental delays. This rare condition has only been reported in about 25 families affecting 89 individuals globally.
Symptoms
The children affected with allan-herndon-dudley syndrome are presented with weak muscle tone (hypotonia) and problems with the muscles. As they become older, these individuals also develop joint deformities affecting the movements of joints. They may also exhibit muscle stiffness along with the involuntary movements of the limbs. In addition, other symptoms include poor growth, abnormal folding of the ears, developmental delay, poor head control and unclear or no speech. As these people are unable to walk on their own, they are often wheelchair users. Most of these individuals have survived into their 60s, however, the overall life expectancy is compromised.
Causes
This syndrome is inherited in an X-linked recessive pattern meaning the mutated gene is present in one of the two sex hormones. The X-linked disorders only affect the male who carry one X chromosome in comparison to the females who carry two. So, the single copy of the defective gene can cause the disorder, whereas the females will require both the copy of the gene to be defective to develop this condition. As this is more unlikely, males are more affected than the females who are often the carriers of the disorder. The X-linked disorders cannot be passed from the father to the son.
The mutation in the gene SLC16A2 develops allan-herndon-dudley syndrome. This is responsible for delivering the instruction to produce a certain protein essential in the development of the nervous system. This protein delivers a hormone known as triiodothyronine (T3) into the nerve cells. When the gene is defective, the function of the protein is affected causing problems in the transportation of T3 hormone to certain parts of the brain. This affects the normal development of the brain. As the T3 hormones cannot be effectively delivered, its accumulation affects different parts of the body causing symptoms associated with this condition.
Diagnosis
The diagnosis is based on the evaluation of clinical history and examination that shows a neurological and cognitive decline. The laboratory blood analysis can identify elevated levels in free T3 and decreased free T4. The genetic testing can detect the mutation of the gene SLC16A2 (or MCT8) associated with this disorder.
Treatment
There is neither a cure nor an effective treatment available for allan-herndon-dudley syndrome. The supportive care mainly focuses on the reduction and the control of symptoms associated with this condition.
References
https://secure.ssa.gov/poms.nsf/lnx/0423022925
https://ghr.nlm.nih.gov/condition/allan-herndon-dudley-syndrome#diagnosis
http://id.who.int/icd/entity/56813604
