The association of early truncating mutations with nonrandom XCI, along with the fact that chimeric mice lacking methyl-CpG-binding protein 2 (MeCP2) function die during embryogenesis, supports the notion that RTT is caused by partial loss of MeCP2 function.
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.
Mutations were sought in MECP2 in 48 females with classical sporadic RTT, seven families with possible familial RTT and five sporadic females with features suggestive, but not diagnostic of RTT.
The novel disease alleles and benign variants of the MECP2 gene found in this study should contribute to the establishment of a reliable diagnosis of Rett syndrome.
Three of these mutations (R106W, R133C, and F155S) have their binding affinities for methylated DNA reduced more than 100-fold; this is consistent with the hypothesis that impaired selectivity for methylated DNA of mutant MeCP2 contributes to Rett syndrome.
MECP2 encodes a methyl-CpG-binding protein (MeCP2), which is critical for transcriptional silencing of an as yet unknown number and type of genes responsible for the pathobiology of RS.
Together, these results provide evidence of how Rett syndrome mutations can affect distinct functions of MeCP2 and give insight into these mutations that may contribute to the disease.
Collectively, we tested 228 unrelated female patients with a diagnosis of possible (209) or classic (19) RTT and found MECP2 mutations in 83 (40%) of 209 and 16 (84%) of 19 of the patients, respectively.
With the recent identification of MECP2 mutations in Rett syndrome it is quite likely that genetic factors not only play a major role in brain development but may also influence other organ growth including bone formation.
We searched for mutations by sequencing the MECP2 coding region in 45 sporadic cases (35 with classic RTT, eight with variant forms and two males) and in seven families with two or more affected females.
The authors also report the identification of MeCP2 mutations in two males; a Klinefelter's male with classic RTT (T158M) and a hemizygous male infant with a Xq27-28 inversion and a novel 32 bp frameshift deletion [1154(del32)].
Among 60 patients 57 girls with a clinical picture of RTT had normal female karyotype (46,XX), one boy had normal male karyotype in peripheral lymphocytes (46,XY) and two boys had a mosaic form of Kleinfelter's syndrome (47,XXY/46,XY) in peripheral lymphocytes or muscle cells (with MeCP2 mutation R270X).