Rett syndrome.

The Rett syndrome (RS) was first described in 1966 by Andreas Rett,' 2 who published the first English language account of the condition in 1977 as "Cerebral atrophy with hyperammonaemia".3 Rett syndrome became better known in English language publications when Hagberg et alt described 35 affected girls in 1983. The incidence or prevalence among females has been estimated as 1 in 10-15 000 (incidence) in Scotland,5 1 in 15 000 (preva- lence) in Sweden,6 1 in 20 000 (prevalence) in Dakota, USA,7 and 1 in 22 800 (prevalence) in Texas, USA.8 RS therefore accounts for 2-3% of severe mental handicap9 10 and perhaps 10% of profound handicap in females. Despite its importance, however, the pathogenesis of RS remains obscure. It is most likely to be an X linked dominant disorder, lethal in hemizygous males, but this is not certain and has been con- tested.