Spectrum of MECP2 mutations in Rett syndrome.

Mutations in the MECP2 (Methyl-CpG-binding protein) gene recently have been reported to cause Rett syndrome (RTT), an X-linked progressive encephalopathy. We have collected the results of MECP2 analysis conducted in four laboratories in France. A total of 301 RTT alleles have been analyzed, demonstrating a total of 69 different mutations so far observed and accounting for 64% of MECP2 genes in RTT patients living in France. R168X (11.5%) is the most common of MECP2 mutations, followed by R255X (10.9%), R270X (10.5%), T158M (7.8%), and R306C (6.8%). Only 10 mutations had a relative frequency > 2%. A total of 59 mutations were found in a small number of RTT alleles (from 1 to 2). These data demonstrate the high allelic heterogeneity of RTT in France and provide information relevant to the development of strategies for molecular diagnosis and genetic counseling in RTT families.