Long-read sequence analysis of the MECP2 gene in Rett syndrome patients: correlation of disease severity with mutation type and location

Mutations in the methyl-CpG-binding protein gene MECP2 at Xq28 cause Rett s yndrome (RTT), an X-linked dominant neurodevelopmental disorder characteriz ed by a period of stagnation followed by regression in the development of y oung girls, Mutations were sought in MECP2 in 48 females with classical spo radic RTT, seven families with possible familial RTT and five sporadic fema les with features suggestive, but not diagnostic of RTT, Long distance PCR coupled with long-read direct sequencing was employed to sequence the entir e MECP2 gene coding region in all cases, Mutations were identified in 44/55 (80%) unrelated classical sporadic and familial RTT patients, but only 1/5 (20%) sporadic cases with suggestive but non-diagnostic features of RTT, T wenty-one different mutations were identified (12 missense, four nonsense a nd five frame-shift mutations); 14 of these were novel. All missense mutati ons were located either in the methyl-CpG-binding domain or in the transcri ption repression domain, Nine recurrent mutations were characterized in a t otal of 33 unrelated cases (73% of all cases with MECP2 mutations). Signifi cantly milder disease was noted in patients carrying missense mutations as compared with those with truncating mutations (P = 0.0023), and milder dise ase was associated with late as compared with early truncating mutations (P = 0.0190).