"Forme fruste" of Rett syndrome--a case report.

We report on a 17-year-old girl considered to represent a "forme fruste" of Rett syndrome. The history showed normal psychomotor development until age 20 months, when the girl successively lost acquired speech and developed autistic traits, moderate dementia, partial apraxia and microcephaly. However, she never stopped using her hands purposefully, nor did she develop the hand stereotypies characteristic of Rett syndrome. From age 4 years she successively became more communicable and regained some of the previous abilities including some speech. At 17 she showed most of the abnormalities characteristic of adolescent girls with Rett syndrome but was still only moderately retarded, with remarkably preserved motor functions. She had a peculiar apraxia. She seemed to lack "the key" to using her hands, while retaining a pincer grasp and some manipulative skills in her fingers. - It is suggested that the phenotype of Rett syndrome can vary considerably and that "formes frustes" may not be an exceptional rarity among mentally retarded girls.