Finding new etiologies of mental retardation and hypotonia: X marks the spot

Dev Med Child Neurol. 2008 Feb;50(2):104-11. doi: 10.1111/j.1469-8749.2007.02022.x. Epub 2008 Jan 7.


Mental retardation (MR) and hypotonia occur together frequently and have a heterogeneous etiology. Molecular and clinical studies have led to the recent discovery of genes on the X chromosome that may be associated with syndromal forms of X-linked MR (XLMR). These disorders manifest additional neurological and somatic features that are helpful in establishing a specific diagnosis and etiology. This article provides an overview of MR and its association with hypotonia, with a review of five 'new' XLMR-hypotonia syndromes.

Publication types

  • Review

MeSH terms

  • Child
  • Chromosomes, Human, X*
  • Humans
  • Membrane Transport Proteins / deficiency
  • Mental Retardation, X-Linked / genetics*
  • Methyl-CpG-Binding Protein 2 / genetics
  • Monocarboxylic Acid Transporters / genetics
  • Muscle Hypotonia / genetics*
  • Muscle Spasticity / genetics
  • Mutation
  • Nerve Tissue Proteins / genetics
  • Plasma Membrane Neurotransmitter Transport Proteins / genetics
  • Sex Chromosome Disorders / diagnosis*
  • Sex Chromosome Disorders / genetics
  • Spermine Synthase / deficiency
  • Symporters
  • alpha-Thalassemia / diagnosis


  • MECP2 protein, human
  • Membrane Transport Proteins
  • Methyl-CpG-Binding Protein 2
  • Monocarboxylic Acid Transporters
  • Nerve Tissue Proteins
  • Plasma Membrane Neurotransmitter Transport Proteins
  • SLC16A2 protein, human
  • SLC6A8 protein, human
  • Symporters
  • creatine transporter
  • Spermine Synthase