title: Hypotonic male infant and MCT8 deficiency - a diagnosis to think about.
abstract: BACKGROUND
  Thyroid hormone is crucial in the development of different organs, particularly the brain. MCT8 is a specific transporter of triiodothyronine (T3) hormone and MCT8 gene mutations cause a rare X-linked disorder named MCT8 deficiency, also known as Allan-Herndon-Dudley syndrome, characterized by psychomotor retardation and hypotonia. Typically, elevation of T3 and delayed myelination in cerebral magnetic resonance imaging are found.
  
  
  METHODS
  We present a 24-month-old boy, born from non-consanguineous healthy parents, with severe motor and cognitive delay and global hypotonia, being unable to hold head upright or sit without support. Deep tendon reflexes were absent bilaterally at the ankles. T3 was elevated and thyroxine slightly decreased, consistent with MCT8 deficiency. Genetic studies confirmed the diagnosis.
  
  
  CONCLUSIONS
  Although a rare disease (MCT8 mutations have been reported in about 50 families all around the world), we illustrate the importance of excluding Allan-Herndon-Dudley syndrome in the evaluation of floppy male infants with development delay, without history of perinatal asphyxia. The simple evaluation of thyroid status, including T3, T4 and TSH can guide the diagnosis, avoiding a number of useless, expensive and invasive investigations and allowing appropriate genetic counseling to the affected families.
authors.affiliation: Neuromuscular Unit, Neurology Department, Fundación Sant Joan de Déu, Hospital Materno-Infantil Sant Joan de Déu, Passeig Sant Joan de Déu, 2, 08950 Esplugues de Llobregat, Barcelona, Spain. filipa.a.rodrigues@gmail.com.
authors.forename: Filipa
authors.initials: F
authors.lastname: Rodrigues
authors.forename: Joana
authors.initials: J
authors.lastname: Grenha
authors.forename: Carlos
authors.initials: C
authors.lastname: Ortez
authors.forename: Andrés
authors.initials: A
authors.lastname: Nascimento
authors.forename: Beatriz
authors.initials: B
authors.lastname: Morte
authors.forename: Monica
authors.initials: M
authors.lastname: M-Belinchón
authors.forename: Judith
authors.initials: J
authors.lastname: Armstrong
authors.forename: Jaume
authors.initials: J
authors.lastname: Colomer
mesh_terms: D002675:Child, Preschool; D006801:Humans; D008297:Male; D038901:X-Linked Intellectual Disability / Q000175:diagnosis* / Q000235:genetics; D027501:Monocarboxylic Acid Transporters / Q000235:genetics*; D009123:Muscle Hypotonia / Q000175:diagnosis* / Q000235:genetics; D009133:Muscular Atrophy / Q000175:diagnosis* / Q000235:genetics; D009154:Mutation; D035583:Rare Diseases; D027981:Symporters; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D027501:Monocarboxylic Acid Transporters; C090735:SLC16A2 protein, human; D027981:Symporters; D014284:Triiodothyronine; D013974:Thyroxine