[MECP2 gene mutations in twenty-six cases with atypical Rett syndrome]

Rett syndrome (RTT) is an X-linked progressive neurodeveopmental disorder that almost exclusively affects girls, and is one of the most common causes of mental retardation in females, with an estimated prevalence of approximately 1 in 10,000 - 15,000 female individuals. Mutations in X-linked methyl-CpG-binding protein 2 (MECP2) gene, located on chromosome Xq28, have been found to be a cause of RS. A lot of mutations have been reported to be related to RS recently. Mutations are found in 70% - 85% of patients with classical RTT and in less than 50% of patients with atypical RS. Up to now, RTT is diagnosed based on a consistent counseling for clinical features and the established diagnostic criteria. The present study aimed to investigate frequency and type of mutation of MECP2 gene and if hot spot of mutation exits in patients with atypical RTT and find out the relationship between genotype and phenotype.

A systematic analysis of the entire coding region of MECP2 in 26 unrelated patients with atypical RTT was performed by polymerase chain reaction (PCR) and direct sequencing. Genomic DNA was extracted using standard procedures from the peripheral blood leukocytes of each patient. PCR amplification products were checked by 2% agarose gel electrophoresis and were subsequently sequenced with ABI 3730 Automated DNA Sequencer with both the forward and reverse primers. Mutational analyses were performed using normal human genomic MECP2 sequence as a reference (GenBank accession NO.AF030876).

Seven mutations were identified in 12 of 26 patients. Most of the mutations were missense mutation; c.397C > T (R133C) was found in 3 of 26 patients; c.473C > T (T158M) and c.916C > T (R306C) were found in 2 of 26 patients, respectively; c.397A > G (R133H) and c.1005G > A (R335C) were found in 1 of 26 patients, respectively. One base pair deletion mutation (806delG) resulting in frameshift was found in 2 of 26 patients, and 1 base pair transversion at splice accept-site (IVS3-2A > T).

The results of this study indicated that c.397C > T (R133C), c.473C > T (T158M) and c.916C > T (R306C) were hot spot mutations in MECP2 gene of patients with atypical RTT. There was some relationship between genotype and phenotype.