Survey of adolescents with severe intellectual

A diagnostic survey was undertaken ofchildren aged 11 to 19 years in Tameside with severe learning difficulties (intelligence quotient s<50). Eighty two children were identified and their medical records reviewed. A specific diagnosis for the retardation was documented in 25 (30%) of the children, 18 of whom had Down's syndrome. A probable aetiology or a disorder of unknown aetiology had been identified in a further 21 (26%) children. To confirm the existing diagnosis, identify new diagnoses, and offer genetic counselling, the parents of 63 children were offered detailed reassessment of their child. Fifty three children were reviewed, and a specific disorder identified in 25 out of 31 previously undiagnosed children. The most frequent diagnoses made were fragile X syndrome and Rett's syndrome. On completion of the survey, 61 of the 82 children (74%) had a specific diagnosis or probable aetiology identified, 12 (15%) had associated disorders such as cerebral palsy, and in only nine of the 82 children (11%) were there no clues at all to the cause of their retardation. fragile X chromosome was first demonstrated by Lubs in 1969,8 and its folic acid dependent expression and association with mental retardation reported in 1977.9 "0 The definition of the clinical syndrome during the late 1970s and early 1980s is summarised by Fryns."1 This disorder is now thought to be the second most common cause of mental retardation after Down's syndrome, with an estimated prevalence of 0 3-1/1000 males and 0-2-0-6/ 1000 females. 12-14 Identification of this inherited disorder in retarded children is important because of the genetic implications. Many aspects of the condition are not understood, however,'5 including transmission by apparently unaffected males, and the high proportion of heterozygous females who have some intellectual impairment usually of mild to moderate degree. The present study initiated by one of the authors (JCA) was undertaken to identify severely retarded children with fragile X syndrome in the Tameside borough, and where possible to reach a diagnosis in other children with previously unexplained severe retardation, so that families could be offered genetic counselling. Community Child Health, Tameside and Glossop Health Authority