In a collaborative Swedish-Norwegian project, at Goteborg Sweden and Oslo, Norway, a model for the clinical delineation of atypical cases of Rett syndrome was applied to a pilot series of 16 mentally retarded females, aged 11 to 47 years (median: 23). The atypical variants included forme fruste cases (8), late regression (6), and congenital variants (2). The model was based on age >10 years, 3 of 6 primary inclusion criteria for RS (eg. hand stereotypies, decelerated head growth, stages of regression and recovery of contact), and 5 of 11 supportive characteristics (eg. breathing irregularities, air swallowing, teeth grinding, gait dyspraxia, scoliosis). The model identified RS variants and distinguished them from other disorders, eg. Angelman’s syndrome that fulfilled 3 supportive criteria. 
COMMENT. For a review of recent international research on RS, see “Rett syndrome: from gene to gesture.” J R Soc Med Sept 1994;87:562-566).