Disease Information for Allan-Herndon Mental Retardation/X-linked

Clinical Manifestations
Signs & Symptoms
Hyperextensable Joints Infant
Bitemporal narrowing/Bifrontal narrowing
Congenital facial deformities
Craniofacial Abnormalities/Congenital
Long thin face
Tongue Protrudes Infant
Delay Sitting Unsupported Infant
Flexion contractures/extremities
Head Lag Infant Sign
Mouth Hangs Open Infant
Muscle Atrophy
Muscle spasticity
Muscle weakness
Muscles Soft/Doughy Infant
Neck weakness/head nodding
Rolling Over Delay Infant
Weakness, legs, bilateral
Babinski's upgoing toes/bilateral
Babkin infant sign/Abnormal
Chorea signs
Choreoathetoid movement
Delayed speech/language development
Delayed walking milestone/child
Development Motor Skills (Milestones) Delayed
Galant Infant reflex/Abnormal
Head Neck Floppy Infant Hypotonia Sign
Hyperreflexia/DTRs increased
Infant Head Support Delay
Mental Deficiency Child
Moro reflex Poor/Absent Infant
Palmar Grasp infant Reflex Abnormal
Poor head control/infant
Primitive infant reflexes/Abnormal
Psychomotor regression/infant/child
Regressing neuromotor/skills child/signs
Rooting infant sign/Abnormal
Staggering Gait
Swimming infant reflex/Abnormal
Tonic Neck Infant reflex/Abnormal
Unable to walk
Shallow Breathing Infant
Good Bonding Social Skills
Psychomotor retardation
Sternum deformities
Delayed speech development/impediment
Difficulty Talking
Muscle Wasting/Diffuse
Big ears
Prominent Ears
Disease Progression
Onset/Six months
Demographics & Risk Factors
Population Group
Population/Pediatrics population
Sex & Age Groups
Population/Infant male
Laboratory Tests
Abnormal Lab Findings - Increased
T3 (RIA) serum level (Lab)
Tri-iodothyronine/T3 as Resin Uptake (Lab)
Associated Diseases & Rule outs
Associated Disease & Complications
Allan-Herndon Mental Retardation syndrome
Congenital anomalies
Facial dysplasia
Joint contractures
Mental retardation
Multiple Congenital Anomalies
Multiple congenital anomalies/Mental retardation
Neonatal Hypotonia/Floppy Baby Syndrome
Paraplegia, spastic
Pectus excavatum
Ataxia Disorder
Disease Mechanism & Classification
CLASS/Jablonski/NIH Archive Anomalies Database
CLASS/Pediatric disorders (ex)
Pathophysiology/Gene locus Chromosome X.
Pathophysiology/Gene locus Chromosome Xq
Pathophysiology/Gene locus Xq11.4-q21.3
Pathophysiology/SLC16A2 (MCT8) Gene Mutation
Pathophysiology/T3 unable to enter nerve cells
Pathophysiology/Maternal Chromosome mutation
PROCESS/Eponymic (category)
PROCESS/Genetic disorder/Spontaneous mutations/sporadic
PROCESS/Hereditofamilial (category)
PROCESS/INCIDENCE/Extremely rare disease
PROCESS/INCIDENCE/Rare disease (ex)
PROCESS/Sex-linked (X-linked) recessive inheritance (ex)
PROCESS/Dystostosis/craniofacial (ex)
Mental Retardation X Linked, Retardation X Linked Mental, X Linked Mental Retardation, X LINKED MENTAL RETARDATION DIS, X Linked Mental Retardation Disorders, X Linked Mental Retardation Syndromes, X Linked Mental Retardations, Synonm/Allan-Herndon-Dudley syndrome (AHDS), Synonym/X-linked mental retardation, Synonym/X-linked mental retardation with Hypotonia

Synonyms of Allan Herndon Syndrome; AHDS;

Allan-Herndon-Dudley Mental Retardation; Allan-Herndon-Dudley Syndrome; X-Linked Mental Retardation with Hypotonia

Discussion : Allan-Herndon syndrome is an extremely rare inherited disorder that may be characterized by severe mental retardation, an impaired ability to form words and speak clearly (dysarthria), diminished muscle tone (hypotonia), and/or movement abnormalities; With the exception of poor muscle tone, most affected infants appear to develop normally during the first months of life; However, by about six months of age, affected infants may seem weak and have an inability to hold up the head; Due to hypotonia, severely reduced motor development, and other abnormalities, affected children may not develop the ability to walk or may walk with difficulty; Associated features often include underdevelopment (hypoplasia) and wasting (atrophy) of muscle tissue; weakness and stiffness of the legs (spastic paraplegia) with exaggerated reflexes (hyperreflexia); relatively slow, involuntary, purposeless, writhing movements (athetoid movements); and/or other movement abnormalities; Affected individuals may also have abnormalities of the skull and facial (craniofacial)

region; Allan-Herndon syndrome is thought to be inherited as an X-linked recessive trait and therefore is typically fully expressed in males only----[NORD 2005]----------

Allan-Herndon-Dudley syndrome is a rare disorder of brain development that causes moderate to severe mental retardation and problems with movement; This condition, which occurs exclusively in males, disrupts development from before birth; Although affected males have impaired speech and a limited ability to communicate, they seem to enjoy interaction with other people; Most children with Allan-Herndon-Dudley syndrome have weak muscle tone (hypotonia) and underdevelopment of many muscles (muscle hypoplasia); As they get older, they usually develop joint deformities called contractures, which restrict the movement of certain joints; Abnormal muscle stiffness (spasticity), muscle weakness, and involuntary movements of the arms and legs also limit mobility; As a result, many people with Allan-Herndon-Dudley syndrome are unable to walk independently and become wheelchair-bound by adulthood; Allan-Herndon-Dudley syndrome appears to be a rare disorder; About 25 families with individuals affected by this condition have been reported worldwide; Mutations in the SLC16A2 gene cause Allan-Herndon-Dudley syndrome; The SLC16A2 gene, also known as MCT8, provides instructions for making a protein that plays a critical role in the development of the nervous system; This protein transports a particular hormone into nerve cells in the developing brain; This hormone, called triiodothyronine or T3, is produced by a butterfly-shaped gland in the lower neck called the thyroid; T3 appears to be critical for the normal formation and growth of nerve cells, as well as the development of junctions between nerve cells (synapses) where cell-to-cell communication occurs; T3 and other forms of thyroid hormone also help regulate the development of other organs and control the rate of chemical reactions in the body (metabolism); Gene mutations alter the structure and function of the SLC16A2 protein; As a result, this protein is unable to transport T3 into nerve cells effectively; A lack of this critical hormone in certain parts of the brain disrupts normal brain development, resulting in mental retardation and problems with movement; Because T3 is not taken up by nerve cells, excess amounts of this hormone continue to circulate in the bloodstream; Increased T3 levels in the blood may be toxic to some organs and contribute to the signs and symptoms of Allan-Herndon-Dudley syndrome; This condition is inherited in an X-linked recessive pattern; A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes; In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition


External Links Related to Allan-Herndon Mental Retardation/X-linked
PubMed (National Library of Medicine)
NGC (National Guideline Clearinghouse)
Medscape (eMedicine)
Harrison's Online (accessmedicine)
NEJM (The New England Journal of Medicine)