Duplications of the X-linked MECP2 gene are associated with moderate to severe intellectual disability, epilepsy, and neuropsychiatric illness in males, while triplications are associated with a more severe phenotype.
The two males and the two obligate carrier females presented a mutation in the MECP2 gene, demonstrating that, in males, MECP2 can be responsible for severe mental retardation associated with neurological disorders.
Rett syndrome (RTT) is a pervasive neurodevelopmental disorder mainly caused by mutations in the X-linked MECP2 gene associated with severe intellectual disability, movement disorders, and autistic-like behaviors.
Rett syndrome is an X-linked dominant neurodevelopmental disorder manifesting with severe intellectual disability in females caused by various mutations in the MECP2 gene.
Duplications encompassing the MECP2 gene on the Xq28 region have been described in male patients with moderate to severe mental retardation, absent speech, neonatal hypotonia, progressive spasticity and/or ataxia, recurrent severe respiratory infections, gastrointestinal problems, mild facial dysmorphisms (midface hypoplasia, depressed nasal bridge, large ears) and epilepsy.
MECP2 mutations have subsequently been identified in patients with a variety of clinical syndromes ranging from mild learning disability in females to severe mental retardation, seizures, ataxia, and sometimes neonatal encephalopathy in males.
However, the recent identification of mutations in the MECP2 gene in affected males indicates that screening of the MECP2 gene should be considered also in males with severe mental retardation (MR) in whom the most common forms of MR have been excluded.
Xq28 duplications including MECP2 are a well-known cause of severe mental retardation in males with seizures, muscular hypotonia, progressive spasticity, poor speech and recurrent infections that often lead to early death.
We propose to implement DNA copy number testing for MECP2 in the current diagnostic testing in all males with moderate to severe mental retardation accompanied by (progressive) neurological symptoms.
We speculate that the translocation may disrupt the proper regulation of MEF2C expression in the developing brain, resulting in severe intellectual disability and early-onset epileptic encephalopathy.
Although validation in additional patients is required, our findings suggest that the dysmorphic features and severe intellectual disability characteristic of PTHS are partially rescued by overexpression of those short TCF4 transcripts encoding a nuclear localization signal, a transcription activation domain, and the basic helix-loop-helix domain.
We therefore performed mutational analysis in 362 patients with severe mental retardation and found two truncating and two missense de novo mutations in MEF2C, establishing defects in this transcription factor as a novel relatively frequent autosomal dominant cause of severe mental retardation accounting for as much as 1.1% of patients.
TCF4 (transcription factor 4; E2-2, ITF2) is a transcription factor that when haplo-insufficient causes Pitt-Hopkins Syndrome (PTHS), an autism-spectrum disorder that is associated with pervasive developmental delay and severe intellectual disability.
Sequencing of the TCF4 transcription factor gene, which is contained in the deletion region, in 30 patients with significant phenotypic overlap revealed heterozygous stop, splice, and missense mutations in five further patients with severe mental retardation and remarkable facial resemblance.
5q14.3 deletions spanning and flanking MEF2C as well as intragenic MEF2C mutations have recently been described as a cause of severe intellectual disability, epilepsy, and muscular hypotonia, with variable brain and other anomalies.
The purpose of this work was to clarify criteria for the selection of patients with severe intellectual disability to screen for deficiency in the MEF2C gene.
Severe intellectual disability with inability to speak and epilepsy are universal features in patients with MEF2C mutations, although mild cognitive and speech disorders have been reported to occur in patients with duplications.