title: Allan-Herndon-Dudley syndrome and the monocarboxylate transporter 8 (MCT8) gene.
abstract: Allan-Herndon-Dudley syndrome was among the first of the X-linked mental retardation syndromes to be described (in 1944) and among the first to be regionally mapped on the X chromosome (in 1990). Six large families with the syndrome have been identified, and linkage studies have placed the gene locus in Xq13.2. Mutations in the monocarboxylate transporter 8 gene (MCT8) have been found in each of the six families. One essential function of the protein encoded by this gene appears to be the transport of triiodothyronine into neurons. Abnormal transporter function is reflected in elevated free triiodothyronine and lowered free thyroxine levels in the blood. Infancy and childhood in the Allan-Herndon-Dudley syndrome are marked by hypotonia, weakness, reduced muscle mass, and delay of developmental milestones. Facial manifestations are not distinctive, but the face tends to be elongated with bifrontal narrowing, and the ears are often simply formed or cupped. Some patients have myopathic facies. Generalized weakness is manifested by excessive drooling, forward positioning of the head and neck, failure to ambulate independently, or ataxia in those who do ambulate. Speech is dysarthric or absent altogether. Hypotonia gives way in adult life to spasticity. The hands exhibit dystonic and athetoid posturing and fisting. Cognitive development is severely impaired. No major malformations occur, intrauterine growth is not impaired, and head circumference and genital development are usually normal. Behavior tends to be passive, with little evidence of aggressive or disruptive behavior. Although clinical signs of thyroid dysfunction are usually absent in affected males, the disturbances in blood levels of thyroid hormones suggest the possibility of systematic detection through screening of high-risk populations.
authors.affiliation: JC Self Research Institute of Human Genetics, Greenwood Genetic Center, Greenwood, SC 29646, USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Schwartz
authors.forename: Melanie M
authors.initials: MM
authors.lastname: May
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Carpenter
authors.forename: R Curtis
authors.initials: RC
authors.lastname: Rogers
authors.forename: Judith
authors.initials: J
authors.lastname: Martin
authors.forename: Martin G
authors.initials: MG
authors.lastname: Bialer
authors.forename: Jewell
authors.initials: J
authors.lastname: Ward
authors.forename: Javier
authors.initials: J
authors.lastname: Sanabria
authors.forename: Silvana
authors.initials: S
authors.lastname: Marsa
authors.forename: James A
authors.initials: JA
authors.lastname: Lewis
authors.forename: Roberto
authors.initials: R
authors.lastname: Echeverri
authors.forename: Herbert A
authors.initials: HA
authors.lastname: Lubs
authors.forename: Kytja
authors.initials: K
authors.lastname: Voeller
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Simensen
authors.forename: Roger E
authors.initials: RE
authors.lastname: Stevenson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D041321:Chromosomes, Human, X; D002658:Developmental Disabilities / Q000235:genetics*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D038901:X-Linked Intellectual Disability / Q000235:genetics*; D008875:Middle Aged; D027501:Monocarboxylic Acid Transporters / Q000235:genetics*; D018908:Muscle Weakness / Q000235:genetics; D009154:Mutation; D010264:Paraplegia / Q000235:genetics; D010375:Pedigree; D027981:Symporters
chemical_list: D027501:Monocarboxylic Acid Transporters; C090735:SLC16A2 protein, human; D027981:Symporters