Occurrence of Rett syndrome in boys.

The neurologic disorder Rett syndrome was originally described exclusively in girls. We present two boys with clinical features of Rett syndrome. Other than head circumference deceleration, no longer considered mandatory, patient 1 meets all of the criteria. Using fluorescent in situ hybridization analysis, 97.6% of cells were found to be karyotypically normal (46,XY). No mutation was detected on screening of the coding region of the MECP2 gene. The second patient also has classic features of Rett syndrome. However, cytogenetic analysis of peripheral blood revealed a karyotype 47,XXY[23]/46,XY[7] confirming mosaicism for Klinefelter's syndrome. A T158M missense mutation in the methylcytosine-binding domain of the MECP2 gene was identified. A diagnostic bias against the clinical identification of Rett syndrome in boys may exist. This presentation of the male phenotype could be more common than it would appear, although boys with MECP2 mutations might also manifest in other ways. Rett syndrome remains a clinical diagnosis that should not be dismissed in boys, and thorough evaluation including karyotype and mutation testing is warranted.

Rett syndrome: a surprising result of mutation in MECP2.

The identification of mutations in the gene encoding methyl CpG binding protein 2 (MeCP2) in Rett syndrome represents a major advance in the field. The current model predicts that MeCP2 represses transcription by binding methylated CpG residues and mediating chromatin remodeling. A physical interaction between MeCP2, histone deacetylases and the transcriptional co-repressor Sin3A has been demonstrated, as well as an association of MeCP2 with the basal transcription apparatus. It is unclear, however, whether MeCP2-mediated chromatin remodeling is necessary for transcriptional repression in vivo. Eight recurrent missense and nonsense mutations account for >65% of the mutations identified in Rett syndrome probands, and as predicted from the sporadic nature of the disorder, most mutations are de novo. The severity of the phenotype is likely to reflect the pattern of X chromosome inactivation in relevant tissues, although the type and position of the mutation may also play a role. Although much is known about the biochemical function of MeCP2, the phenotype of Rett syndrome suggests that it plays an unexplored but critical role in development and maintenance of the nervous system.

Rett syndrome and beyond: recurrent spontaneous and familial MECP2 mutations at CpG hotspots.

Rett syndrome (RTT) is a neurodevelopmental disorder characterized by loss of acquired skills after a period of normal development in infant girls. The responsible gene, encoding methyl-CpG binding protein 2 (MeCP2), was recently discovered. Here we explore the spectrum of phenotypes resulting from MECP2 mutations. Both nonsense (R168X and R255X) and missense (R106W and R306C) mutations have been found, with multiple recurrences. R168X mutations were identified in six unrelated sporadic cases, as well as in two affected sisters and their normal mother. The missense mutations were de novo and affect conserved domains of MeCP2. All of the nucleotide substitutions involve C-->T transitions at CpG hotspots. A single nucleotide deletion, at codon 137, that creates a L138X stop codon within the methyl-binding domain was found in an individual with features of RTT and incontinentia pigmenti. An 806delG deletion causing a V288X stop in the transcription-repression domain was identified in a woman with motor-coordination problems, mild learning disability, and skewed X inactivation; in her sister and daughter, who were affected with classic RTT; and in her hemizygous son, who died from congenital encephalopathy. Thus, some males with RTT-causing MECP2 mutations may survive to birth, and female heterozygotes with favorably skewed X-inactivation patterns may have little or no involvement. Therefore, MECP2 mutations are not limited to RTT and may be implicated in a much broader phenotypic spectrum.