OBJECTIVETo analyze the genetic characteristics and molecular mechanism of Chinese patients with Rett syndrome (RTT) and assess the recurrent risk in order to provide genetic counseling for the family with RTT patient.

METHODSMethyl-CpG-binding protein 2 (MECP2) gene mutation analysis were performed on 405 Chinese RTT cases and 292 mothers of the patients with MECP2 mutations with polymerase chain reaction (PCR), direct sequencing and multiplex ligation-dependent probe amplification (MLPA). Then cyclin-dependent kinase-like 5 (CDKL5) and forkhead box protein G1 (FOXG1) genes mutation analysis were performed on the patients without MECP2 mutation. Parental origin of mutated MECP2 gene was detected with allele specific PCR analysis. Based on the difference methylation in CpG island of the first exon of human androgen-receptor gene on active and inactive X-chromosomes, methylation sensitive restriction endonuclease digestion was used to analyze the X-chromosome inactive (XCI) patterns.

RESULTSMECP2 gene mutation was found in 86.9% RTT cases. CDKL5 gene mutation was found in only 3 cases with early-onset seizures variant. No FOXG1 mutation was found. There were 94.4% MECP2 mutations of paternal origin,and point mutations were common. However, microdeletions were common in maternal origin mutation. MECP2 gene mutation was found in only 1 (0.34%,1/292) mother with normal phenotype and non-random XCI pattern. Her daughter was a RTT patient with preserved speech variant, and her XCI pattern was random.

CONCLUSIONMECP2 is the main pathogenic gene in RTT. CDKL5 gene should be screened in patients with early-onset seizures variant without MECP2 gene mutation. The majority of RTT patients had paternally derived de novo MECP2 gene mutation, which may explain the high female to male ratio in RTT. Only 0.34% mothers carried the pathogenic mutation, indicating a lower recurrent risk for RTT families. The XCI may modulate the phenotype of RTT, so MECP2 gene mutation screening in the mothers is important for genetic counseling.